Hyphal compartmentalization and sporulation in Streptomyces require the conserved cell division protein SepX.

Filamentous actinobacteria such as Streptomyces undergo two distinct modes of cell division, leading to partitioning of growing hyphae into multicellular compartments via cross-walls, and to septation and release of unicellular spores. Specific determinants for cross-wall formation and the importance of hyphal compartmentalization for Streptomyces development are largely unknown. Here we show that SepX, an actinobacterial-specific protein, is crucial for both cell division modes in Streptomyces venezuelae. Importantly, we find that sepX-deficient mutants grow without cross-walls and that this substantially impairs the fitness of colonies and the coordinated progression through the developmental life cycle. Protein interaction studies and live-cell imaging suggest that SepX contributes to the stabilization of the divisome, a mechanism that also requires the dynamin-like protein DynB. Thus, our work identifies an important determinant for cell division in Streptomyces that is required for cellular development and sporulation.

Habitat geometry in artificial microstructure affects bacterial and fungal growth, interactions, and substrate degradation.

Microhabitat conditions determine the magnitude and speed of microbial processes but have been challenging to investigate. In this study we used microfluidic devices to determine the effect of the spatial distortion of a pore space on fungal and bacterial growth, interactions, and substrate degradation. The devices contained channels differing in bending angles and order. Sharper angles reduced fungal and bacterial biomass, especially when angles were repeated in the same direction. Substrate degradation was only decreased by sharper angles when fungi and bacteria were grown together. Investigation at the cellular scale suggests that this was caused by fungal habitat modification, since hyphae branched in sharp and repeated turns, blocking the dispersal of bacteria and the substrate. Our results demonstrate how the geometry of microstructures can influence microbial activity. This can be transferable to soil pore spaces, where spatial occlusion and microbial feedback on microstructures is thought to explain organic matter stabilization.

Candida albicans ENT2 Contributes to Efficient Endocytosis, Cell Wall Integrity, Filamentation, and Virulence.

Epsins play a pivotal role in the formation of endocytic vesicles and potentially provide a linkage between endocytic and other trafficking pathways. We identified a Candida albicans epsin, ENT2, that bears homology to the Saccharomyces cerevisiae early endocytosis genes ENT1 and ENT2 and studied its functions by a reverse genetic approach utilizing CRISPR-Cas9-mediated gene deletion. The C. albicans ent2Δ/Δ null mutant displayed cell wall defects and altered antifungal drug sensitivity. To define the role of C. albicans ENT2 in endocytosis, we performed assays with the lipophilic dye FM4-64 that revealed greatly reduced uptake in the ent2Δ/Δ mutant. Next, we showed that the C. albicans ent2Δ/Δ mutant was unable to form hyphae and biofilms. Assays for virulence properties in an in vitro keratinocyte infection model demonstrated reduced damage of mammalian adhesion zippers and host cell death from the ent2Δ/Δ mutant. We conclude that C. albicans ENT2 has a role in efficient endocytosis, a process that is required for maintaining cell wall integrity, hyphal formation, and virulence-defining traits. IMPORTANCE The opportunistic fungal pathogen Candida albicans is an important cause of invasive infections in hospitalized patients and a source of considerable morbidity and mortality. Despite its clinical importance, we still need to improve our ability to diagnose and treat this common pathogen. In order to support these advancements, a greater understanding of the biology of C. albicans is needed. In these studies, we are focused on the fundamental biological process of endocytosis, of which little is directly known in C. albicans. In addition to studying the function of a key gene in this process, we are examining the role of endocytosis in the virulence-related processes of filamentation, biofilm formation, and tissue invasion. These studies will provide greater insight into the role of endocytosis in causing invasive fungal infections.

Immune cells fold and damage fungal hyphae.

Innate immunity provides essential protection against life-threatening fungal infections. However, the outcomes of individual skirmishes between immune cells and fungal pathogens are not a foregone conclusion because some pathogens have evolved mechanisms to evade phagocytic recognition, engulfment, and killing. For example, Candida albicans can escape phagocytosis by activating cellular morphogenesis to form lengthy hyphae that are challenging to engulf. Through live imaging of C. albicans-macrophage interactions, we discovered that macrophages can counteract this by folding fungal hyphae. The folding of fungal hyphae is promoted by Dectin-1, ß2-integrin, VASP, actin-myosin polymerization, and cell motility. Folding facilitates the complete engulfment of long hyphae in some cases and it inhibits hyphal growth, presumably tipping the balance toward successful fungal clearance.

Trade-off between Plasticity and Velocity in Mycelial Growth.

Tip-growing fungal cells maintain cell polarity at the apical regions and elongate by de novo synthesis of the cell wall. Cell polarity and tip growth rate affect mycelial morphology. However, it remains unclear how both features act cooperatively to determine cell shape. Here, we investigated this relationship by analyzing hyphal tip growth of filamentous fungi growing inside extremely narrow 1 µm-width channels of microfluidic devices. Since the channels are much narrower than the diameter of hyphae, any hypha growing through the channel must adapt its morphology. Live-cell imaging analyses revealed that hyphae of some species continued growing through the channels, whereas hyphae of other species often ceased growing when passing through the channels, or had lost apical polarity after emerging from the other end of the channel. Fluorescence live-cell imaging analyses of the Spitzenkörper, a collection of secretory vesicles and polarity-related proteins at the hyphal tip, in Neurospora crassa indicates that hyphal tip growth requires a very delicate balance of ordered exocytosis to maintain polarity in spatially confined environments. We analyzed the mycelial growth of seven fungal species from different lineages, including phytopathogenic fungi. This comparative approach revealed that the growth defects induced by the channels were not correlated with their taxonomic classification or with the width of hyphae, but, rather, correlated with the hyphal elongation rate. This report indicates a trade-off between morphological plasticity and velocity in mycelial growth and serves to help understand fungal invasive growth into substrates or plant/animal cells, with direct impact on fungal biotechnology, ecology, and pathogenicity.IMPORTANCE Cell morphology, which is controlled by polarity and growth, is fundamental for all cellular functions. However how polarity and growth act cooperatively to control cell shape remains unclear. Here we investigated their relationship by analyzing hyphal tip growth of filamentous fungi growing inside extremely narrow 1 µm-width channels of microfluidic devices. We found that most fast growing hyphae often lost the cell polarity after emerging from the channels, whereas slow growing hyphae retained polarity and continued growing, indicating a trade-off between plasticity and velocity in mycelial growth. These results serve to understand fungal invasive growth into substrates or plant/animal cells, with direct impact on fungal biotechnology, ecology and pathogenicity.

Dispersal of Arbuscular Mycorrhizal Fungi: Evidence and Insights for Ecological Studies.

Dispersal is a critical ecological process that modulates gene flow and contributes to the maintenance of genetic and taxonomic diversity within ecosystems. Despite an increasing global understanding of the arbuscular mycorrhizal (AM) fungal diversity, distribution and prevalence in different biomes, we have largely ignored the main dispersal mechanisms of these organisms. To provide a geographical and scientific overview of the available data, we systematically searched for the direct evidence on the AM fungal dispersal agents (abiotic and biotic) and different propagule types (i.e. spores, extraradical hyphae or colonized root fragments). We show that the available data (37 articles) on AM fungal dispersal originates mostly from North America, from temperate ecosystems, from biotic dispersal agents (small mammals) and AM fungal spores as propagule type. Much lesser evidence exists from South American, Asian and African tropical systems and other dispersers such as large-bodied birds and mammals and non-spore propagule types. We did not find strong evidence that spore size varies across dispersal agents, but wind and large animals seem to be more efficient dispersers. However, the data is still too scarce to draw firm conclusions from this finding. We further discuss and propose critical research questions and potential approaches to advance the understanding of the ecology of AM fungi dispersal.

Fungal Wound Healing through Instantaneous Protoplasmic Gelation.

Multicellular organisms employ fluid transport networks to overcome the limit of diffusion and promote essential long-distance transport. Connectivity and pressurization render these networks especially vulnerable to wounding. To mitigate this risk, animals, plants, and multicellular fungi independently evolved elaborate clotting and plugging mechanisms. In the septate filamentous fungi, membrane-bound organelles plug septal pores in wounded hyphae. By contrast, vegetative hyphae in the early-diverging Mucoromycota are largely aseptate, and how their hyphae respond to wounding is unknown. Here, we show that wounding in the Mucorales leads to explosive protoplasmic discharge that is rapidly terminated by protoplasmic gelation. We identify Mucoromycota-specific Gellin proteins, whose loss of function leads to uncontrolled wound-induced protoplasmic bleeding. Gellins contain ten related ß-trefoil Gll domains, each of which possesses unique features that impart distinct gelation-related properties: some readily unfold and form high-order sheet-like structures when subjected to mechanical force from flow, while others possess hydrophobic motifs that enable membrane binding. In cell-free reconstitution, sheet-like structures formed by a partial Gellin incorporate membranous organelles. Together, these data define a mechanistic basis for regulated protoplasmic gelation, and provide new design principles for the development of artificial flow-responsive biomaterials.

Inhibition of Distinct Proline- or N-Acetylglucosamine-Induced Hyphal Formation Pathways by Proline Analogs in Candida albicans.

Candida albicans undergoes a yeast-to-hyphal transition that has been recognized as a virulence property as well as a turning point leading to biofilm formation associated with candidiasis. It is known that yeast-to-hyphal transition is induced under complex environmental conditions including temperature (above 35°C), pH (greater than 6.5), CO2, N-acetylglucosamine (GlcNAc), amino acids, RPMI-1640 synthetic culture medium, and blood serum. To identify the hyphal induction factor in the RPMI-1640 medium, we examined each component of RPMI-1640 and established a simple hyphal induction condition, that is, incubation in L-proline solution at 37°C. Incubation in GlcNAc solution alone, which is not contained in RPMI-1640, without any other materials was also identified as another simple hyphal induction condition. To inhibit hyphal formation, proline and GlcNAc analogs were examined. Among the proline analogs used, L-azetidine-2-carboxylic acid (AZC) inhibited hyphal induction under both induction conditions, but L-4-thiazolidinecarboxylic acid (T4C) specifically inhibited proline-induced hyphal formation only, while α-N-methyl-L-proline (mPro) selectively inhibited GlcNAc-induced hyphal formation. Hyphal formation in fetal bovine serum was also inhibited by AZC or T4C together with mPro without affecting the proliferation of yeast form. These results indicate that these proline analogs are ideal inhibitors of yeast-to-hyphal transition in C. albicans.

Coregulation of dimorphism and symbiosis by cyclic AMP signaling in the lichenized fungus Umbilicaria muhlenbergii.

Umbilicaria muhlenbergii is the only known dimorphic lichenized fungus that grows in the hyphal form in lichen thalli but as yeast cells in axenic cultures. However, the regulation of yeast-to-hypha transition and its relationship to the establishment of symbiosis are not clear. In this study, we show that nutrient limitation and hyperosmotic stress trigger the dimorphic change in U. muhlenbergii Contact with algal cells of its photobiont Trebouxia jamesii induced pseudohyphal growth. Treatments with the cAMP diphosphoesterase inhibitor IBMX (3-isobutyl-1-methylxanthine) induced pseudohyphal/hyphal growth and resulted in the differentiation of heavily melanized, lichen cortex-like structures in culture, indicating the role of cAMP signaling in regulating dimorphism. To confirm this observation, we identified and characterized two Gα subunits UmGPA2 and UmGPA3 Whereas deletion of UmGPA2 had only a minor effect on pseudohyphal growth, the ΔUmgpa3 mutant was defective in yeast-to-pseudohypha transition induced by hyperosmotic stress or T. jamesii cells. IBMX treatment suppressed the defect of ΔUmgpa3 in pseudohyphal growth. Transformants expressing the UmGPA3G45V or UmGPA3Q208L dominant active allele were enhanced in the yeast-to-pseudohypha transition and developed pseudohyphae under conditions noninducible to the wild type. Interestingly, T. jamesii cells in close contact with pseudohyphae of UmGPA3G45V and UmGPA3Q208L transformants often collapsed and died after coincubation for over 72 h, indicating that improperly regulated pseudohyphal growth due to dominant active mutations may disrupt the initial establishment of symbiotic interaction between the photobiont and mycobiont. Taken together, these results show that the cAMP-PKA pathway plays a critical role in regulating dimorphism and symbiosis in U. muhlenbergii.

Hülle Cells of Aspergillus nidulans with Nuclear Storage and Developmental Backup Functions Are Reminiscent of Multipotent Stem Cells.

Some aspergilli are among the most cosmopolitan and ecologically dominant fungal species. One pillar of their success is their complex life cycle, which creates specialized cell types for versatile dispersal and regenesis. One of these cell types is unique to aspergilli-the Hülle cells. Despite being known for over a century, the biological and ecological roles of Hülle cells remain largely speculative. Previously reported data on in vivo Hülle cell formation and localization have been conflicting. Our quantification reveals that Hülle cells can occur at all locations on hyphae and that they show cellular activity similar to that seen with adjacent hyphae, indicating that they develop as intricate parts of hyphal tissue. In addition, we show that during sexual development associated with two parental strains, the typically multinucleate Hülle cells can inherit nuclei from both parents, indicating that they may serve as genetic backups. We provide an easy, reproducible method to study Hülle cell biology and germination with which we investigate the 90-year-old puzzle of whether and how Hülle cells germinate. We present clear evidence for the germination of Hülle cells, and we show that Hülle cells grow hyphae that develop into a spore-producing colony. Finally, we show that Hülle cell-derived colonies produce conidiospores faster than spore-derived colonies, providing evidence for an as-yet-undescribed developmental shortcut program in Aspergillus nidulans We propose that Hülle cells represent a unique cell type as specialized hypha-derived sexual tissue with a nucleus storage function and may act as fungal backup stem cells under highly destructive conditions.IMPORTANCE The in vivo identification of Hülle cells in cases of aspergillosis infections in animals and humans illustrates their biological relevance and suggests that they might be involved in pathogenicity. It is striking that aspergilli have developed and maintained a multinucleate nurse cell that is presumably energy-intensive to produce and is usually found only in higher eukaryotes. Our findings shed light on how the understudied Hülle cells might contribute to the success of aspergilli by acting not only as nurse cells under detrimental conditions (sexual development) but also as fungal backup stem cells with the capacity to produce genetically diverse spores in an accelerated manner, thereby substantially contributing to survival in response to predator attack or under otherwise severely destructive conditions. Our study solved the 90-year-old puzzle of Hülle cell germination and provides easy, reproducible methods that will facilitate future studies on biological and ecological roles of Hülle cells in aspergilli.

Spitzenkörper assembly mechanisms reveal conserved features of fungal and metazoan polarity scaffolds.

The Spitzenkörper (SPK) constitutes a collection of secretory vesicles and polarity-related proteins intimately associated with polarized growth of fungal hyphae. Many SPK-localized proteins are known, but their assembly and dynamics remain poorly understood. Here, we identify protein-protein interaction cascades leading to assembly of two SPK scaffolds and recruitment of diverse effectors in Neurospora crassa. Both scaffolds are transported to the SPK by the myosin V motor (MYO-5), with the coiled-coil protein SPZ-1 acting as cargo adaptor. Neither scaffold appears to be required for accumulation of SPK secretory vesicles. One scaffold consists of Leashin-2 (LAH-2), which is required for SPK localization of the signalling kinase COT-1 and the glycolysis enzyme GPI-1. The other scaffold comprises a complex of Janus-1 (JNS-1) and the polarisome protein SPA-2. Via its Spa homology domain (SHD), SPA-2 recruits a calponin domain-containing F-actin effector (CCP-1). The SHD NMR structure reveals a conserved surface groove required for effector binding. Similarities between SPA-2/JNS-1 and the metazoan GIT/PIX complex identify foundational features of the cell polarity apparatus that predate the fungal-metazoan divergence.

A Whole-Plant Culture Method to Study Structural and Functional Traits of Extraradical Mycelium.

An in vivo whole-plant bi-dimensional experimental system has been devised and tested with different host plants, in order to obtain extraradical mycelium (ERM) produced by different arbuscular mycorrhizal fungi (AMF). In this system, a host plant germling is inoculated with AMF to establish mycorrhizal symbiosis, and, after colonization, newly formed extraradical hyphae and spores are removed. Then the mycorrhizal root system is wrapped in a nylon net and placed between membranes in a Petri dish, allowing ERM to grow on the membrane surface. Such extraradical hyphae may be used for in situ morphometric analyses or collected for molecular or biochemical assays: in the latter case, the plant with its root sandwich may be reassembled to renew mycelium production. In this experimental system, which was tested with diverse host plant species and lines, values of explored membrane surface areas and densities of ERM showed wide ranges of variation, and its length ranged from 9.7 ± 2.0 to 48.8 ± 9.9 m per plant, depending on host and AMF identity. Across the different plant-AMF combinations tested, the whole-plant system produced 2.0 ± 0.6 to 5.3 ± 0.3 mg of ERM fresh biomass per plant per harvest. This experimental system can be used for a wide range of AMF and host plants species, either establishing arbuscular mycorrhizas or other mycorrhizal interactions. ERM produced and collected in the whole-plant system is suitable for morphological, physiological, and molecular analyses, facilitating studies on the different aspects of mycorrhizal symbiotic interactions.

From colony to rodlet: "A six meter long portrait of the xerophilic fungus Aspergillus restrictus decorates the hall of the Westerdijk institute."

The extreme xerophilic fungus Aspergillus restrictus is used as a model for a large artwork created out of five microscopic pictures in total measuring 80 cm by 624 cm. The artwork is printed on aluminium and located at the entrance of the Westerdijk Institute, Utrecht, The Netherlands. The first picture is made from a colony of the fungus, which has a dimension of 1 cm and the last picture shows details of ornamentation on conidia and phialides of the fungus. The first two pictures of the artwork are made using a unique method of light microscopy in which many hundreds of pictures are made at different focal depths resulting in high detail and resolution of the pictures. For three other pictures, cryo-electron scanning microscopy was used including both a conventional system for lower magnification and a field emission scanning electron microscope for high resolution micrographs. The range of magnification is, at real size, between 78 and 63,000 times. When the observer passes the artwork it acts like a virtual microscope, just by walking past it you zoom-in to the smallest possible details. This coherent increase of magnification of one fungus, with very high quality light- and electron microscopy micrographs, shows different layers of fungal organization and emergent properties. These include the occurrence of secondary outcrops of hyphae and conidiophores in a colony; the formation of a stipe on a thin aerial hyphae; the presence and formation of characteristic structures on stipes, vesicles and phialides and a continuous zone between the forming conidia and phialides.

A mechanistic explanation of the transition to simple multicellularity in fungi.

Development of multicellularity was one of the major transitions in evolution and occurred independently multiple times in algae, plants, animals, and fungi. However recent comparative genome analyses suggest that fungi followed a different route to other eukaryotic lineages. To understand the driving forces behind the transition from unicellular fungi to hyphal forms of growth, we develop a comparative model of osmotrophic resource acquisition. This predicts that whenever the local resource is immobile, hard-to-digest, and nutrient poor, hyphal osmotrophs outcompete motile or autolytic unicellular osmotrophs. This hyphal advantage arises because transporting nutrients via a contiguous cytoplasm enables continued exploitation of remaining resources after local depletion of essential nutrients, and more efficient use of costly exoenzymes. The model provides a mechanistic explanation for the origins of multicellular hyphal organisms, and explains why fungi, rather than unicellular bacteria, evolved to dominate decay of recalcitrant, nutrient poor substrates such as leaf litter or wood.

Deletion of MHY1 abolishes hyphae formation in Yarrowia lipolytica without negative effects on stress tolerance.

There is a need for development of sustainable production processes for production of fats/oils and lipid derived chemicals. The dimorphic oleaginous yeast Yarrowia lipolytica is a promising organism for conversion of biomass hydrolysate to lipids, but in many such processes hyphae formation will be problematic. We have therefore constructed and compared the performance of strains carrying deletions in several published gene targets suggested to abolish hyphae formation (MHY1, HOY1 and CLA4). The MHY1-deletion was the only of the tested strains which did not exhibit hyphae formation under any of the conditions tested. The MHY1-deletion also had a weak positive effect on lipid accumulation without affecting the total fatty acid composition, irrespective of the nitrogen source used. MHY1 has been suggested to constitute a functional homolog of the stress responsive transcription factors MSN2/4 in Saccharomyces cerevisiae, the deletion of which are highly stress sensitive. However, the deletion of MHY1 displayed only minor difference on survival of a range of acute or long term stress and starvation conditions. We conclude that the deletion of MHY1 in Y.lipolytica is a reliable way of abolishing hyphae formation with few detectable negative side effects regarding growth, stress tolerance and lipid accumulation and composition.

Phylogeny and taxonomy of Ceriporia and other related taxa and description of three new species.

Species of Ceriporia (Irpicaceae, Basidiomycota) are saprotrophs or endophytes in forest ecosystems. To evaluate the taxonomy and generic relationships of Ceriporia and other related taxa, we used morphology and multigene phylogenetic analyses based on sequence data from nuc rDNA internal transcribed spacer ITS1-5.8S-ITS2 (ITS) region, nuc 28S rDNA (28S), and RNA polymerase II largest subunit (rpb1). Our results show that Ceriporia sensu lato is polyphyletic and distributed across multiple clades in the Irpicaceae, Phanerochaetaceae, and Meruliaceae. Some species previously considered in Ceriporia are now recovered in Meruliopsis, resulting in four new combinations: M. albomellea, M. crassitunicata, M. nanlingensis, and M. pseudocystidiata. Two new species of Meruliopsis are described: M. leptocystidiata from northeast China and South Korea and M. parvispora from Taiwan. Ceriporia arbuscula is described as a new species from Taiwan. Ceriporia mellita and Meruliopsis nanlingensis are newly recorded from Japan and Taiwan, and M. taxicola is recorded from Taiwan for the first time.

Pathways That Synthesize Phosphatidylethanolamine Impact Candida albicans Hyphal Length and Cell Wall Composition through Transcriptional and Posttranscriptional Mechanisms.

Candida albicans is a leading cause of systemic bloodstream infections, and synthesis of the phospholipid phosphatidylethanolamine (PE) is required for virulence. The psd1Δ/Δ psd2Δ/Δ mutant, which cannot synthesize PE by the cytidine diphosphate diacylglycerol (CDP-DAG) pathway, is avirulent in the mouse model of systemic candidiasis. Similarly, an ept1Δ/Δ mutant, which cannot produce PE by the Kennedy pathway, exhibits decreased kidney fungal burden in systemically infected mice. Conversely, overexpression of EPT1 results in a hypervirulent phenotype in this model. Thus, mutations that increase PE synthesis increase virulence, and mutations that decrease PE synthesis decrease virulence. However, the mechanism by which virulence is regulated by PE synthesis is only partially understood. RNA sequencing was performed on strains with deficient or excessive PE biosynthesis to elucidate the mechanism. Decreased PE synthesis from loss of EPT1 or PSD1 and PSD2 leads to downregulation of genes that impact mitochondrial function. Losses of PSD1 and PSD2, but not EPT1, cause significant increases in transcription of glycosylation genes, which may reflect the substantial cell wall defects in the psd1Δ/Δ psd2Δ/Δ mutant. These accumulated defects could contribute to the decreased virulence observed for mutants with deficient PE synthesis. In contrast to mutants with decreased PE synthesis, there were no transcriptional differences between the EPT1 overexpression strain and the wild type, indicating that the hypervirulent phenotype is a consequence of posttranscriptional changes. It was found that overexpression of EPT1 causes increased chitin content and increased hyphal length. These phenotypes may help to explain the previously observed hypervirulence in the EPT1 overexpressor.

Septoglomus mexicanum, a new species of arbuscular mycorrhizal fungi from semiarid regions in Mexico.

Septoglomus mexicanum is here described as a new species of arbuscular mycorrhizal fungi (AMF; Glomeromycota) based on morphological and phylogenetic analyses. It was isolated from rhizospheric soil of two endemic Mexican legumes: Prosopis laevigata and Mimosa luisana, which grow in semiarid regions of central Mexico. Septoglomus mexicanum is characterized by forming globose spores of (154.5-)202.8(-228.9) µm diam and a spore wall consisting of four layers (SWL1-SWL4): outer wall layer (SWL1) hyaline, evanescent, (1.7-)3.2(-4.3) µm thick; SWL2 laminate and smooth, orange to reddish orange, (3.1-)4.5(-6.1) µm thick; SWL3 laminate, smooth, reddish orange to reddish brown, (4.1-)5.1(-5.7) µm thick; and SWL4 hyaline, semiflexible, (0.93-)1.2(-1.4) µm thick. None of the spore wall layers stain with Melzer's reagent. The subtending hypha has a color from yellowish to golden and presents a septum on spore base. Septoglomus mexicanum can be distinguished from all other Septoglomus species by spore size and color, by spore wall structure (four layers), and by color change of the subtending hypha. Phylogenetic analysis based on the AMF extended DNA barcode covering a 1.5-kb fragment of the small subunit (SSU), internal transcribed spacer region (ITS1-5.8S-ITS2), and the large subunit (LSU) of rRNA genes places S. mexicanum in the genus Septoglomus, separated from other described Septoglomus species, especially S. turnauae, with whom it could be confused morphologically. All available sequences in public databases suggest that this new fungal species has not yet been previously detected. Thus, there are currently 149 Glomeromycota species registered in Mexico, representing 47.4% of the known species worldwide.

Magnaporthiopsis cynodontis, a novel turfgrass pathogen with widespread distribution in the United States.

The genus Magnaporthiopsis of Magnaporthaceae (Magnaporthales, Sordariomycetes, Ascomycota) contains species that are predominantly necrotrophic pathogens, often producing simple hyphopodia and dark, ectotrophic runner hyphae on plant roots and stems during colonization. Fungal isolates from turfgrass roots with dark and ectotrophic runner hyphae were examined and identified based on morphological, biological, and phylogenetic analyses. Maximum likelihood and Bayesian methods were implemented to obtain phylogenetic trees for partial sequences of the 18S nuc rDNA, ITS1-5.8S-ITS2 nuc rDNA internal transcribed spacer, and 28S nuc rDNA regions, and of the minichromosome maintenance complex 7 (MCM7), largest subunit of RNA polymerase II (RPB1), and translation elongation factor 1-alpha (TEF1) genes. Our isolates consistently formed a distinct and highly supported clade within Magnaporthiopsis. These findings were reinforced by common and distinctive biological and morphological characters. Additionally, we conducted pathogenicity evaluations and demonstrated the ability of this fungus to colonize roots of ultradwarf bermudagrass, one of its native hosts, via ectotrophic, dark runner hyphae, causing disease symptoms including root discoloration and reduced root and shoot mass. Altogether, our discoveries enabled recognition and description of a new species, Magnaporthiopsis cynodontis, which has widespread distribution in the United States.

Tradeoffs in hyphal traits determine mycelium architecture in saprobic fungi.

The fungal mycelium represents the essence of the fungal lifestyle, and understanding how a mycelium is constructed is of fundamental importance in fungal biology and ecology. Previous studies have examined initial developmental patterns or focused on a few strains, often mutants of model species, and frequently grown under non-harmonized growth conditions; these factors currently collectively hamper systematic insights into rules of mycelium architecture. To address this, we here use a broader suite of fungi (31 species including members of the Ascomycota, Basidiomycota and Mucoromycota), all isolated from the same soil, and tested for ten architectural traits under standardized laboratory conditions. We find great variability in traits among the saprobic fungal species, and detect several clear tradeoffs in mycelial architecture, for example between internodal length and hyphal diameter. Within the constraints so identified, we document otherwise great versatility in mycelium architecture in this set of fungi, and there was no evidence of trait 'syndromes' as might be expected. Our results point to an important dimension of fungal properties with likely consequences for coexistence within local communities, as well as for functional complementarity (e.g. decomposition, soil aggregation).