Sphingosinicella terrae sp. nov. Isolated from a Desert Soil and Reclassification of Sphingomonas deserti as Sphingosinicella deserti comb. nov.

A motile, rod-shaped and yellow-coloured bacterium, designated strain SYSU D60001T, was isolated from a desert soil sample. Cells were Gram-stain-negative, catalase-negative and oxidase-positive. The major cellular fatty acids were summed feature 8 (C18:1 ω7c and/or C18:1 ω6c) and C16:0. The respiratory quinone was ubiquinone-10. The genomic DNA G+C content was 68%. The polar lipids detected were diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, an unidentified phospholipid and five unidentified polar lipids. Phylogenetic analysis based on the 16S rRNA gene sequences revealed that strain SYSU D60001T represents a novel species of the genus Sphingosinicella, with closely related strains Sphingosinicella ginsenosidimutans BS1T (95.81%), Sphingomonas deserti GL-C-18T (95.75%) and Sphingosinicella humi QZX222T (95.18%). Data from polyphasic taxonomy study suggest that the isolate represents a novel species in the genus Sphingosinicella, for which the name Sphingosinicella terrae sp. nov. is proposed. The type strain of the proposed new taxon is SYSU D60001T (= DSM 104938T = KCTC 52780T = NBRC 112955T). We also propose the reclassification of Sphingomonas deserti as Sphingosinicella deserti comb. nov.

Genome-based reclassification of the genus Meiothermus along with the proposal of a new genus Allomeiothermus gen. nov.

Phylogenomic analyses were performed on the nine species of the genus Meiothermus and four species of the genus Calidithermus. Phylogenetic analysis, low values of genomic relatedness indices and functional diversity analysis indicated that Meiothermus silvanus should not be classified within the clades for Meiothermus and Calidithermus but instead be reclassified as a new genus, for which we propose the name Allomeiothermus gen. nov., with Allomeiothermus silvanus comb. nov. as type species. In addition, the species Meiothermus cateniformans Zhang et al. (Int J Syst Evol Microbial 60:840-844, 2010) should also be reclassified as a later heterotypic synonym of Meiothermus taiwanensis Chen et al. (Int J Syst Evol Microbiol 52:1647-1654, 2002) emend. Raposo et al. (2019). This reclassification is based on the high genomic relatedness indices (98.8% ANI; 90.2% dDDH; 99% AAI) that are above the threshold values necessary for defining a new species, as well as on the observation of overlapping functions on Principal Coordinate Analysis plot generated from Clusters of Orthologous Genes.

Haloterrigena gelatinilytica sp. nov., a new extremely halophilic archaeon isolated from salt-lake.

Two extremely halophilic strains, designated SYSU A558-1T and SYSU A121-1, were isolated from a saline sediment sample collected from Aiding salt-lake, China. Cells of strains SYSU A558-1T and SYSU A121-1 were Gram-stain-negative, coccoid, and non-motile. The strains were aerobic and grew at NaCl concentration of 10-30% (optimum, 20-22%), at 20-55 °C (optimum, 37-42 °C) and at pH 6.5-8.5 (optimum, 7.0-8.0). Cells lysed in distilled water. The polar lipids were phosphatidyl choline, phosphatidylglycerol phosphate methyl ester, disulfated diglycosyl diether-1 and unidentified glycolipid. Phylogenetic analysis based on the 16S rRNA gene sequence revealed that the two strains SYSU A558-1T and SYSU A121-1 were closely related to the membranes of the genus Haloterrigena. Phylogenetic and phylogenomic trees of strains SYSU A558-1T and SYSU A121-1 demonstrated a robust clade with Haloterrigena turkmenica, Haloterrigena salifodinae and Haloterrigena salina. The genomic DNA G + C content of strains SYSU A558-1T and SYSU A121-1 were 65.8 and 65.0%, respectively. Phenotypic, phylogenetic, chemotaxonomic and genome analysis suggested that the two strains SYSU A558-1T and SYSU A121-1 represent a novel species of the genus Haloterrigena, for which the name Haloterrigena gelatinilytica sp. nov. is proposed. The type strain is SYSU A558-1T (= KCTC 4259T = CGMCC 1.15953T).

Halegenticoccus tardaugens sp. nov., an extremely halophilic archaeon isolated from a saline soil.

Two extremely halophilic archaea, isolates SYSU A00711T and SYSU A00630, were isolated from a sediment soil sample collected from the Aiding lake, China. Cells of these isolates were cocci, non-motile and stained Gram-negative. They grew optimally at 37 °C, with 20-22% NaCl (w/v) and at pH 7.5-8.0. Cells lysed in distilled water. Major polar lipids were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, mannosyl glucosyl diether, sulfated mannosyl glucosyl diether, and two unidentified glycolipids. Pairwise sequence comparison revealed that isolates SYSU A00711T and SYSU A00630 were closely related to Halegenticoccus soli SYSU A9-0T (94.1 and 94.0% 16S rRNA gene sequence similarities; 94.0 and 94.2% rpoB' gene similarities, respectively). The overall genomic relatedness indices values between the two isolates and Halegenticocus soli SYSU A9-0 T were: AAI, both 79.6%; ANI, 84.6 and 84.5%; dDDH, 32.5 and 26.3%, respectively. Phylogenetic trees based on the 16S rRNA gene, rpoB' gene, and genome sequences demonstrated a robust clade of these two isolates with Halegenticoccus soli SYSU A9-0T. The DNA G + C contents of these two isolates are both 64.7% (genome method). Based on the differences in phenotypic, chemotaxonomic, and phylogenetic properties, isolates SYSU A00711T and SYSU A00630 are characterized to represent a novel species in the genus Halegenticoccus, for which the name Halegenticoccus tardaugens sp. nov. is proposed. The type strain of the species Halegenticoccus tardaugens is SYSU A00711T (= KCTC 4245T = CGMCC 1.15768T).

Insight into the function and evolution of the Wood-Ljungdahl pathway in Actinobacteria.

Carbon fixation by chemoautotrophic microbes such as homoacetogens had a major impact on the transition from the inorganic to the organic world. Recent reports have shown the presence of genes for key enzymes associated with the Wood-Ljungdahl pathway (WLP) in the phylum Actinobacteria, which adds to the diversity of potential autotrophs. Here, we compiled 42 actinobacterial metagenome-assembled genomes (MAGs) from new and existing metagenomic datasets and propose three novel classes, Ca. Aquicultoria, Ca. Geothermincolia and Ca. Humimicrobiia. Most members of these classes contain genes coding for acetogenesis through the WLP, as well as a variety of hydrogenases (NiFe groups 1a and 3b-3d; FeFe group C; NiFe group 4-related hydrogenases). We show that the three classes acquired the hydrogenases independently, yet the carbon monoxide dehydrogenase/acetyl-CoA synthase complex (CODH/ACS) was apparently present in their last common ancestor and was inherited vertically. Furthermore, the Actinobacteria likely donated genes for CODH/ACS to multiple lineages within Nitrospirae, Deltaproteobacteria (Desulfobacterota), and Thermodesulfobacteria through multiple horizontal gene transfer events. Finally, we show the apparent growth of Ca. Geothermincolia and H2-dependent acetate production in hot spring enrichment cultures with or without the methanogenesis inhibitor 2-bromoethanesulfonate, which is consistent with the proposed homoacetogenic metabolism.

Diversity and Distribution of Anaerobic Ammonium Oxidation Bacteria in Hot Springs of Conghua, China.

Anaerobic ammonium oxidation (anammox) is an important process of the nitrogen cycle, and the anammox bacteria have been studied in a wide variety of environments. However, the distribution, diversity, and abundance of anammox bacteria in hot springs remain enigmatic. In this study, the anammox process was firstly investigated in hot springs of Conghua, China. Anammox-like bacterial sequences that closely affiliated to "Candidatus Brocadia," "Candidatus Kuenenia," "Candidatus Scalindua," "Candidatus Anammoxoglobus," and "Candidatus Jettenia" were detected. Several operational taxonomic units (OTUs) from this study shared low sequence identities to the 16S rRNA gene of the known anammox bacteria, suggesting that they might be representing putative novel anammox bacteria. A quantitative PCR analysis of anammox-specific 16S rRNA gene confirmed that the abundance of anammox bacteria ranged from 1.60 × 104 to 1.20 × 107 copies L-1. Nitrate was a key environmental factor defining the geographical distribution of the anammox bacterial community in the hot spring ecosystem. Dissolved inorganic carbon had a significant influence on anammox bacterial biodiversity. Our findings for the first time revealed that the diverse anammox bacteria, including putative novel anammox bacterial candidates, were present in Conghua hot spring, which extended the existence of anammox bacteria to the hot springs in China and expands our knowledge of the biogeography of anammox bacteria. This work filled up the research lacuna of anammox bacteria in Chinese hot spring habitat and would guide for enrichment strategies of anammox bacteria of Conghua hot springs.

From ecophysiology to cultivation methodology: filling the knowledge gap between uncultured and cultured microbes.

Earth is dominated by a myriad of microbial communities, but the majority fails to grow under in situ laboratory conditions. The basic cause of unculturability is that bacteria dominantly occur as biofilms in natural environments. Earlier improvements in the culture techniques are mostly done by optimizing media components. However, with technological advancement particularly in the field of genome sequencing and cell imagining techniques, new tools have become available to understand the ecophysiology of microbial communities. Hence, it becomes easier to mimic environmental conditions in the culture plate. Other methods include co-culturing, emendation of growth factors, and cultivation after physical cell sorting. Most recently, techniques have been proposed for bacterial cultivation by employing genomic data to understand either microbial interactions (network-directed targeted bacterial isolation) or ecosystem engineering (reverse genomics). Hopefully, these techniques may be applied to almost all environmental samples, and help fill the gaps between the cultured and uncultured microbial communities.

Nesterenkonia haasae sp. nov., an alkaliphilic actinobacterium isolated from a degraded pasture in Songnen Plain.

An alkaliphilic actinobacterial strain, designated Hz 6-5T, was isolated from saline-alkaline soil from Songnen Plain in north-eastern China. The isolate formed light yellow-colored colonies and its cells were Gram-staining positive, non-motile, and non-spore-forming short rods. The strain was aerobic with optimal growth at 33 °C, pH 9.0, and in the presence of 0.5% (w/v) NaCl or 3% (w/v) KCl. It was catalase-positive and oxidase-negative. The isolate had highest 16S rRNA gene sequence similarities to the type strains of the species Nesternkonia natronophila M8T (98.2%), N. salmonea GY074T (98.1%), and N. sphaerica GY239T (97.4%), and the isolate formed a subclade with the type strains of these species in the neighbor-joining tree based on the 16S rRNA gene sequences. The phylogenetic tree based on the phylogenomic analysis also showed the same results. The DNA‒DNA relatedness (DDH) values of isolate Hz 6-5T with N. natronophila M8T, N. halophila DSM 16378T, and N. halobia CGMCC 1.2323T were 21.2%, 36.5%, and 32.0%, respectively. The characteristic diamino acid of strain Hz 6-5T was found to be lysine. The respiratory quinones were MK-9, MK-8, MK-7(H4), MK-7(H2) and MK-7 and the major cellular fatty acids (> 10%) were anteiso-C15:0, anteiso-C17:0 and iso-C16:0. The polar lipids detected for strain Hz 6-5T were diphosphatidylglycerol, phosphatidylcholine, phosphatidylglycerol, phosphatidylinositol, an unidentified glycolipid, and two unidentified phospholipids. The DNA G + C content of isolate Hz 6-5T was 60.8%. Based on the results of phylogenetic analysis supported by morphological, physiological, chemotaxonomic, and other differentiating phenotypic evidence, strain Hz 6-5T is considered to represent a novel species of the genus Nesterenkonia, for which the name Nesterenkonia haasae sp. nov. is proposed. The type strain is Hz 6-5T (=CPCC 205100T=NBRC 113521T).

Seramator thermalis gen. nov., sp. nov., a novel cellulose- and xylan-degrading member of the family Dysgonamonadaceae isolated from a hot spring.

Two anaerobic bacteria, designated strains SYSU GA16112T and SYSU GA16107, were isolated from a hot spring in Tengchong County, Yunnan Province, south-west PR China. Phylogenetic analyses based on 16S rRNA gene sequences showed that strains SYSU GA16112T and SYSU GA16107 belong to the family Dysgonamonadaceae. Cells of strains SYSU GA16112T and SYSU GA16107 were Gram-stain-negative, rod-shaped and non-motile. The major fatty acids (>10 %) of strains SYSU GA16112T and SYSU GA16107 were identified as anteiso-C15 : 0 and anteiso-C17 : 0 3OH. The polar lipid profile of strain SYSU GA16112T was found to consist of phosphatidylethanolamine, two unidentified aminophospholipids, two unidentified phosphoglycolipids, two unidentified aminolipids and one unidentified polar lipid, while that of strain SYSU GA16107 consisted of phosphatidylethanolamine, two unidentified polar lipids, three unidentified aminophospholipids, two unidentified phosphoglycolipids and one unidentified aminolipid. The genomic DNA G+C contents of strains SYSU GA16112T and SYSU GA16107 were determined to be 41.90 and 41.89 %, respectively, and the average nucleotide identity value between them was 99.99 %. Based on their morphological and physiological properties, and results of phylogenetic analyses, strains SYSU GA16112T and SYSU GA16107 are considered to represent a novel species of a novel genus, for which the name Seramator thermalis gen. nov., sp. nov. (type strain SYSU GA16112T=CGMCC 1.5281T=KCTC 15753T) is proposed.

Isolation of Clostridium from Yunnan-Tibet hot springs and description of Clostridium thermarum sp. nov. with lignocellulosic ethanol production.

Lignocellulose is considered a major source of renewable energy that serve as an alternative to the fossil fuels. Members of the genus Clostridium are some of the many microorganisms that have the ability to degrade lignocellulose efficiently to sugar, which can be further converted to biofuel. In this study, we isolated twelve Clostridium strains from hot spring samples of Yunnan and Tibet, of which isolates SYSU GA15002T and SYSU GA17076 showed low 16S rRNA gene sequence identity profiles to any of the validly named Clostridium strains (<94.0%). Studies using a polyphasic taxonomy approach concluded that the two isolates represent one novel species of the genus Clostridium, for which we propose the name Clostridium thermarum sp. nov., with SYSU GA15002T as the type strain of the species. Isolate SYSU GA15002T has an optimum growth temperature at 45°C. Fermentation of the substrates cellobiose, cellulose, xylan and untreated straw powder by this strain results in the production of ethanol, along with acetate and formate. The complete pathways for the conversion of cellulose and xylan to ethanol is also predicted from the genome of isolate SYSU GA15002T, which revealed a single step conversion of lignocellulosic biomass through consolidated bioprocessing. This paper is a comprehensive study encompassing isolation, polyphasic taxonomy, lignocellulose biodegradation and the genomic information of Clostridium in Yunnan-Tibet hot springs.

Unraveling bacteria-mediated degradation of lignin-derived aromatic compounds in a freshwater environment.

Terrestrial organic carbon-lignin plays a crucial role in the global carbon balance. However, limited studies presented the functional and ecological traits of lignin decomposers population in natural aquatic ecosystem. In this study, we performed a multi-omics analysis by deploying amplicon, metagenomic, and metatranscriptomic approaches to identify the key potential degraders and pathways involved lignin-derived aromatic compounds in the later stage of lignin degradation. By establishing microcosms with model lignin-derived aromatic compound (vanillic acid, VAN), based on the estimated absolute abundance (EAA) and the metagenome-assembled genomes (MAGs), novel potential lignin-derived aromatic compounds degraders were identified in the aquatic ecosystem. Furthermore, members of the phyla Proteobacteria and Actinobacteria were the potential major lignin-derived aromatic compounds degraders in the studied ecosystem. Our study demonstrated that genomes of the class Betaproteobacteria (Proteobacteria) possess a complete enzymatic system for the degradation of diarylpropanes, vanillate and protocatechuate, besides having the capacity to degrade other lignin-derived aromatic compounds. This study provides strong evidence for the ability of aquatic bacteria to degrade lignin-derived aromatic compounds and suggest that different microbes might occupy different niches in the later stage of lignin degradation.

Network-directed efficient isolation of previously uncultivated Chloroflexi and related bacteria in hot spring microbial mats.

The perplexity of the complex multispecies community interactions is one of the many reasons why majority of the microorganisms are still uncultivated. We analyzed the entire co-occurrence networks between the OTUs of Tibet and Yunnan hot spring samples, and found that less abundant OTUs such as genus Tepidimonas (relative abundant <1%) had high-degree centricity (key nodes), while dominant OTUs particularly genus Chloroflexus (relative abundant, 13.9%) formed the peripheral vertexes. A preliminary growth-promotion assay determined that Tepidimonas sp. strain SYSU G00190W enhanced the growth of Chloroflexus sp. SYSU G00190R. Exploiting this result, an ameliorated isolation medium containing 10% spent-culture supernatant of Tepidimonas sp. strain SYSU G00190W was prepared for targeted isolation of Chloroflexi in the Tibet and Yunnan hot spring samples. 16S rRNA gene fingerprinting characterized majority of the colonies isolated from these media as previously uncultivated Chloroflexi, of which 36 are potential novel species (16S rRNA sequence identity <98.5%). Metabolomes studies indicated that the spent-culture supernatant comprises several low-molecular-weight organic substrates that can be utilized as potential nutrients for the growth of these bacteria. These findings suggested that limited knowledge on the interaction of microbes provide threshold to traditional isolation method.

Nocardiopsis deserti sp. nov., isolated from a high altitude Atacama Desert soil.

The taxonomic status of a Nocardiopsis strain, designated H13T, isolated from a high altitude Atacama Desert soil, was established by using a polyphasic approach. The strain was found to have chemotaxonomic, cultural and morphological characteristics consistent with its classification within the genus Nocardiopsis and formed a well-supported clade in the Nocardiopsis phylogenomic tree together with the type strains of Nocardiopsis alborubida, Nocardiopsis dassonvillei and Nocardiopsis synnematoformans. Strain H13T was distinguished from its closest relatives by low average nucleotide identity (93.2-94.9 %) and in silico DNA-DNA hybridization (52.5-62.4 %) values calculated from draft genome assemblies and by a range of phenotypic properties. On the basis of these results, it is proposed that the isolate be assigned to the genus Nocardiopsis as Nocardiopsis deserti sp. nov. with isolate H13T (=CGMCC 4.7585T=KCTC 49249T) as the type strain.

Vitreimonas flagellata gen. nov., sp. nov., a novel member of the family Hyphomonadaceae isolated from an activated sludge sample.

A coccobacilli-shaped proteobacterium, designated strain SYSU XM001T, was isolated from an activated sludge sample collected from JiMei sewage treatment plant, Xiamen, PR China. Cells were Gram-stain-negative, catalase-positive and oxidase-negative. The 16S rRNA gene sequence of strain SYSU XM001T shared less than 92 % sequence identities with members of the class Alphaproteobacteria, with highest sequence similarity to Aquidulcibacter paucihalophilus TH1-2T (91.6 %; family Hyphomonadaceae, order Rhodobacterales). The strain exhibited growth at 25-37 °C, pH 7.0-9.0 and in the presence of up to 1 % (w/v) NaCl. Its chemotaxonomic features included ubiquinone-10 as the respiratory isoprenologue, iso-C16 : 0, 10-methyl C16 : 0 TSBA and anteiso-C17 : 0 as major cellular fatty acids and monoglycosyldiglyceride, glucuronopyranosyldiglyceride and two unidentified glycolipids as the main polar lipids. The DNA G+C content was determined to be 62.9 % (draft genome). Analyses of the phylogenetic data and differences in the chemotaxonomic and biochemical features from related genera in the family Hyphomonadaceae indicated that strain SYSU XM001T merits representation of a novel species of a novel genus, for which the name Vitreimonas flagellata gen. nov., sp. nov. is proposed. The type strain of Vitreimonas flagellata is SYSU XM001T (=CGMCC 1.16661T=KCTC 62915T).

Genome analysis reveals that Nocardiopsis baichengensis Li et al. 2006 is a later heterotypic synonym of Nocardiopsis halophila Al-Tai and Ruan 1994.

A genome-based phylogeny of the publicly available genomes of the genus Nocardiopsis reveals that Nocardiopsis baichengensis YIM 90130T is closely related to Nocardiopsis halophila DSM 44494T. Overall genome relatedness indices between the genomes of the two species were above the threshold values necessary for defining a new species (dDDH, 82.9 %; ANIb, 97.8 %; ANIm, 98.3 %; AAI, 97.7 %). Both species showed a similar G+C content of 73.6 mol% in their genomes. Considering the high similarity between the genomes of the two species, we propose that Nocardiopsisbaichengesis Li et al. 2006 should be reclassified as a later heterotypic synonym of Nocardiopsis halophila Al-Tai and Ruan 1994.

Update on the classification of higher ranks in the phylum Actinobacteria.

Genome analysis is one of the main criteria for description of new taxa. Availability of genome sequences for all the actinobacteria with a valid nomenclature will, however, require another decade's works of sequencing. This paper describes the rearrangement of the higher taxonomic ranks of the members of the phylum 'Actinobacteria', using the phylogeny of 16S rRNA gene sequences and supported by the phylogeny of the available genome sequences. Based on the refined phylogeny of the 16S rRNA gene sequences, we could arrange all the members of the 425 genera of the phylum 'Actinobacteria' with validly published names currently in use into six classes, 46 orders and 79 families, including 16 new orders and 10 new families. The order Micrococcales Prévot 1940 (Approved Lists 1980) emend. Nouioui et al. 2018 is now split into 11 monophyletic orders: the emended order Micrococcales and ten proposed new orders Aquipuribacterales, Beutenbergiales, Bogoriellales, Brevibacteriales, Cellulomonadales, Demequinales, Dermabacterales, Dermatophilales, Microbacteriales and Ruaniales. Further, the class 'Actinobacteria' Stackebrandt et al. 1997 emend. Nouioui et al. 2018 was described without any nomenclature type, and therefore the name 'Actinobacteria' is deemed illegitimate. In accordance to Rule 8 of the International Code of Nomenclature of Prokaryotes, Parker et al. 2019, we proposed the name Actinomycetia which is formed by using the stem of the name Actinomycetales Buchanan 1917 (Approved Lists 1980) emend. Zhi et al. 2009, to replace the name 'Actinobacteria'. The nomenclature type of the proposed new class Actinomycetia is the order Actinomycetales Buchanan 1917 (Approved Lists 1980) emend. Zhi et al. 2009.

Rhodobacter flagellatus sp. nov., a thermophilic bacterium isolated from a hot spring.

A thermophilic bacterium, designated SYSU G03088T, was isolated from Moincer hot spring, Tibet, PR China. Polyphasic taxonomic analyses and whole-genome sequencing were used to determine the taxonomic position and genomic profiles of the strain. Phylogenetic analysis using 16S rRNA gene sequence indicated that SYSU G03088T showed highest sequence similarity to Rhodobacter blasticus CGMCC 1.3365T (96.0 % sequence identity). The strain could be differentiated from most recognized species of the genus Rhodobacter by its slightly purple colony colour, distinct phenotypic characters and low ANI values. Cells were Gram-staining negative, and oval-to-rod shaped. Poly-ß-hydroxybutyrate and vesicular intracytoplasmic membrane structures were formed inside cells. Growth occurred optimally at 45 °C and pH 7.0. Ubiquinone 10 was the only respiratory quinone. The major fatty acids (>10 %) were C18 : 0, C18 : 1ω7c 11-methyl and summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c). The detected polar lipids of SYSU G03088T included diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylmethylethanolamine. The DNA G+C content of SYSU G03088T was 67.7 % (genome). On the basis of the differences in the phenotypic characteristics and phylogenetic analyses, SYSU G03088T is considered to represent a novel species of the genus Rhodobacter, for which the name Rhodobacter flagellatus sp. nov. is proposed. The type strain is SYSU G03088T (=CGMCC 1.16876T=KCTC 72354T).

A xylan-degrading thermophilic and obligate anaerobe Xylanivirga thermophila gen. nov., sp. nov., isolated from an anammox dominant wastewater treatment plant, and proposal of Xylanivirgaceae fam. nov.

In our search for novel anaerobes with potential carbohydrate polymers degrading activity, we have isolated a xylan-degrading bacterial strain SYSU GA17129T from an anammox bacteria dominant wastewater treatment plant. Phylogenetic analysis of the 16S rRNA gene sequence indicated the strain SYSU GA17129T belong to the order Clostridiales and shared highest sequence identity with Caldicoprobacter faecalis DSM 20678T (89.9%). The strain was thermophilic, obligately anaerobic, non-motile and rod shaped. Optimum growth of the strain was observed at 45 °C, pH 8.0 and in the presence of 0.5% NaCl (w/v). The chemotaxonomic features of the strain SYSU GA17129T comprised of C14:0 FAME, iso-C15:0 FAME and C16:0 FAME as the major fatty acids (>10%), diphosphatidylglycerol, phosphatidylinositol mannoside, an unidentified phospholipid, three unidentified polar lipids and two unidentified glycolipids as its polar lipids, and meso-diaminopimelic acid (meso-DAP) as the diamino acid in peptidoglycan. The G + C content of the genomic DNA was 35.9%. The strain could be distinguished from other defined families within the order Clostridiales by the differences in phenotypic and physiological characteristics, distinct phylogenetic lineage in 16S rRNA gene- and genome-based phylogenies and low genomic relatedness index. Based on these distinguishing properties, strain SYSU GA17129T is proposed to represent a new species of a new genus Xylanivirga thermophila gen. nov., sp. nov., within a new family Xylanivirgaceae fam. nov. The type species of the new taxon is SYSU GA17129T (=KCTC 15754T = CGMCC 1.5282T). This strain is characterized within the order Clostridiales, class Clostridia of the phylum Firmicutes.