The evolution of morphological development is congruent with the species phylogeny in the genus Streptomyces.

As the canonical model organism to dissect bacterial morphological development, Streptomyces species has attracted much attention from the microbiological society. However, the evolution of development-related genes in Streptomyces remains elusive. Here, we evaluated the distribution of development-related genes, thus indicating that the majority of these genes were ubiquitous in Streptomyces genomes. Furthermore, the phylogenetic topologies of related strict orthologous genes were compared to the species tree of Streptomyces from both concatenation and single-gene tree analyses. Meanwhile, the reconciled gene tree and normalization based on the number of parsimony-informative sites were also employed to reduce the impact of phylogenetic conflicts, which was induced by uncertainty in single-gene tree inference based merely on the sequence and the bias in the amount of phylogenetic information caused by variable numbers of parsimony-informative sites. We found that the development-related genes had higher congruence to the species tree than other strict orthologous genes. Considering that the development-related genes could also be tracked back to the common ancestor of Streptomyces, these results suggest that morphological development follows the same pattern as species divergence.

Cellular differentiation into hyphae and spores in halophilic archaea.

Several groups of bacteria have complex life cycles involving cellular differentiation and multicellular structures. For example, actinobacteria of the genus Streptomyces form multicellular vegetative hyphae, aerial hyphae, and spores. However, similar life cycles have not yet been described for archaea. Here, we show that several haloarchaea of the family Halobacteriaceae display a life cycle resembling that of Streptomyces bacteria. Strain YIM 93972 (isolated from a salt marsh) undergoes cellular differentiation into mycelia and spores. Other closely related strains are also able to form mycelia, and comparative genomic analyses point to gene signatures (apparent gain or loss of certain genes) that are shared by members of this clade within the Halobacteriaceae. Genomic, transcriptomic and proteomic analyses of non-differentiating mutants suggest that a Cdc48-family ATPase might be involved in cellular differentiation in strain YIM 93972. Additionally, a gene encoding a putative oligopeptide transporter from YIM 93972 can restore the ability to form hyphae in a Streptomyces coelicolor mutant that carries a deletion in a homologous gene cluster (bldKA-bldKE), suggesting functional equivalence. We propose strain YIM 93972 as representative of a new species in a new genus within the family Halobacteriaceae, for which the name Actinoarchaeum halophilum gen. nov., sp. nov. is herewith proposed. Our demonstration of a complex life cycle in a group of haloarchaea adds a new dimension to our understanding of the biological diversity and environmental adaptation of archaea.

Thermophilic Dehalococcoidia with unusual traits shed light on an unexpected past.

Although the phylum Chloroflexota is ubiquitous, its biology and evolution are poorly understood due to limited cultivability. Here, we isolated two motile, thermophilic bacteria from hot spring sediments belonging to the genus Tepidiforma and class Dehalococcoidia within the phylum Chloroflexota. A combination of cryo-electron tomography, exometabolomics, and cultivation experiments using stable isotopes of carbon revealed three unusual traits: flagellar motility, a peptidoglycan-containing cell envelope, and heterotrophic activity on aromatics and plant-associated compounds. Outside of this genus, flagellar motility has not been observed in Chloroflexota, and peptidoglycan-containing cell envelopes have not been described in Dehalococcoidia. Although these traits are unusual among cultivated Chloroflexota and Dehalococcoidia, ancestral character state reconstructions showed flagellar motility and peptidoglycan-containing cell envelopes were ancestral within the Dehalococcoidia, and subsequently lost prior to a major adaptive radiation of Dehalococcoidia into marine environments. However, despite the predominantly vertical evolutionary histories of flagellar motility and peptidoglycan biosynthesis, the evolution of enzymes for degradation of aromatics and plant-associated compounds was predominantly horizontal and complex. Together, the presence of these unusual traits in Dehalococcoidia and their evolutionary histories raise new questions about the timing and selective forces driving their successful niche expansion into global oceans.

Comparative genomic analysis and proposal of Clostridium yunnanense sp. nov., Clostridium rhizosphaerae sp. nov., and Clostridium paridis sp. nov., three novel Clostridium sensu stricto endophytes with diverse capabilities of acetic acid and ethanol production.

OBJECTIVES: Genus Clostridium sensu stricto is generally regarded as the true Clostridium genus, which includes important human and animal pathogens and industrially relevant microorganisms. Besides, it is also a prominent member of plant-associated endophytes. However, our knowledge of endophytic Clostridium is limited. METHODS: In this study, the endophytes were isolated under anaerobic condition from the roots of Paris polyphylla Smith var. yunnanensis. Subsequently, a polyphasic taxonomic approach was used to clarify their taxonomic positions. The fermentation products were measured in the isolates with HPLC analysis. Comparative genomics was performed on these new strains and other relatives. RESULTS: In total, nine endophytic strains belonging to the genus Clostridium sensu stricto were isolated, and three of them were identified as new species. Seven of nine strains could produce acetate, propionate, and butyrate. Only two strains could produce ethanol, although genomics analysis suggested that only two of them were without genes for solventogenesis. Different from the endophytic strains, the phylogenetically closely related non-endophytic strains showed significant enrichment effects on some metabolic pathways involving environmental information processing, carbohydrate, and amino acid metabolisms, etc. It suggests that the genomes of these endophytic strains had undergone subtle changes associated with environmental adaptations. CONCLUSION: Consequently, strains YIM B02505T, YIM B02515T, and YIM B02565T are proposed to represent a new species of the genus Clostridium sensu stricto, for which the names Clostridium yunnanense sp. nov., Clostridium rhizosphaerae sp. nov., and Clostridium paridis sp. nov. are suggested.

Azospirillum Endophyticum sp. nov., an Endophyte of Paris Polyphylla Smith var. Yunnanensis.

A Gram-negative, facultative anaerobic bacterial strain, designated YIM B02556T, was isolated from the root of Paris polyphylla Smith var. yunnanensis collected from Yunnan Province, southwest China. By using a polyphasic approach, its taxonomic position was investigated. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain YIM B02556T belonged to the genus Azospirillum and the 16S rRNA gene sequence similarity values of strain YIM B02556T to the type strains of members of this genus ranged from 94.9 to 98.3%. Overall genome relatedness index (OGRI) analysis estimated based on average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) between YIM B02556T and other Azospirillum species type strains were <90.8% and <37.8%, lower than the limit of species circumscription. Cells of the strain were characterized as oxidase- and catalase-positive, with motility provided by flagella. The growth conditions of the strain were found to occur at 20-40 °C (optimum, 35 °C), and pH 6.0-9.5 (optimum, pH 7.5). Strain YIM B02556T can tolerate 2% NaCl concentration. Strain YIM B02556T contained Q-10 as the major ubiquinone. The major fatty acids were C18:1 ω7c and summed feature three (C16:1 ω7c and/or C16:1 ω6c). The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, and phosphatidylethanolamine. Based on polyphasic analysis, strain YIM B02556T could be differentiated genotypically and phenotypically from recognized species of the genus Azospirillum. Therefore, the isolate represents a novel species, for which the name Azospirillum endophyticum is proposed. The type strain is YIM B02556T (=JCM 34631T=CGMCC 1.18654T).

Genome-based analyses reveal heterotypic synonyms of Streptomyces species and associated subspecies.

In the genus Streptomyces, several validly described species have been reduced to synonyms of earlier described species though additional synonyms remain to be detected given the previous dependence on traditional phenotypic methods. In this study, genome-based procedures, including DNA-DNA hybridization analyses, overall genome-related indices, such as ANI, dDDH and AAI, revealed that certain strains recorded genomic indices above the threshold values used to define species boundaries. The results of phylogenetic and phylogenomic trees based on concatenated and phylogenomic analyses showed that 33 out of 364 tested species could be assigned to 15 species groups and that 18 Streptomyces species names be reclassified as later heterotypic synonyms of earlier validly published species. Consequently, it is proposed that S. albaduncus is a later heterotypic synonym of S. griseoloalbus; S. bellus is a synonym of S. coeruleorubidus; S. gancidicus and S. rubiginosus are synonyms of S. pseudogriseolus; S. niveoruber is a synonym of S. griseoviridis; S. griseomycini is a synonym of S. griseostramineus; S. jietaisiensis is a synonym of S. griseoaurantiacus; S. pluricolorescens is a synonym of S. rubiginosohelvolus; S. nashvillensis is a synonym of S. tanashiensis; S. yerevanensis is a synonym of S. flaveus; S. durhamensis is a synonym of S. filipinensis; S. recifensis is a synonym of S. griseoluteus; S. canaries and S. olivaceoviridis are synonyms of S. corchorusii; S. melanosporofaciens is a synonym of S. antimycoticus; S. albulus is a synonym of S. noursei; and S. janthinus and S. violarus are synonyms of S. violaceus. Additionally, seven of these 18 Streptomyces species have been designated subspecies.

Neobacillus paridis sp. nov., an endophyte of Paris polyphylla Smith var. yunnanensis.

A novel endophytic strain, designated YIM B02564T, was isolated from the root of Paris polyphylla Smith var. yunnanensis obtained from Yunnan Province, southwest China. By using a polyphasic approach, cells of the strain were characterized as facultative anaerobic, Gram-positive and rod-shaped. The growth conditions of the strain were found to occur at 20-55 °C (optimum, 30 °C), pH 6.0-9.0 (optimum, pH 7.0). Strain YIM B02564T can tolerate 2% NaCl concentration. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain YIM B02564T belonged to the genus Neobacillus and the 16S rRNA gene sequence similarity values of strain YIM B02564T to the type strains of members of this genus ranged from 95.6 to 97.8%. The DNA G+C content of strain YIM B02564T calculated from the whole genome sequence was 41.6 mol%. Values of the ANI and the dDDH between strain YIM B02564T and its closely related Neobacillus species were below 77.9% and 21.5%. Strain YIM B02564T contained MK-7 as the major menaquinone, iso-C15:0 and anteiso-C15:0 as the major fatty acids. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, an unidentified aminophospholipid and four unidentified lipids. It contained meso-diaminopimelic acid in the cell-wall peptidoglycan. On the basis of polyphasic analysis, strain YIM B02564T could be differentiated genotypically and phenotypically from recognized species of the genus Neobacillus. The isolate therefore represents a novel species, for which the name Neobacillus paridis is proposed. The type strain is YIM B02564T (= JCM 34668T = CGMCC 1.18655T).

Janibacter endophyticus sp. nov., an Endophytic Actinobacterium Isolated from the Root of Paris polyphylla Smith var. Yunnanensis.

A novel endophytic actinobacterium, designated as strain YIM B02568T, was isolated from the root of Paris polyphylla Smith var. Yunnanensis obtained from Yunnan Province, southwest China. Strain YIM B02568T was characterized using a polyphasic approach. Phylogenetic analysis indicated that this isolate belonged to the genus Janibacter. The 16S rRNA gene sequence similarity values of strain YIM B02568T to the type strains of members of this genus ranged from 95.8 to 98.6%. However, overall genome relatedness indices were significantly lower than the widely accepted species-defined threshold. The cell wall of strain YIM B02568T contained meso-diaminopimelic acid. The major menaquinone was MK-8(H4). The main polar lipids were phosphatidylglycerol, diphosphatidylglycerol, and phosphatidylinositol. The major cellular fatty acids were comprised of iso-C16:0 and C18:1 ω9c. The DNA G + C content was 71.6 mol%. Based on the data from the polyphasic studies, we propose that strain YIM B02568T represents a novel species within the genus Janibacter, Janibacter endophyticus sp. nov. The type strain is YIM B02568T (= JCM 34639T = CGMCC 1.18658T).

Chryseobacterium paridis sp. nov., an endophytic bacterial species isolated from the root of Paris polyphylla Smith var. yunnanensis.

A Gram-negative, yellow-pigmented, rod-shaped bacterial strain YIM B02567T was isolated from the root of Paris polyphylla Smith var. yunnanensis in China. Strain YIM B02567T grew optimally at 25-30 °C and at pH 7.0 in the absence of NaCl on nutrient agar. Phylogenetic analyses based on 16S rRNA gene sequences revealed that strain YIM B02567T belong to the genus Chryseobacterium, and was closely related to Chryseobacterium piperi CTMT and Chryseobacterium soli DSM 19298T. Whole genome sequencing indicated that the genome size was 4,774,612 bp and with a G + C content of 34.5 mol%. Values of the ANI and the dDDH between strain YIM B02567T and its closely related Chryseobacterium species were below 81.72% and 24.7%. Strain YIM B02567T contained menaquinone-6 as the sole isoprenoid quinone, anteiso-C15:0, iso-C17:1 ω9c and iso-C17:0 3-OH as major fatty acids and phosphatidylethanolamine as major polar lipid. Based on the polyphasic analyses, strain YIM B02567T could be differentiated genotypically and phenotypically from recognized species of the genus Chryseobacterium. The isolate, therefore, represents a novel species, for which the name Chryseobacterium paridis sp. nov. is proposed. The type strain is YIM B02567T (= CGMCC 1.18657T).

Vallicoccus soli gen. nov., sp. nov., a novel actinobacterium isolated from soil, and description of Vallicoccaceae fam. nov., Motilibacterales ord. nov.

A novel Gram-stain-positive, aerobic, cocci-shaped actinobacterium, designated YIM 75000T, was isolated from a soil sample collected from a dry-hot river valley in Yunnan Province, P.R. China. Growth was observed at 10-45 °C (optimal 37 °C), 0-8% (w/v) NaCl (optimal at 0-3% NaCl) and pH 6.0-8.0 (optimal at pH 7.3). The peptidoglycan contained LL-diaminopimelic acid, glycine, glutamic acid as well as alanine and its type was A3γ with an LL-Dpm-Gly interpeptide bridge. The major cellular fatty acids (> 10%) were C16:0, Summed In Feature 3 (C16:1 ω6c/C16:1 ω7c) and C17:1 ω8c. The predominant menaquinone was MK-9(H4). The major whole-cell sugars contained rhamnose, ribose, arabinose and mannose. The DNA G+C content was 77.0 mol%. The 16S rRNA gene sequence similarities of strain YIM 75000T with other species were less than 94%. Phylogenetic analyses based on 16S rRNA gene sequences and genome data, revealed that strain YIM 75000T together with the genus Motilibacter formed a distinct phylogenetic lineage within the phylum Actinobacteria, separating them from members of all orders. Strain YIM 75000T showed 73.4-73.7% average nucleotide identity and 19.5-19.7% digital DNA-DNA hybridization identity with the closely related genus Motilibacter. Based on the phenotypic, phylogenetic and chemotaxonomic data, it is proposed that the new isolate represents the nomenclature type of the novel species Vallicoccus soli gen. nov., sp. nov. (YIM 75000T = DSM 45377T = KCTC 49228T = CGMCC 1.13844T) which is the nomenclature type of the novel genus Vallicoccus gen. nov. within Vallicoccaceae fam. nov and Motilibacterales ord. nov in the phylum Actinobacteria. The family Vallicoccaceae fam. nov. and the order Motilibacterales (contains Vallicoccaceae fam. nov. and Motilibacteraceae Lee 2013) ord. nov. are formally proposed.

Plasmids Related to the Symbiotic Nitrogen Fixation Are Not Only Cooperated Functionally but Also May Have Evolved over a Time Span in Family Rhizobiaceae.

Rhizobia are soil bacteria capable of forming symbiotic nitrogen-fixing nodules associated with leguminous plants. In fast-growing legume-nodulating rhizobia, such as the species in the family Rhizobiaceae, the symbiotic plasmid is the main genetic basis for nitrogen-fixing symbiosis, and is susceptible to horizontal gene transfer. To further understand the symbioses evolution in Rhizobiaceae, we analyzed the pan-genome of this family based on 92 genomes of type/reference strains and reconstructed its phylogeny using a phylogenomics approach. Intriguingly, although the genetic expansion that occurred in chromosomal regions was the main reason for the high proportion of low-frequency flexible gene families in the pan-genome, gene gain events associated with accessory plasmids introduced more genes into the genomes of nitrogen-fixing species. For symbiotic plasmids, although horizontal gene transfer frequently occurred, transfer may be impeded by, such as, the host's physical isolation and soil conditions, even among phylogenetically close species. During coevolution with leguminous hosts, the plasmid system, including accessory and symbiotic plasmids, may have evolved over a time span, and provided rhizobial species with the ability to adapt to various environmental conditions and helped them achieve nitrogen fixation. These findings provide new insights into the phylogeny of Rhizobiaceae and advance our understanding of the evolution of symbiotic nitrogen fixation.

Reclassification of Friedmanniella endophytica, Lysinimicrobium sediminis and Lechevalieria rhizosphaerae as Microlunatus kandeliicorticis nom. nov., Demequina sediminis comb. nov. and Lentzea rhizosphaerae comb. nov., respectively.

According to Rule 37a of the International Code of Nomenclature of Prokaryotes, the name of a taxon must be changed if the nomenclatural type of the taxon is excluded. Recently, in a transfer of actinobacterial species, three species - Friedmanniella endophytica Tuo et al. 2016, Lysinimicrobium sediminis Hamada et al. 2017 and Lechevalieria rhizosphaerae Zhao et al. 2017 - were not transferred with their type species. Therefore, to resolve these nomenclatural issues, Microlunatus kandeliicorticis nom. nov., Demequina sediminis comb. nov. and Lentzea rhizosphaerae comb. nov. are proposed, respectively.

A recently evolved diflavin-containing monomeric nitrate reductase is responsible for highly efficient bacterial nitrate assimilation.

Nitrate is one of the major inorganic nitrogen sources for microbes. Many bacterial and archaeal lineages have the capacity to express assimilatory nitrate reductase (NAS), which catalyzes the rate-limiting reduction of nitrate to nitrite. Although a nitrate assimilatory pathway in mycobacteria has been proposed and validated physiologically and genetically, the putative NAS enzyme has yet to be identified. Here, we report the characterization of a novel NAS encoded by Mycolicibacterium smegmatis Msmeg_4206, designated NasN, which differs from the canonical NASs in its structure, electron transfer mechanism, enzymatic properties, and phylogenetic distribution. Using sequence analysis and biochemical characterization, we found that NasN is an NADPH-dependent, diflavin-containing monomeric enzyme composed of a canonical molybdopterin cofactor-binding catalytic domain and an FMN-FAD/NAD-binding, electron-receiving/transferring domain, making it unique among all previously reported hetero-oligomeric NASs. Genetic studies revealed that NasN is essential for aerobic M. smegmatis growth on nitrate as the sole nitrogen source and that the global transcriptional regulator GlnR regulates nasN expression. Moreover, unlike the NADH-dependent heterodimeric NAS enzyme, NasN efficiently supports bacterial growth under nitrate-limiting conditions, likely due to its significantly greater catalytic activity and oxygen tolerance. Results from a phylogenetic analysis suggested that the nasN gene is more recently evolved than those encoding other NASs and that its distribution is limited mainly to Actinobacteria and Proteobacteria. We observed that among mycobacterial species, most fast-growing environmental mycobacteria carry nasN, but that it is largely lacking in slow-growing pathogenic mycobacteria because of multiple independent genomic deletion events along their evolution.

Paenibacillus paridis sp. nov., an endophytic bacterial species isolated from the root of Paris polyphylla Smith var. yunnanensis.

A Gram-reaction-positive, endospore-forming and rod-shaped bacterial strain, designated py1325T, was isolated from the root of Paris polyphylla Smith var. yunnanensis collected from Yunnan Province, PR China, and subjected to a polyphasic taxonomic characterization. It grew optimally with 0-1 % NaCl (w/v), at pH 7 and at 30 °C. The major respiratory quinone was MK-7 and the diagnostic diamino acid in the cell-wall peptidoglycan was meso-diaminopimelic acid. The major cellular fatty acid was anteiso-C15 : 0. The polar lipids consisted of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, two unidentified aminophospholipids, two unidentified phospholipids and two unidentified lipids. The results of 16S rRNA gene sequence analysis revealed the highest levels of sequence similarity with respect to Paenibacillus luteus R-3T (99.0 %), Paenibacillus sinopodophylli CCTCC AB 2016047T (97.9 %), Paenibacillus castaneae DSM 19417T (97.5 %) and Paenibacillus endophyticus LMG 27297T (97.2 %). The digital DNA-DNA hybridization and average nucleotide identity values between py1325T and these species ranged 20.6-53.3 % and 79.9-93.6 %. The G+C content of the genomic DNA was 47.7 mol%. According to the phylogenetic, phenotypic and chemotaxonomic evidence, strain py1325T clearly represents a novel species of the genus Paenibacillus, for which the name Paenibacillus paridis sp. nov. is proposed. The type strain is py1325T (=CCTCC AB 2015220T=LMG 29068T).

Elioraea thermophila sp. nov., a thermophilic bacterium from hot spring of the class Alphaproteobacteria, emended description of the genus Elioraea and proposal of Elioraeaceae fam. nov.

A Gram-staining-negative, aerobic, curved rod-shaped and thermophilic bacterial strain, designated YIM 72297T, was isolated from a sediment sample collected from a hot spring in Tengchong county, Yunnan province, south-west China. Growth was observed at pH 5.0-9.0 with an optimum of pH 7.0-7.5, and at 45-60 °C with an optimum of 55 °C. Positive for catalase and oxidase. The 16S rRNA gene sequence comparison indicated that strain YIM 72297T was most closely related to Elioraea tepidiphila DSM 17972T (96.9 %) and showed <91 % sequence similarities to members of the order Rhodospirillales. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain YIM 72297T formed a distinct lineage within the genus Elioraea, and revealed that the genus Elioraea formed a novel family-level clade in the order Rhodospirillales. The ANI and the dDNA-DNA hybridization estimate values between strains YIM 72297T and Elioraea tepidiphila DSM 17972T were 70.8 and 20.1 %, respectively. Strain YIM 72297T contained Q-10 as the predominant ubiquinone. The major fatty acids (>5 %) were summed C18 : 0 (35.8 %), summed feature 8 (30.1 %), C16 : 0 (12.6 %), C18 : 1 2OH (5.6 %) and C16 : 0 2OH (5.4 %). The polar lipids consisted of phosphatidylcholine, phosphatidylethanolamine, diphosphosphatidylglycerol and phosphatidylglycerol in addition to two unidentified aminolipids. The DNA G+C content of YIM 72297T was 70.8 mol% (draft genome). On the basis of the polyphasic taxonomic evidence presented in this study, strain YIM 72297T should be classified as representing a novel species of the genus Elioraea, for which the name Elioraea thermophila sp. nov. is proposed, with the type strain YIM 72297T (=CCTCC AB 2017169T=KCTC 62323T). In addition, a novel family, Elioraeaceae fam. nov., is proposed to accommodate the genus Elioraea.

Bailinhaonella thermotolerans gen. nov., sp. nov., a new member of the order Streptosporangiales.

A Gram-positive, aerobic, non-motile actinobacterium, designated YIM 75507T, that was isolated from a soil sample collected from a dry-hot valley, was subjected to a polyphasic taxonomic study. The isolate formed branched hyphae and no fragmentation was found. Clustered spore chains were borne from aerial mycelium. The cell-wall peptidoglycan contained glutamic acid, alanine and meso-diaminopimelic acid. Whole-cell sugars were galactose, mannose, glucosamine, glucose and ribose. The major menaquinones were MK-9(H6), MK-9(H8) and MK-10(H6). The polar phospholipids contained phosphatidylmethylethanolamine, phosphatidylethanolamine and ninhydrin-positive phosphoglycolipid. Major fatty acids were iso-C16 : 0 and 10-methyl-C17 : 0. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain YIM 75507T formed a stable and distinct lineage clustered with the genus Sinosporangium in the family Streptosporangiaceae. The draft genome sequence of strain YIM 75507T exhibited low average nucleotide identity to the closest related strain, Sinosporangium album CPCC 201354T (83.97 %), well below the 95-96 % species circumscription threshold. The G+C content of the genomic DNA was 73.8 mol%. On the basis of morphological, chemotaxonomic and phylogenetic evidence, strain YIM 75507T is assigned to a novel species of a new genus, for which the name Bailinhaonella thermotolerans gen. nov., sp. nov. is proposed. The type strain of Bailinhaonella thermotolerans is YIM 75507T (=KCTC 49229T=CGMCC 4.7547T).

Genome-based taxonomic classification within the family Thermoactinomycetaceae.

The family Thermoactinomycetaceaecomprises 43 validly published species, which were identified by a polyphasic taxonomic study based on molecular phylogenetics, physiological and biochemical characteristics. However, phylogenetic analysis merely based on 16S rRNA gene sequences cannot infer a robust and reliable phylogeny. For disentangling the phylogenetic relationships among members of this family, we used a large collection of genome data and the approach of phylogenomics, to re-examine their taxonomy. The topologies of phylogenomic trees are different from those of the 16S rRNA gene sequences. In addition, based on the average nucleotide identity, digital DNA-DNA hybridization, phenotypic and biochemical characteristics, we found that Laceyella sediminis should be reclassified as a later heterotypic synonym of Laceyella tengchongensis; and reclassified Thermoactinomyces guangxiensis as Paenactinomyces guangxiensis gen. nov., comb. nov.; and establish Novibacillaceae fam. nov. to accommodate the genus Novibacillus as the type genus. In addition, compared to values calculated directly from genome sequences, the genomic DNA G+C contents mentioned in some species descriptions are too imprecise; and the corrected G+C content values have a significantly better fit to the phylogeny. Thus, the corresponding emendations of species descriptions are also proposed. In this paper, phylogenomics has been used to resolve the classification of the family Thermoactinomycetaceae.

Rhodobacter thermarum sp. nov., a novel phototrophic bacterium isolated from sediment of a hot spring.

An ovoid to rod-shaped, phototrophic, purple non-sulfur bacterium was isolated from a sediment sample of a hot spring in Tibet, China. Cells of strain YIM 73036T were Gram-stain negative, non-motile and multiplied by binary fission. Strain YIM 73036T grew optimally at pH 7.0-7.5 at 37-45 °C. Growth occurred in 0.5-3.5% (w/v) NaCl. Vitamins were not required for growth. The presence of photosynthesis genes pufL and pufM were shown and photosynthesis pigments were formed. Bacteriochlorophyll α, the bacteriopheophytin and carotenoids were present as photosynthetic pigments. Internal cytoplasmic membranes were of the lamellar type. The organism YIM 73036T was able to grow chemo-organoheterophically, chemo-lithoautotrophically and photo-organoheterotrophically but photo-lithoautotrophic and fermentative growth were not demonstrated. Phylogenetic analysis on the basis of 16S rRNA gene sequences showed that strain YIM 73036T is closely related to Rhodobacter blasticus ATCC 33485T (96.65% sequence similarity) and clustered with species of the genus Rhodobacter of the family Rhodobacteraceae. Whole-genome sequence analyses based on the average nucleotide BLAST identity (ANI < 82%) indicated that this isolate belongs to a novel species. The genomic DNA G+C content of organism YIM 73036T was determined to be 66.0 mol%. Strain YIM 73036T contained Q-10 as the predominant ubiquinone and C18:1ω7c, C18:1ω7c 11-methyl and C18:0 as the major fatty acids. The major polar lipids were phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine and unidentified phospholipid. Differential phenotypic and chemotaxonomic properties, together with the phylogenetic distinctiveness, demonstrated that strain YIM 73036T is distinguishable from other species of the genus Rhodobacter. On the basis of the data presented, strain YIM 73036T is considered to represent a novel species of the genus Rhodobacter, for which the name Rhodobacter thermarum sp. nov. [type strain YIM 73036T (= KCTC 52712T = CCTCC AB 2016298T)] is proposed.

Aquabacterium tepidiphilum sp. nov., a moderately thermophilic bacterium isolated from a hot spring.

A Gram-stain-negative, aerobic, non-spore-forming and rod-shaped bacterium, designated YIM 730274T, was isolated from a sediment sample collected from a hot spring located in Tibet, PR China, and was characterized by using a polyphasic taxonomy approach. Cells were motile by means of a polar flagellum. The strain was oxidase- and catalase-positive, and contained polyalkanoates and polyphosphate as storage polymers. Growth occurred at 25-50 °C, at pH 6.0-8.5 and with 0.5-1.0 % NaCl. The major fatty acids (>10 %) were summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c), summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and C16 : 0. The known polar lipids comprised of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylserine. The isoprenoid quinone was Q-8. The G+C content of genomic DNA was 70.7 mol%. The results of phylogenetic analyses based on 16S rRNA gene sequences indicated that the strain forms a monophyletic branch at the periphery of the evolutionary radiation occupied by the genus Aquabacterium in the class Betaproteobacteria. The most closely related phylogenetic neighbours were Aquabacterium limnoticumABP-4T (97.8 % 16S rRNA gene sequence identity) and Aquabacterium communeB8T (97.2 % 16SrRNA gene sequence identity). DNA-DNA relatedness values between YIM 730274T and A. limnoticum KCTC 23306T (46.4±0.4 %) and A. commune DSM 11901T (42.2±1.2 %) were well below the 70 % limit for species identification. YIM 730274T was distinguishable from other members of the genus Aquabacterium by the differences in phenotypic, chemotaxonomic and genotypic characteristics. YIM 730274T merits recognition as a representative of a novel species of the genus Aquabacterium. It is proposed that the isolate should be classified in the genus Aquabacterium as representing a novel species, Aquabacteriumtepidiphilum sp. nov. The type strain is YIM 730274T (=KCTC 52716T=CCTCC AB 2016295T).