What are the 100 most cited fungal genera?

The global diversity of fungi has been estimated between 2 to 11 million species, of which only about 155 000 have been named. Most fungi are invisible to the unaided eye, but they represent a major component of biodiversity on our planet, and play essential ecological roles, supporting life as we know it. Although approximately 20 000 fungal genera are presently recognised, the ecology of most remains undetermined. Despite all this diversity, the mycological community actively researches some fungal genera more commonly than others. This poses an interesting question: why have some fungal genera impacted mycology and related fields more than others? To address this issue, we conducted a bibliometric analysis to identify the top 100 most cited fungal genera. A thorough database search of the Web of Science, Google Scholar, and PubMed was performed to establish which genera are most cited. The most cited 10 genera are Saccharomyces, Candida, Aspergillus, Fusarium, Penicillium, Trichoderma, Botrytis, Pichia, Cryptococcus and Alternaria. Case studies are presented for the 100 most cited genera with general background, notes on their ecology and economic significance and important research advances. This paper provides a historic overview of scientific research of these genera and the prospect for further research. Citation: Bhunjun CS, Chen YJ, Phukhamsakda C, Boekhout T, Groenewald JZ, McKenzie EHC, Francisco EC, Frisvad JC, Groenewald M, Hurdeal VG, Luangsa-ard J, Perrone G, Visagie CM, Bai FY, Blaszkowski J, Braun U, de Souza FA, de Queiroz MB, Dutta AK, Gonkhom D, Goto BT, Guarnaccia V, Hagen F, Houbraken J, Lachance MA, Li JJ, Luo KY, Magurno F, Mongkolsamrit S, Robert V, Roy N, Tibpromma S, Wanasinghe DN, Wang DQ, Wei DP, Zhao CL, Aiphuk W, Ajayi-Oyetunde O, Arantes TD, Araujo JC, Begerow D, Bakhshi M, Barbosa RN, Behrens FH, Bensch K, Bezerra JDP, Bilanski P, Bradley CA, Bubner B, Burgess TI, Buyck B, Cadez N, Cai L, Calaça FJS, Campbell LJ, Chaverri P, Chen YY, Chethana KWT, Coetzee B, Costa MM, Chen Q, Custódio FA, Dai YC, Damm U, de Azevedo Santiago ALCM, De Miccolis Angelini RM, Dijksterhuis J, Dissanayake AJ, Doilom M, Dong W, Alvarez-Duarte E, Fischer M, Gajanayake AJ, Gené J, Gomdola D, Gomes AAM, Hausner G, He MQ, Hou L, Iturrieta-González I, Jami F, Jankowiak R, Jayawardena RS, Kandemir H, Kiss L, Kobmoo N, Kowalski T, Landi L, Lin CG, Liu JK, Liu XB, Loizides M, Luangharn T, Maharachchikumbura SSN, Makhathini Mkhwanazi GJ, Manawasinghe IS, Marin-Felix Y, McTaggart AR, Moreau PA, Morozova OV, Mostert L, Osiewacz HD, Pem D, Phookamsak R, Pollastro S, Pordel A, Poyntner C, Phillips AJL, Phonemany M, Promputtha I, Rathnayaka AR, Rodrigues AM, Romanazzi G, Rothmann L, Salgado-Salazar C, Sandoval-Denis M, Saupe SJ, Scholler M, Scott P, Shivas RG, Silar P, Souza-Motta CM, Silva-Filho AGS, Spies CFJ, Stchigel AM, Sterflinger K, Summerbell RC, Svetasheva TY, Takamatsu S, Theelen B, Theodoro RC, Thines M, Thongklang N, Torres R, Turchetti B, van den Brule T, Wang XW, Wartchow F, Welti S, Wijesinghe SN, Wu F, Xu R, Yang ZL, Yilmaz N, Yurkov A, Zhao L, Zhao RL, Zhou N, Hyde KD, Crous PW (2024). What are the 100 most cited fungal genera? Studies in Mycology 108: 1-411. doi: 10.3114/sim.2024.108.01.

Phylogenomic analysis of the Candida auris-Candida haemuli clade and related taxa in the Metschnikowiaceae, and proposal of thirteen new genera, fifty-five new combinations and nine new species.

Candida is a polyphyletic genus of asexually reproducing yeasts in the Saccharomycotina with more than 400 species that occur in almost all families of the subclass and its name is strongly connected with the infectious disease candidiasis. During the last two decades, approximately half of the Candida species have been reassigned into more than 36 already existing genera and 14 newly proposed genera, but the polyphyletic feature of the genus largely remained. Candida auris is an important, globally emerging opportunistic pathogen that has caused life-threatening outbreaks in healthcare facilities worldwide. This species belongs to the Candida auris-Candida haemuli (CAH) clade in the Metschnikowiaceae, a clade that contains multidrug-resistant clinically relevant species, but also species isolated from natural environments. The clade is phylogenetically positioned remotely from the type species of the genus Candida that is Candida vulgaris (currently interpreted as a synonym of Candida tropicalis) and belongs to the family Debaryomycetaceae. Although previous phylogenetic and phylogenomic studies confirmed the position of C. auris in the Metschnikowiaceae, these analyses failed to resolve the position of the CAH clade within the family and its delimitation from the genera Clavispora and Metschnikowia. To resolve the position of the CAH clade, phylogenomic and comparative genomics analyses were carried out to address the phylogenetic position of C. auris and related species in the Metschnikowiaceae using several metrics, such as the average amino acid identity (AAI) values, the percentage of conserved proteins (POCP) and the presence-absence patterns of orthologs (PAPO). Based on those approaches, 13 new genera are proposed for various Candida and Hyphopichia species, including members of the CAH clade in the Metschnikowiaceae. As a result, C. auris and related species are reassigned to the genus Candidozyma. Fifty-five new combinations and nine new species are introduced and this will reduce the polyphyly of the genus Candida. Citation: Liu F, Hu Z-D, Zhao X-M, et al. 2024. Phylogenomic analysis of the Candida auris-Candida haemuli clade and related taxa in the Metschnikowiaceae, and proposal of thirteen new genera, fifty-five new combinations and nine new species. Persoonia 52: 22-43. https://doi.org/10.3767/persoonia.2024.52.02 .

A genome-informed higher rank classification of the biotechnologically important fungal subphylum Saccharomycotina.

The subphylum Saccharomycotina is a lineage in the fungal phylum Ascomycota that exhibits levels of genomic diversity similar to those of plants and animals. The Saccharomycotina consist of more than 1 200 known species currently divided into 16 families, one order, and one class. Species in this subphylum are ecologically and metabolically diverse and include important opportunistic human pathogens, as well as species important in biotechnological applications. Many traits of biotechnological interest are found in closely related species and often restricted to single phylogenetic clades. However, the biotechnological potential of most yeast species remains unexplored. Although the subphylum Saccharomycotina has much higher rates of genome sequence evolution than its sister subphylum, Pezizomycotina, it contains only one class compared to the 16 classes in Pezizomycotina. The third subphylum of Ascomycota, the Taphrinomycotina, consists of six classes and has approximately 10 times fewer species than the Saccharomycotina. These data indicate that the current classification of all these yeasts into a single class and a single order is an underappreciation of their diversity. Our previous genome-scale phylogenetic analyses showed that the Saccharomycotina contains 12 major and robustly supported phylogenetic clades; seven of these are current families (Lipomycetaceae, Trigonopsidaceae, Alloascoideaceae, Pichiaceae, Phaffomycetaceae, Saccharomycodaceae, and Saccharomycetaceae), one comprises two current families (Dipodascaceae and Trichomonascaceae), one represents the genus Sporopachydermia, and three represent lineages that differ in their translation of the CUG codon (CUG-Ala, CUG-Ser1, and CUG-Ser2). Using these analyses in combination with relative evolutionary divergence and genome content analyses, we propose an updated classification for the Saccharomycotina, including seven classes and 12 orders that can be diagnosed by genome content. This updated classification is consistent with the high levels of genomic diversity within this subphylum and is necessary to make the higher rank classification of the Saccharomycotina more comparable to that of other fungi, as well as to communicate efficiently on lineages that are not yet formally named. Taxonomic novelties: New classes: Alloascoideomycetes M. Groenew., Hittinger, Opulente & A. Rokas, Dipodascomycetes M. Groenew., Hittinger, Opulente & A. Rokas, Lipomycetes M. Groenew., Hittinger, Opulente, A. Rokas, Pichiomycetes M. Groenew., Hittinger, Opulente & A. Rokas, Sporopachydermiomycetes M. Groenew., Hittinger, Opulente & A. Rokas, Trigonopsidomycetes M. Groenew., Hittinger, Opulente & A. Rokas. New orders: Alloascoideomycetes: Alloascoideales M. Groenew., Hittinger, Opulente & A. Rokas; Dipodascomycetes: Dipodascales M. Groenew., Hittinger, Opulente & A. Rokas; Lipomycetes: Lipomycetales M. Groenew., Hittinger, Opulente & A. Rokas; Pichiomycetes: Alaninales M. Groenew., Hittinger, Opulente & A. Rokas, Pichiales M. Groenew., Hittinger, Opulente & A. Rokas, Serinales M. Groenew., Hittinger, Opulente & A. Rokas; Saccharomycetes: Phaffomycetales M. Groenew., Hittinger, Opulente & A. Rokas, Saccharomycodales M. Groenew., Hittinger, Opulente & A. Rokas; Sporopachydermiomycetes: Sporopachydermiales M. Groenew., Hittinger, Opulente & A. Rokas; Trigonopsidomycetes: Trigonopsidales M. Groenew., Hittinger, Opulente & A. Rokas. New families: Alaninales: Pachysolenaceae M. Groenew., Hittinger, Opulente & A. Rokas; Pichiales: Pichiaceae M. Groenew., Hittinger, Opulente & A. Rokas; Sporopachydermiales: Sporopachydermiaceae M. Groenew., Hittinger, Opulente & A. Rokas. Citation: Groenewald M, Hittinger CT, Bensch K, Opulente DA, Shen X-X, Li Y, Liu C, LaBella AL, Zhou X, Limtong S, Jindamorakot S, Gonçalves P, Robert V, Wolfe KH, Rosa CA, Boekhout T, Cadez N, Péter G, Sampaio JP, Lachance M-A, Yurkov AM, Daniel H-M, Takashima M, Boundy-Mills K, Libkind D, Aoki K, Sugita T, Rokas A (2023). A genome-informed higher rank classification of the biotechnologically important fungal subphylum Saccharomycotina. Studies in Mycology 105: 1-22. doi: 10.3114/sim.2023.105.01 This study is dedicated to the memory of Cletus P. Kurtzman (1938-2017), a pioneer of yeast taxonomy.

Phytophthora : taxonomic and phylogenetic revision of the genus.

Many members of the Oomycota genus Phytophthora cause economic and environmental impact diseases in nurseries, horticulture, forest, and natural ecosystems and many are of regulatory concern around the world. At present, there are 223 described species, including eight unculturable and three lost species. Twenty-eight species need to be redescribed or validated. A lectotype, epitype or neotype was selected for 20 species, and a redescription based on the morphological/molecular characters and phylogenetic placement is provided. In addition, the names of five species are validated: P. cajani, P. honggalleglyana (Synonym: P. hydropathica), P. megakarya, P. pisi and P. pseudopolonica for which morphology and phylogeny are given. Two species, P. ×multiformis and P. uniformis are presented as new combinations. Phytophthora palmivora is treated with a representative strain as both lecto- and epitypification are pending. This manuscript provides the updated multigene phylogeny and molecular toolbox with seven genes (ITS rDNA, ß-tub, COI, EF1α, HSP90, L10, and YPT1) generated from the type specimens of 212 validly published, and culturable species (including nine hybrid taxa). The genome information of 23 types published to date is also included. Several aspects of the taxonomic revision and phylogenetic re-evaluation of the genus including species concepts, concept and position of the phylogenetic clades recognized within Phytophthora are discussed. Some of the contents of this manuscript, including factsheets for the 212 species, are associated with the "IDphy: molecular and morphological identification of Phytophthora based on the types" online resource (https://idtools.org/tools/1056/index.cfm). The first version of the IDphy online resource released to the public in September 2019 contained 161 species. In conjunction with this publication, we are updating the IDphy online resource to version 2 to include the 51 species recently described. The current status of the 223 described species is provided along with information on type specimens with details of the host (substrate), location, year of collection and publications. Additional information is provided regarding the ex-type culture(s) for the 212 valid culturable species and the diagnostic molecular toolbox with seven genes that includes the two metabarcoding genes (ITS and COI) that are important for Sanger sequencing and also very valuable Molecular Operational Taxonomic Units (MOTU) for second and third generation metabarcoding High-throughput sequencing (HTS) technologies. The IDphy online resource will continue to be updated annually to include new descriptions. This manuscript in conjunction with IDphy represents a monographic study and the most updated revision of the taxonomy and phylogeny of Phytophthora, widely considered one of the most important genera of plant pathogens. Taxonomic novelties: New species: Phytophthora cajani K.S. Amin, Baldev & F.J. Williams ex Abad, Phytophthora honggalleglyana Abad, Phytophthora megakarya Brasier & M.J. Griffin ex Abad, Phytophthora pisi Heyman ex Abad, Phytophthora pseudopolonica W.W. Li, W.X. Huai & W.X. Zhao ex Abad & Kasiborski; New combinations: Phytophthora ×multiformis (Brasier & S.A. Kirk) Abad, Phytophthora uniformis (Brasier & S.A. Kirk) Abad; Epitypifications (basionyms): Peronospora cactorum Lebert & Cohn, Pythiacystis citrophthora R.E. Sm. & E.H. Sm., Phytophthora colocasiae Racib., Phytophthora drechsleri Tucker, Phytophthora erythroseptica Pethybr., Phytophthora fragariae Hickman, Phytophthora hibernalis Carne, Phytophthora ilicis Buddenh. & Roy A. Young, Phytophthora inundata Brasier et al., Phytophthora megasperma Drechsler, Phytophthora mexicana Hotson & Hartge, Phytophthora nicotianae Breda de Haan, Phytophthora phaseoli Thaxt., Phytophthora porri Foister, Phytophthora primulae J.A. Toml., Phytophthora sojae Kaufm. & Gerd., Phytophthora vignae Purss, Pythiomorpha gonapodyides H.E. Petersen; Lectotypifications (basionym): Peronospora cactorum Lebert & Cohn, Pythiacystis citrophthora R.E. Sm. & E.H. Sm., Phytophthora colocasiae Racib., Phytophthora drechsleri Tucker, Phytophthora erythroseptica Pethybr., Phytophthora fragariae Hickman, Phytophthora hibernalis Carne, Phytophthora ilicis Buddenh. & Roy A. Young, Phytophthora megasperma Drechsler, Phytophthora mexicana Hotson & Hartge, Phytophthora nicotianae Breda de Haan, Phytophthora phaseoli Thaxt., Phytophthora porri Foister, Phytophthora primulae J.A. Toml., Phytophthora sojae Kaufm. & Gerd., Phytophthora vignae Purss, Pythiomorpha gonapodyides H.E. Petersen; Neotypifications (basionym): Phloeophthora syringae Kleb., Phytophthora meadii McRae Citation: Abad ZG, Burgess TI, Bourret T, Bensch K, Cacciola S, Scanu B, Mathew R, Kasiborski B, Srivastava S, Kageyama K, Bienapfl JC, Verkleij G, Broders K, Schena L, Redford AJ (2023). Phytophthora: taxonomic and phylogenetic revision of the genus. Studies in Mycology 106: 259-348. doi: 10.3114/sim.2023.106.05.

Taxonomy, phylogeny and identification of Chaetomiaceae with emphasis on thermophilic species.

Chaetomiaceae comprises phenotypically diverse species, which impact biotechnology, the indoor environment and human health. Recent studies showed that most of the traditionally defined genera in Chaetomiaceae are highly polyphyletic. Many of these morphology-based genera, such as Chaetomium, Thielavia and Humicola, have been redefined using multigene phylogenetic analysis combined with morphology; however, a comprehensive taxonomic overview of the family is lacking. In addition, the phylogenetic relationship of thermophilic Chaetomiaceae species with non-thermophilic taxa in the family is largely unclear due to limited taxon sampling in previous studies. In this study, we provide an up-to-date overview on the taxonomy and phylogeny of genera and species belonging to Chaetomiaceae, including an extensive taxon sampling of thermophiles. A multigene phylogenetic analysis based on the ITS (internal transcribed spacers 1 and 2 including the 5.8S nrDNA), LSU (D1/D2 domains of the 28S nrDNA), rpb2 (partial RNA polymerase II second largest subunit gene) and tub2 (ß-tubulin gene) sequences was performed on 345 strains representing Chaetomiaceae and 58 strains of other families in Sordariales. Divergence times based on the multi-gene phylogeny were estimated as aid to determine the genera in the family. Genera were delimited following the criteria that a genus must be a statistically well-supported monophyletic clade in both the multigene phylogeny and molecular dating analysis, fall within a divergence time of over 27 million years ago, and be supported by ecological preference or phenotypic traits. Based on the results of the phylogeny and molecular dating analyses, combined with morphological characters and temperature-growth characteristics, 50 genera and 275 species are accepted in Chaetomiaceae. Among them, six new genera, six new species, 45 new combinations and three new names are proposed. The results demonstrate that the thermophilic species fall into seven genera (Melanocarpus, Mycothermus, Remersonia, Thermocarpiscus gen. nov., Thermochaetoides gen. nov., Thermothelomyces and Thermothielavioides). These genera cluster in six separate lineages, suggesting that thermophiles independently evolved at least six times within the family. A list of accepted genera and species in Chaetomiaceae, together with information on their MycoBank numbers, living ex-type strains and GenBank accession numbers to ITS, LSU, rpb2 and tub2 sequences is provided. Furthermore, we provide suggestions how to describe and identify Chaetomiaceae species. Taxonomic novelties: new genera: Parvomelanocarpus X.Wei Wang & Houbraken, Pseudohumicola X.Wei Wang, P.J. Han, F.Y. Bai & Houbraken, Tengochaeta X.Wei Wang & Houbraken, Thermocarpiscus X.Wei Wang & Houbraken, Thermochaetoides X.Wei Wang & Houbraken, Xanthiomyces X.Wei Wang & Houbraken; New species: Botryotrichum geniculatum X.Wei Wang, P.J. Han & F.Y. Bai, Chaetomium subaffine Sergejeva ex X.Wei Wang & Houbraken, Humicola hirsuta X.Wei Wang, P.J. Han & F.Y. Bai, Subramaniula latifusispora X.Wei Wang, P.J. Han & F.Y. Bai, Tengochaeta nigropilosa X.Wei Wang & Houbraken, Trichocladium tomentosum X.Wei Wang, P.J. Han & F.Y. Bai; New combinations: Achaetomiella gracilis (Udagawa) Houbraken, X.Wei Wang, P.J. Han & F.Y. Bai, Allocanariomyces americanus (Cañete-Gibas et al.) Cañete-Gibas, Wiederhold, X.Wei Wang & Houbraken, Amesia dreyfussii (Arx) X.Wei Wang & Houbraken, Amesia raii (G. Malhotra & Mukerji) X.Wei Wang & Houbraken, Arcopilus macrostiolatus (Stchigel et al.) X.Wei Wang & Houbraken, Arcopilus megasporus (Sörgel ex Seth) X.Wei Wang & Houbraken, Arcopilus purpurascens (Udagawa & Y. Sugiy.) X.Wei Wang & Houbraken, Arxotrichum deceptivum (Malloch & Benny) X.Wei Wang & Houbraken, Arxotrichum gangligerum (L.M. Ames) X.Wei Wang & Houbraken, Arxotrichum officinarum (M. Raza & L. Cai) X.Wei Wang & Houbraken, Arxotrichum piluliferoides (Udagawa & Y. Horie) X.Wei Wang & Houbraken, Arxotrichum repens (Guarro & Figueras) X.Wei Wang & Houbraken, Arxotrichum sinense (K.T. Chen) X.Wei Wang & Houbraken, Botryotrichum inquinatum (Udagawa & S. Ueda) X.Wei Wang & Houbraken, Botryotrichum retardatum (A. Carter & R.S. Khan) X.Wei Wang & Houbraken, Botryotrichum trichorobustum (Seth) X.Wei Wang & Houbraken, Botryotrichum vitellinum (A. Carter) X.Wei Wang & Houbraken, Collariella anguipilia (L.M. Ames) X.Wei Wang & Houbraken, Collariella hexagonospora (A. Carter & Malloch) X.Wei Wang & Houbraken, Collariella pachypodioides (L.M. Ames) X.Wei Wang & Houbraken, Ovatospora amygdalispora (Udagawa & T. Muroi) X.Wei Wang & Houbraken, Ovatospora angularis (Yu Zhang & L. Cai) X.Wei Wang & Houbraken, Parachaetomium biporatum (Cano & Guarro) X.Wei Wang & Houbraken, Parachaetomium hispanicum (Guarro & Arx) X.Wei Wang & Houbraken, Parachaetomium inaequale (Pidopl. et al.) X.Wei Wang & Houbraken, Parachaetomium longiciliatum (Yu Zhang & L. Cai) X.Wei Wang & Houbraken, Parachaetomium mareoticum (Besada & Yusef) X.Wei Wang & Houbraken, Parachaetomium muelleri (Arx) X.Wei Wang & Houbraken, Parachaetomium multispirale (A. Carter et al.) X.Wei Wang & Houbraken, Parachaetomium perlucidum (Sergejeva) X.Wei Wang & Houbraken, Parachaetomium subspirilliferum (Sergejeva) X.Wei Wang & Houbraken, Parathielavia coactilis (Nicot) X.Wei Wang & Houbraken, Parvomelanocarpus tardus (X.Wei Wang & Samson) X.Wei Wang & Houbraken, Parvomelanocarpus thermophilus (Abdullah & Al-Bader) X.Wei Wang & Houbraken, Pseudohumicola atrobrunnea (X.Wei Wang et al.) X.Wei Wang, P.J. Han, F.Y. Bai & Houbraken, Pseudohumicola pulvericola (X.Wei Wang et al.) X.Wei Wang, P.J. Han, F.Y. Bai & Houbraken, Pseudohumicola semispiralis (Udagawa & Cain) X.Wei Wang, P.J. Han, F.Y. Bai & Houbraken, Pseudohumicola subspiralis (Chivers) X.Wei Wang, P.J. Han, F.Y. Bai & Houbraken, Staphylotrichum koreanum (Hyang B. Lee & T.T.T. Nguyen) X.Wei Wang & Houbraken, Staphylotrichum limonisporum (Z.F. Zhang & L. Cai) X.Wei Wang & Houbraken, Subramaniula lateralis (Yu Zhang & L. Cai) X.Wei Wang & Houbraken, Thermocarpiscus australiensis (Tansey & M.A. Jack) X.Wei Wang & Houbraken, Thermochaetoides dissita (Cooney & R. Emers.) X.Wei Wang & Houbraken, Thermochaetoides thermophila (La Touche) X.Wei Wang & Houbraken, Xanthiomyces spinosus (Chivers) X.Wei Wang & Houbraken; New names: Chaetomium neoglobosporum X.Wei Wang & Houbraken, Thermothelomyces fergusii X.Wei Wang & Houbraken, Thermothelomyces myriococcoides X.Wei Wang & Houbraken; Lecto- and / or epi-typifications (basionyms): Botryoderma rostratum Papendorf & H.P. Upadhyay, Botryotrichum piluliferum Sacc. & Marchal, Chaetomium carinthiacum Sörgel, Thielavia heterothallica Klopotek. Citation: Wang XW, Han PJ, Bai FY, Luo A, Bensch K, Meijer M, Kraak B, Han DY, Sun BD, Crous PW, Houbraken J (2022). Taxonomy, phylogeny and identification of Chaetomiaceae with emphasis on thermophilic species. Studies in Mycology 101: 121-243. doi: 10.3114/sim.2022.101.03.

Fusarium: more than a node or a foot-shaped basal cell.

Recent publications have argued that there are potentially serious consequences for researchers in recognising distinct genera in the terminal fusarioid clade of the family Nectriaceae. Thus, an alternate hypothesis, namely a very broad concept of the genus Fusarium was proposed. In doing so, however, a significant body of data that supports distinct genera in Nectriaceae based on morphology, biology, and phylogeny is disregarded. A DNA phylogeny based on 19 orthologous protein-coding genes was presented to support a very broad concept of Fusarium at the F1 node in Nectriaceae. Here, we demonstrate that re-analyses of this dataset show that all 19 genes support the F3 node that represents Fusarium sensu stricto as defined by F. sambucinum (sexual morph synonym Gibberella pulicaris). The backbone of the phylogeny is resolved by the concatenated alignment, but only six of the 19 genes fully support the F1 node, representing the broad circumscription of Fusarium. Furthermore, a re-analysis of the concatenated dataset revealed alternate topologies in different phylogenetic algorithms, highlighting the deep divergence and unresolved placement of various Nectriaceae lineages proposed as members of Fusarium. Species of Fusarium s. str. are characterised by Gibberella sexual morphs, asexual morphs with thin- or thick-walled macroconidia that have variously shaped apical and basal cells, and trichothecene mycotoxin production, which separates them from other fusarioid genera. Here we show that the Wollenweber concept of Fusarium presently accounts for 20 segregate genera with clear-cut synapomorphic traits, and that fusarioid macroconidia represent a character that has been gained or lost multiple times throughout Nectriaceae. Thus, the very broad circumscription of Fusarium is blurry and without apparent synapomorphies, and does not include all genera with fusarium-like macroconidia, which are spread throughout Nectriaceae (e.g., Cosmosporella, Macroconia, Microcera). In this study four new genera are introduced, along with 18 new species and 16 new combinations. These names convey information about relationships, morphology, and ecological preference that would otherwise be lost in a broader definition of Fusarium. To assist users to correctly identify fusarioid genera and species, we introduce a new online identification database, Fusarioid-ID, accessible at www.fusarium.org. The database comprises partial sequences from multiple genes commonly used to identify fusarioid taxa (act1, CaM, his3, rpb1, rpb2, tef1, tub2, ITS, and LSU). In this paper, we also present a nomenclator of names that have been introduced in Fusarium up to January 2021 as well as their current status, types, and diagnostic DNA barcode data. In this study, researchers from 46 countries, representing taxonomists, plant pathologists, medical mycologists, quarantine officials, regulatory agencies, and students, strongly support the application and use of a more precisely delimited Fusarium (= Gibberella) concept to accommodate taxa from the robust monophyletic node F3 on the basis of a well-defined and unique combination of morphological and biochemical features. This F3 node includes, among others, species of the F. fujikuroi, F. incarnatum-equiseti, F. oxysporum, and F. sambucinum species complexes, but not species of Bisifusarium [F. dimerum species complex (SC)], Cyanonectria (F. buxicola SC), Geejayessia (F. staphyleae SC), Neocosmospora (F. solani SC) or Rectifusarium (F. ventricosum SC). The present study represents the first step to generating a new online monograph of Fusarium and allied fusarioid genera (www.fusarium.org).

A new species concept for the clinically relevant Mucor circinelloides complex.

Mucor species are common soil fungi but also known as agents of human infections (mucormycosis) and used in food production and biotechnology. Mucor circinelloides is the Mucor species that is most frequently isolated from clinical sources. The taxonomy of Mucor circinelloides and its close relatives (Mucor circinelloides complex - MCC) is still based on morphology and mating behaviour. The aim of the present study was a revised taxonomy of the MCC using a polyphasic approach. Using a set of 100 strains molecular phylogenetic analysis of five markers (ITS, rpb1, tsr1, mcm7, and cfs, introduced here) were performed, combined with phenotypic studies, mating tests and the determination of the maximum growth temperatures. The multi-locus analyses revealed 16 phylogenetic species of which 14 showed distinct phenotypical traits and were recognised as discrete species. Five of these species are introduced as novel taxa: M. amethystinus sp. nov., M. atramentarius sp. nov., M. variicolumellatus sp. nov., M. pseudocircinelloides sp. nov., and M. pseudolusitanicus sp. nov. The former formae of M. circinelloides represent one or two separate species. In the MCC, the simple presence of well-shaped zygospores only indicates a close relation of both strains, but not necessarily conspecificity. Seven species of the MCC have been implemented in human infection: M. circinelloides, M. griseocyanus, M. janssenii, M. lusitanicus, M. ramosissimus, M. variicolumellatus, and M. velutinosus.

Classification of Aspergillus, Penicillium, Talaromyces and related genera (Eurotiales): An overview of families, genera, subgenera, sections, series and species.

The Eurotiales is a relatively large order of Ascomycetes with members frequently having positive and negative impact on human activities. Species within this order gain attention from various research fields such as food, indoor and medical mycology and biotechnology. In this article we give an overview of families and genera present in the Eurotiales and introduce an updated subgeneric, sectional and series classification for Aspergillus and Penicillium. Finally, a comprehensive list of accepted species in the Eurotiales is given. The classification of the Eurotiales at family and genus level is traditionally based on phenotypic characters, and this classification has since been challenged using sequence-based approaches. Here, we re-evaluated the relationships between families and genera of the Eurotiales using a nine-gene sequence dataset. Based on this analysis, the new family Penicillaginaceae is introduced and four known families are accepted: Aspergillaceae, Elaphomycetaceae, Thermoascaceae and Trichocomaceae. The Eurotiales includes 28 genera: 15 genera are accommodated in the Aspergillaceae (Aspergillago, Aspergillus, Evansstolkia, Hamigera, Leiothecium, Monascus, Penicilliopsis, Penicillium, Phialomyces, Pseudohamigera, Pseudopenicillium, Sclerocleista, Warcupiella, Xerochrysium and Xeromyces), eight in the Trichocomaceae (Acidotalaromyces, Ascospirella, Dendrosphaera, Rasamsonia, Sagenomella, Talaromyces, Thermomyces, Trichocoma), two in the Thermoascaceae (Paecilomyces, Thermoascus) and one in the Penicillaginaceae (Penicillago). The classification of the Elaphomycetaceae was not part of this study, but according to literature two genera are present in this family (Elaphomyces and Pseudotulostoma). The use of an infrageneric classification system has a long tradition in Aspergillus and Penicillium. Most recent taxonomic studies focused on the sectional level, resulting in a well-established sectional classification in these genera. In contrast, a series classification in Aspergillus and Penicillium is often outdated or lacking, but is still relevant, e.g., the allocation of a species to a series can be highly predictive in what functional characters the species might have and might be useful when using a phenotype-based identification. The majority of the series in Aspergillus and Penicillium are invalidly described and here we introduce a new series classification. Using a phylogenetic approach, often supported by phenotypic, physiologic and/or extrolite data, Aspergillus is subdivided in six subgenera, 27 sections (five new) and 75 series (73 new, one new combination), and Penicillium in two subgenera, 32 sections (seven new) and 89 series (57 new, six new combinations). Correct identification of species belonging to the Eurotiales is difficult, but crucial, as the species name is the linking pin to information. Lists of accepted species are a helpful aid for researchers to obtain a correct identification using the current taxonomic schemes. In the most recent list from 2014, 339 Aspergillus, 354 Penicillium and 88 Talaromyces species were accepted. These numbers increased significantly, and the current list includes 446 Aspergillus (32 % increase), 483 Penicillium (36 % increase) and 171 Talaromyces (94 % increase) species, showing the large diversity and high interest in these genera. We expanded this list with all genera and species belonging to the Eurotiales (except those belonging to Elaphomycetaceae). The list includes 1 187 species, distributed over 27 genera, and contains MycoBank numbers, collection numbers of type and ex-type cultures, subgenus, section and series classification data, information on the mode of reproduction, and GenBank accession numbers of ITS, beta-tubulin (BenA), calmodulin (CaM) and RNA polymerase II second largest subunit (RPB2) gene sequences.

Diversity and phylogeny of basidiomycetous yeasts from plant leaves and soil: Proposal of two new orders, three new families, eight new genera and one hundred and seven new species.

Nearly 500 basidiomycetous yeast species were accepted in the latest edition of The Yeasts: A Taxonomic Study published in 2011. However, this number presents only the tip of the iceberg of yeast species diversity in nature. Possibly more than 99 % of yeast species, as is true for many groups of fungi, are yet unknown and await discovery. Over the past two decades nearly 200 unidentified isolates were obtained during a series of environmental surveys of yeasts in phyllosphere and soils, mainly from China. Among these isolates, 107 new species were identified based on the phylogenetic analyses of nuclear ribosomal DNA (rDNA) [D1/D2 domains of the large subunit (LSU), the small subunit (SSU), and the internal transcribed spacer region including the 5.8S rDNA (ITS)] and protein-coding genes [both subunits of DNA polymerase II (RPB1 and RPB2), the translation elongation factor 1-α (TEF1) and the mitochondrial gene cytochrome b (CYTB)], and physiological comparisons. Forty-six of these belong to 16 genera in the Tremellomycetes (Agaricomycotina). The other 61 are distributed in 26 genera in the Pucciniomycotina. Here we circumscribe eight new genera, three new families and two new orders based on the multi-locus phylogenetic analyses combined with the clustering optimisation analysis and the predicted similarity thresholds for yeasts and filamentous fungal delimitation at genus and higher ranks. Additionally, as a result of these analyses, three new combinations are proposed and 66 taxa are validated.

Phylogenetic re-evaluation of Thielavia with the introduction of a new family Podosporaceae.

The genus Thielavia is morphologically defined by having non-ostiolate ascomata with a thin peridium composed of textura epidermoidea, and smooth, single-celled, pigmented ascospores with one germ pore. Thielavia is typified with Th. basicola that grows in close association with a hyphomycete which was traditionally identified as Thielaviopsis basicola. Besides Th. basicola exhibiting the mycoparasitic nature, the majority of the described Thielavia species are from soil, and some have economic and ecological importance. Unfortunately, no living type material of Th. basicola exists, hindering a proper understanding of the classification of Thielavia. Therefore, Thielavia basicola was neotypified by material of a mycoparasite presenting the same ecology and morphology as described in the original description. We subsequently performed a multi-gene phylogenetic analyses (rpb2, tub2, ITS and LSU) to resolve the phylogenetic relationships of the species currently recognised in Thielavia. Our results demonstrate that Thielavia is highly polyphyletic, being related to three family-level lineages in two orders. The redefined genus Thielavia is restricted to its type species, Th. basicola, which belongs to the Ceratostomataceae (Melanosporales) and its host is demonstrated to be Berkeleyomyces rouxiae, one of the two species in the "Thielaviopsis basicola" species complex. The new family Podosporaceae is sister to the Chaetomiaceae in the Sordariales and accommodates the re-defined genera Podospora, Trangularia and Cladorrhinum, with the last genus including two former Thielavia species (Th. hyalocarpa and Th. intermedia). This family also includes the genetic model species Podospora anserina, which was combined in Triangularia (as Triangularia anserina). The remaining Thielavia species fall in ten unrelated clades in the Chaetomiaceae, leading to the proposal of nine new genera (Carteria, Chrysanthotrichum, Condenascus, Hyalosphaerella, Microthielavia, Parathielavia, Pseudothielavia, Stolonocarpus and Thermothielavioides). The genus Canariomyces is transferred from Microascaceae (Microascales) to Chaetomiaceae based on its type species Can. notabilis. Canariomyces is closely related to the human-pathogenic genus Madurella, and includes three thielavia-like species and one novel species. Three monotypic genera with a chaetomium-like morph (Brachychaeta, Chrysocorona and Floropilus) are introduced to better resolve the Chaetomiaceae and the thielavia-like species in the family. Chrysocorona lucknowensis and Brachychaeta variospora are closely related to Acrophialophora and three newly introduced genera containing thielavia-like species; Floropilus chiversii is closely related to the industrially important and thermophilic species Thermothielavioides terrestris (syn. Th. terrestris). This study shows that the thielavia-like morph is a homoplastic form that originates from several separate evolutionary events. Furthermore, our results provide new insights into the taxonomy of Sordariales and the polyphyletic Lasiosphaeriaceae.

Signatures of a jet cocoon in early spectra of a supernova associated with a γ-ray burst.

Long γ-ray bursts are associated with energetic, broad-lined, stripped-envelope supernovae1,2 and as such mark the death of massive stars. The scarcity of such events nearby and the brightness of the γ-ray burst afterglow, which dominates the emission in the first few days after the burst, have so far prevented the study of the very early evolution of supernovae associated with γ-ray bursts3. In hydrogen-stripped supernovae that are not associated with γ-ray bursts, an excess of high-velocity (roughly 30,000 kilometres per second) material has been interpreted as a signature of a choked jet, which did not emerge from the progenitor star and instead deposited all of its energy in a thermal cocoon4. Here we report multi-epoch spectroscopic observations of the supernova SN 2017iuk, which is associated with the γ-ray burst GRB 171205A. Our spectra display features at extremely high expansion velocities (around 115,000 kilometres per second) within the first day after the burst5,6. Using spectral synthesis models developed for SN 2017iuk, we show that these features are characterized by chemical abundances that differ from those observed in the ejecta of SN 2017iuk at later times. We further show that the high-velocity features originate from the mildly relativistic hot cocoon that is generated by an ultra-relativistic jet within the γ-ray burst expanding and decelerating into the medium that surrounds the progenitor star7,8. This cocoon rapidly becomes transparent9 and is outshone by the supernova emission, which starts to dominate the emission three days after the burst.

Cladosporium species in indoor environments.

As part of a worldwide survey of the indoor mycobiota about 520 new Cladosporium isolates from indoor environments mainly collected in China, Europe, New Zealand, North America and South Africa were investigated by using a polyphasic approach to determine their species identity. All Cladosporium species occurring in indoor environments are fully described and illustrated. Fourty-six Cladosporium species are treated of which 16 species are introduced as new. A key for the most common Cladosporium species isolated from indoor environments is provided. Cladosporium halotolerans proved to be the most frequently isolated Cladosporium species indoors.

Genera of phytopathogenic fungi: GOPHY 1.

Genera of Phytopathogenic Fungi (GOPHY) is introduced as a new series of publications in order to provide a stable platform for the taxonomy of phytopathogenic fungi. This first paper focuses on 21 genera of phytopathogenic fungi: Bipolaris, Boeremia, Calonectria, Ceratocystis, Cladosporium, Colletotrichum, Coniella, Curvularia, Monilinia, Neofabraea, Neofusicoccum, Pilidium, Pleiochaeta, Plenodomus, Protostegia, Pseudopyricularia, Puccinia, Saccharata, Thyrostroma, Venturia and Wilsonomyces. For each genus, a morphological description and information about its pathology, distribution, hosts and disease symptoms are provided. In addition, this information is linked to primary and secondary DNA barcodes of the presently accepted species, and relevant literature. Moreover, several novelties are introduced, i.e. new genera, species and combinations, and neo-, lecto- and epitypes designated to provide a stable taxonomy. This first paper includes one new genus, 26 new species, ten new combinations, and four typifications of older names.

Neoadjuvant chemoradiotherapy with concurrent cisplatin/5-fluorouracil is associated with increased pathologic complete response and improved survival compared to carboplatin/paclitaxel in patients with locally advanced esophageal cancer.

Trimodal therapy consisting of neoadjuvant chemoradiation followed by esophagectomy has become the standard of care in North America for locally advanced esophageal cancer. While cisplatin/5-fluorouracil has been a common concurrent chemotherapy regimen since the 1980s, its utilization has declined in recent years as the Chemoradiotherapy for Oesophageal Cancer Followed by Surgery Study (CROSS) trial regimen of carboplatin/paclitaxel has become widely adopted. The efficacy of the CROSS regimen compared to alternate chemotherapy choices, however, has rarely been evaluated when each is used as a component of a trimodal treatment approach. The aim of this study is to report our institutional experience with these two concurrent chemotherapy regimens at a specialized esophageal cancer center.We performed an Institutional Review Board-approved retrospective review of a prospectively maintained institutional foregut registry from a single National Cancer Institute-designated cancer center. Esophageal cancer patients who completed trimodal therapy with a chemotherapy regimen of either carboplatin/paclitaxel or cisplatin/5-fluorouracil were identified and divided into groups based on their chemotherapy regimens. Multivariable logistic regression was used to analyze pathologic complete response rates, while the Kaplan-Meier and Cox proportional hazards models were utilized to evaluate recurrence-free and overall survival. Analytical models were adjusted for age, clinical stage, radiation dose, histologic subtype (adenocarcinoma vs. squamous cell carcinoma), and time interval from completion of neoadjuvant therapy to surgery.One hundred and forty-two patients treated between January of 2000 and July of 2015 were identified as meeting inclusion criteria. Of this group, 87 had received the CROSS regimen of carboplatin/paclitaxel, while 55 had completed cisplatin/5-fluorouracil. Multivariable analysis demonstrated that the cisplatin/5-fluorouracil.group had an increased odds of pathologic complete response (odds ratio = 2.68, 95% confidence interval, P = 0.032), as well as significantly improved recurrence-free survival (hazard ratio = 0.39, 95% confidence interval 0.21-0.73, P = 0.003) and overall survival (hazard ratio = 0.46, 95% confidence interval 0.24-0.87, P = 0.016), compared to the carboplatin/paclitaxel group.Concurrent chemotherapy with cisplatin/5-fluorouracil in locally advanced esophageal cancer is associated with higher rates of pathologic complete response and improved recurrence-free and overall survival compared to the CROSS regimen of carboplatin/paclitaxel. This suggests that, for select patients, alternate neoadjuvant chemotherapy approaches, such as cisplatin/5-fluorouracil, merit reconsideration as potential primary treatment choices in the management of this highly morbid disease.

Common but different: The expanding realm of Cladosporium.

The genus Cladosporium (Cladosporiaceae, Dothideomycetes), which represents one of the largest genera of dematiaceous hyphomycetes, has been intensively investigated during the past decade. In the process, three major species complexes (C. cladosporioides, C. herbarum and C. sphaerospermum) were resolved based on morphology and DNA phylogeny, and a monographic revision of the genus (s. lat.) published reflecting the current taxonomic status quo. In the present study a further 19 new species are described based on phylogenetic characters (nuclear ribosomal RNA gene operon, including the internal transcribed spacer regions ITS1 and ITS2, as well as partial actin and translation elongation factor 1-α gene sequences) and morphological differences. For a selection of the species with ornamented conidia, scanning electron microscopic photos were prepared to illustrate the different types of surface ornamentation. Surprisingly, during this study Cladosporium ramotenellum was found to be a quite common saprobic species, being widely distributed and occurring on various substrates. Therefore, an emended species description is provided. Furthermore, the host range and distribution data for several previously described species are also expanded.

The genus Cladosporium.

A monographic revision of the hyphomycete genus Cladosporium s. lat. (Cladosporiaceae, Capnodiales) is presented. It includes a detailed historic overview of Cladosporium and allied genera, with notes on their phylogeny, systematics and ecology. True species of Cladosporium s. str. (anamorphs of Davidiella), are characterised by having coronate conidiogenous loci and conidial hila, i.e., with a convex central dome surrounded by a raised periclinal rim. Recognised species are treated and illustrated with line drawings and photomicrographs (light as well as scanning electron microscopy). Species known from culture are described in vivo as well as in vitro on standardised media and under controlled conditions. Details on host range/substrates and the geographic distribution are given based on published accounts, and a re-examination of numerous herbarium specimens. Various keys are provided to support the identification of Cladosporium species in vivo and in vitro. Morphological datasets are supplemented by DNA barcodes (nuclear ribosomal RNA gene operon, including the internal transcribed spacer regions ITS1 and ITS2, the 5.8S nrDNA, as well as partial actin and translation elongation factor 1-α gene sequences) diagnostic for individual species. In total 993 names assigned to Cladosporium s. lat., including Heterosporium (854 in Cladosporium and 139 in Heterosporium), are treated, of which 169 are recognized in Cladosporium s. str. The other taxa are doubtful, insufficiently known or have been excluded from Cladosporium in its current circumscription and re-allocated to other genera by the authors of this monograph or previous authors. TAXONOMIC NOVELTIES: Cladosporium allicinum (Fr.: Fr.) Bensch, U. Braun & Crous, comb. nov., C. astroideum var. catalinense U. Braun, var. nov., Fusicladium tectonicola (Yong H. He & Z.Y. Zhang) U. Braun & Bensch, comb. nov., Septoidium uleanum (Henn.) U. Braun, comb. nov., Zasmidium adeniae (Hansf.) U. Braun, comb. nov., Zasmidium dianellae (Sawada & Katsuki) U. Braun, comb. nov., Zasmidium lythri (Westend.) U. Braun & H.D. Shin, comb. nov., Zasmidium wikstroemiae (Petch) U. Braun, comb. nov.

Investigations into the antiadhesive activity of herbal extracts against Campylobacter jejuni.

Campylobacter jejuni is one of the most common bacterial causes of diarrhoea in the industrialized world, being associated with the occurrence of Guillain-Barré Syndrome, and inducing diseases partially through intestinal adherence. With increasing reports of C. jejuni drug resistance against standard antibiotics, investigations into antiadhesive agents for the prevention of bacterial infection are highly significant. Given the consumer-driven development towards holistic and integrative healthcare, research into additional anti-Campylobacter effects of herbal medicines that are already used for their beneficial effects on bowel and digestive functions is important. Twenty-one herbal extracts were screened for antiadhesive activity against C. jejuni using modifications of previously published antiadhesion assays. Antiadhesion effects with IC(50) values <3 mg/mL were obtained for seven ethanol plant extracts, with Zingiber officinale (ginger), Capsicum annum (cayenne) and Glycyrrhiza glabra (licorice) displaying the highest antiadhesion activity against C. jejuni (IC(50) : <0.1 mg/mL, 0.29 mg/mL and 0.65 mg/mL, respectively). Differences in antiadhesion activity were found for two different Echinacea species, with E. purpurea displaying significantly higher and dose dependent antiadhesion activity than E. angustifolia. No significant antiadhesion activity (IC(50) values >35 mg/mL) was found for Agrimonia eupatoria (agrimony), Andrographis paniculata (andrographis), Matricaria recutita (chamomile), Foeniculum vulgare (fennel), Filipendula ulmaria (meadowsweet) and Artemisia absinthium (wormwood) extracts. This study provides evidence for additional beneficial effects of marketed herbal medicines in gastrointestinal disorders.

Species and ecological diversity within the Cladosporium cladosporioides complex (Davidiellaceae, Capnodiales).

The genus Cladosporium is one of the largest genera of dematiaceous hyphomycetes, and is characterised by a coronate scar structure, conidia in acropetal chains and Davidiella teleomorphs. Based on morphology and DNA phylogeny, the species complexes of C. herbarum and C. sphaerospermum have been resolved, resulting in the elucidation of numerous new taxa. In the present study, more than 200 isolates belonging to the C. cladosporioides complex were examined and phylogenetically analysed on the basis of DNA sequences of the nuclear ribosomal RNA gene operon, including the internal transcribed spacer regions ITS1 and ITS2, the 5.8S nrDNA, as well as partial actin and translation elongation factor 1-α gene sequences. For the saprobic, widely distributed species Cladosporium cladosporioides, both a neotype and epitype are designated in order to specify a well established circumscription and concept of this species. Cladosporium tenuissimum and C. oxysporum, two saprobes abundant in the tropics, are epitypified and shown to be allied to, but distinct from C. cladosporioides. Twenty-two species are newly described on the basis of phylogenetic characters and cryptic morphological differences. The most important phenotypic characters for distinguishing species within the C. cladosporioides complex, which represents a monophyletic subclade within the genus, are shape, width, length, septation and surface ornamentation of conidia and conidiophores; length and branching patterns of conidial chains and hyphal shape, width and arrangement. Many of the treated species, e.g., C. acalyphae, C. angustisporum, C. australiense, C. basiinflatum, C. chalastosporoides, C. colocasiae, C. cucumerinum, C. exasperatum, C. exile, C. flabelliforme, C. gamsianum, and C. globisporum are currently known only from specific hosts, or have a restricted geographical distribution. A key to all species recognised within the C. cladosporioides complex is provided.

A transgenic model to study the pathogenesis of somatic mtDNA mutation accumulation in beta-cells.

Low levels of somatic mutations accumulate in mitochondrial DNA (mtDNA) as we age; however, the pathogenic nature of these mutations is unknown. In contrast, mutational loads of >30% of mtDNA are associated with electron transport chain defects that result in mitochondrial diseases such as mitochondrial encephalopathy lactic acidosis and stroke-like episodes. Pancreatic beta-cells may be extremely sensitive to the accumulation of mtDNA mutations, as insulin secretion requires the mitochondrial oxidation of glucose to CO(2). Type 2 diabetes arises when beta-cells fail to compensate for the increased demand for insulin, and many type 2 diabetics progress to insulin dependence because of a loss of beta-cell function or beta-cell death. This loss of beta-cell function/beta-cell death has been attributed to the toxic effects of elevated levels of lipids and glucose resulting in the enhanced production of free radicals in beta-cells. mtDNA, localized in close proximity to one of the major cellular sites of free radical production, comprises more than 95% coding sequences such that mutations result in changes in the coding sequence. It has long been known that mtDNA mutations accumulate with age; however, only recently have studies examined the influence of somatic mtDNA mutation accumulation on disease pathogenesis. This article will focus on the effects of low-level somatic mtDNA mutation accumulation on ageing, cardiovascular disease and diabetes.

Acid resistance of Helicobacter pylori depends on the UreI membrane protein and an inner membrane proton barrier.

ureI encodes an inner membrane protein of Helicobacter pylori. The role of the bacterial inner membrane and UreI in acid protection and regulation of cytoplasmic urease activity in the gastric microorganism was studied. The irreversible inhibition of urease when the organism was exposed to a protonophore (3,3',4', 5-tetrachlorsalicylanide; TCS) at acidic pH showed that the inner membrane protected urease from acid. Isogenic ureI knockout mutants of several H. pylori strains were constructed by replacing the ureI gene of the urease gene cluster with a promoterless kanamycin resistance marker gene (kanR). Mutants carrying the modified ureAB-kanR-EFGH operon all showed wild-type levels of urease activity at neutral pH in vitro. The mutants resisted media of pH > 4.0 but not of pH < 4.0. Whereas wild-type bacteria showed high levels of urease activity below pH 4.0, this ability was not retained in the ureI mutants, resulting in inhibition of metabolism and cell death. Gene complementation experiments with plasmid-derived H. pylori ureI restored wild-type properties. The activation of urease activity found in structurally intact but permeabilized bacteria treated with 0.01% detergent (polyoxy-ethylene-8-laurylether; C12E8), suggested a membrane-limited access of urea to internal urease at neutral pH. Measurement of 14C-urea uptake into Xenopus oocytes injected with ureI cRNA showed acid activation of uptake only in injected oocytes. Acceleration of urea uptake by UreI therefore mediates the increase of intracellular urease activity seen under acidic conditions. This increase of urea permeability is essential for H. pylori survival in environments below pH 4.0. ureI-independent urease activity may be sufficient for maintenance of bacterial viability above pH 4.0.