Akkermansia muciniphila - friend or foe in colorectal cancer?

Akkermansia muciniphila is a gram-negative anaerobic bacterium, which represents a part of the commensal human microbiota. Decline in the abundance of A. muciniphila among other microbial species in the gut correlates with severe systemic diseases such as diabetes, obesity, intestinal inflammation and colorectal cancer. Due to its mucin-reducing and immunomodulatory properties, the use of probiotics containing Akkermansia sp. appears as a promising approach to the treatment of metabolic and inflammatory diseases. In particular, a number of studies have focused on the role of A. muciniphila in colorectal cancer. Of note, the results of these studies in mice are contradictory: some reported a protective role of A. muciniphila in colorectal cancer, while others demonstrated that administration of A. muciniphila could aggravate the course of the disease resulting in increased tumor burden. More recent studies suggested the immunomodulatory effect of certain unique surface antigens of A. muciniphila on the intestinal immune system. In this Perspective, we attempt to explain how A. muciniphila contributes to protection against colorectal cancer in some models, while being pathogenic in others. We argue that differences in the experimental protocols of administration of A. muciniphila, as well as viability of bacteria, may significantly affect the results. In addition, we hypothesize that antigens presented by pasteurized bacteria or live A. muciniphila may exert distinct effects on the barrier functions of the gut. Finally, A. muciniphila may reduce the mucin barrier and exerts combined effects with other bacterial species in either promoting or inhibiting cancer development.

Fontisphaera persica gen. nov., sp. nov., a thermophilic hydrolytic bacterium from a hot spring of Baikal lake region, and proposal of Fontisphaeraceae fam. nov., and Limisphaeraceae fam. nov. within the Limisphaerales ord. nov. (Verrucomicrobiota).

A novel facultatively anaerobic moderately thermophilic bacterium, strain B-154 T, was isolated from a terrestrial hot spring in the Baikal lake region (Russian Federation). Gram-negative, motile, spherical cells were present singly, in pairs, or aggregates, and reproduced by binary fission. The strain grew at 30-57 °C and within a pH range of 5.1-8.4 with the optimum at 50 °C and pH 6.8-7.1. Strain B-154 T was a chemoorganoheterotroph, growing on mono-, di- and polysaccharides (xylan, starch, galactan, galactomannan, glucomannan, xyloglucan, pullulan, arabinan, lichenan, beta-glucan, pachyman, locust bean gum, xanthan gum). It did not require sodium chloride or yeast extract for growth. Major cellular fatty acids were anteiso-C15:0, iso-C16:0 and iso-C14:0. The respiratory quinone was MK-7. The complete genome of strain B-154 T was 4.73 Mbp in size; its G + C content was 61%. According to the phylogenomic analysis strain B-154 T forms a separate family-level phylogenetic lineage. Moreover, together with Limisphaera ngatamarikiensis and "Pedosphaera parvula" this strain forms a separate order-level phylogenetic lineage within Verrucomicrobiae class. Hence, we propose a novel order, Limisphaerales ord. nov., with two families Limisphaeraceae fam. nov. and Fontisphaeraceae fam. nov., and a novel genus and species Fontisphaera persica gen. nov., sp. nov. with type strain B-154 T. Ecogenomic analysis showed that representatives of the Limisphaerales are widespread in various environments. Although some of them were detected in hot springs the majority of Limisphaerales (54% of the studied metagenome-assembled genomes) were found in marine habitats. This study allowed a better understanding of physiology and ecology of Verrucomicrobiota - a rather understudied bacterial phylum.

Draft Genome Sequence of Thermomicrobium sp. Strain 4228-Ro, a Thermophilic Bacterium Isolated from a Kamchatka Hot Spring.

The genome of Thermomicrobium sp. strain 4228-Ro, an aerobic thermophilic bacterium isolated from a Kamchatka hot spring, was sequenced and analyzed. The genome assembly comprises 13 contigs with a total length of 3,068,448 bp. Genome analysis revealed the pathway of aerobic utilization of sugars, which was corroborated by growth experiments.

Fontivita pretiosa gen. nov., sp. nov., a thermophilic planctomycete of the order Tepidisphaerales from a hot spring of Baikal lake region.

A novel facultatively anaerobic moderately thermophilic bacterium, strain B-254T, was isolated from a terrestrial hot spring near the town of Goryachinsk in the Baikal lake region (Russian Federation). Motile spherical cells of the strain were present as single cocci, in pairs, or aggregates. The cells had a Gram negative cell wall and reproduced by binary fission. The isolate grew at 30-57 °C (opt. 50-54 °C) and at pH 5.1-8.4 (opt. 6.6-7.1). Strain B-254T was a chemoorganoheterotroph, growing on mono-, di- and polysaccharides (xylan, starch, galactan, galactomannan, xyloglucan, arabinan, curdlan, beta-glucan, locust bean gum, xanthan gum). Sodium chloride or yeast extract were not required for growth. Major cellular fatty acids were iso-C16:0, anteiso-C17:0, and C20:0; major polar lipid was phosphatidylethanolamine. The complete genome of strain B-254T was 5.54 Mb; its GC content was 64 %. According to the results of 16S rRNA gene sequence-based phylogenetic analysis and the conserved proteins sequences-based phylogenomic analysis strain B-254T was on a separate lineage within the order Tepidisphaerales (Phycisphaerae, Planctomycetes). Based on phylogenetic and phylogenomic analyses of Phycisphaerae, whole genome comparisons of Tepidisphaerales as well as distinctive phenotypic features of the strain, it was assigned to a novel genus and species for which the name Fontivita pretiosa gen. nov. sp. nov. is proposed. Strain B-254T = KCTC 82380T = VKM B-3507T.

Thermogemmata fonticola gen. nov., sp. nov., the first thermophilic planctomycete of the order Gemmatales from a Kamchatka hot spring.

A novel aerobic moderately thermophilic bacterium, designated strain 2918T, was isolated from a terrestrial hot spring of Kamchatka, Russian Federation. Gram-negative, motile, spherical cells were present singly, in pairs, or aggregates, and reproduced by budding. The strain grew at 25-60°C and within a pH range of 5.0-8.0 with an optimum at 54-60°C and pH 7.5. Strain 2918T did not require sodium chloride or yeast extract for growth. It was a chemoorganoheterotroph, growing on mono-, di- and polysaccharides (starch, lichenan, galactan, arabinan, xanthan gum, beta-glucan). No growth was observed under anaerobic conditions neither in the presence of sulfur, nitrate, or thiosulfate nor without adding any electron acceptor. Major cellular fatty acids were C18:0 and C20:0. The respiratory quinone was MK-6. The size of the genome of strain 2918T was 4.81 Mb. Genomic DNA G+C content was 60.4mol%. According to the 16S rRNA gene sequence and conserved protein sequences phylogenies, strain 2918T represented a distinct lineage of the order Gemmatales within Planctomycetes. Based on phylogenetic analysis and phenotypic features, the novel isolate was assigned to a novel genus in the Gemmatales for which the name Thermogemmata gen. nov. is proposed. Strain 2918T (=KCTC 72012T =VKM B-3161T) represents its first species Thermogemmata fonticola sp. nov.

Tenuifilum thalassicum gen. nov., sp. nov., a novel moderate thermophilic anaerobic bacterium from a Kunashir Island shallow hot spring representing a new family Tenuifilaceae fam. nov. in the class Bacteroidia.

A novel anaerobic moderately thermophilic bacterium, designated strain 38H-strT, was isolated from a 12m deep hot spring of the Kunashir Island shore. Gram-negative cells were non-spore-forming, motile, straight or curved filamentous rods, occasionally forming loops and knots. The strain grew at 20-65°C and pH range of 4.0-9.0 with an optimum at 50°C and pH 6.5-7.0. Strain 38H-strT required 0.5-2.5% NaCl (1.5% is an optimum) for growth. It was a chemoorganoheterotroph, growing on carbohydrates (starch, pullulan, alginate, laminarin, beta-glucan) or peptide mixtures and proteins (peptone, tryptone, gelatin, and α- or ß- keratins). Major products of glucose fermentation were acetate, hydrogen, and carbon dioxide. Major cellular fatty acids were iso- and anteiso-C15:0. Phosphatidylethanolamine, an unidentified phospholipid, and three unidentified polar lipids were detected in cellular lipids fractions. The quinone was MK-7. The size of complete genome of strain 38H-strT was 3.2 Mb; DNA G+C content was 38.3mol%. According to 16S rRNA gene sequence and conserved protein sequences phylogenies, strain 38H-strT represented a deeply branched lineage near the root of the class Bacteroidia. Based on phylogenetic analysis and phenotypic features the novel isolate was assigned to a novel family within the order Bacteroidales for which the name Tenuifilaceae fam. nov. is proposed. Strain 38H-strT (=DSM 100343T =VKM B-2964T) represents the first genus and species Tenuifilum thalassicum gen. nov., sp. nov.

Novel Hyperthermophilic Crenarchaeon Thermofilum adornatum sp. nov. Uses GH1, GH3, and Two Novel Glycosidases for Cellulose Hydrolysis.

A novel hyperthermophilic, anaerobic filamentous archaeon, Thermofilum adornatum strain 1910bT, is capable of growing with cellulose as its sole carbon and energy source. This strain was isolated from a terrestrial hot spring in Kamchatka, Russia. The isolate 1910bT grew optimally at a temperature of 80°C and a pH of 5.5-6.0, producing cell-bound inducible cellulases. During genome analysis, genes, encoding various glycosidases (GHs) involved in oligo- and polysaccharide hydrolysis and genes for the fermentation of sugars were identified. No homologs of currently known cellulase families were found among the GHs encoded by the 1910bT genome, suggesting that novel proteins are involved. To figure this out, a proteomic analysis of cells grown on cellulose or pyruvate (as a control) was performed. Both in-depth genomic and proteomic analyses revealed four proteins (Cel25, Cel30, Cel40, and Cel45) that were the most likely to be involved in the cellulose hydrolysis in this archaeon. Two of these proteins (Cel30 and Cel45) were hypothetical according to genome analysis, while the other two (Cel25 and Cel40) have GH3 and GH1 domains, respectively. The respective genes were heterologously expressed in Escherichia coli BL21 (DE3), and enzymatic activities of recombinant proteins were measured with carboxymethyl cellulose (CMC), Avicel and cellobiose as substrates. It was revealed that the Cel30 and Cel25 proteins were likely exoglucanases with side beta-glucosidase and endoglucanase activities, that Cel40 was a multifunctional glucanase capable of hydrolyzing beta-1,4-glucosides of various lengths, and that Cel45 was an endoglucanase with side exoglucanase activity. Taking into account that the cellulolytic activity of T. adornatum 1910bT surface protein fractions was inducible, that recombinant Cel25 and Cel30 were much less active than Cel40 and Cel45, and that their gene expressions were (almost) non-induced by CMC, we suggest that Cel40 and Cel45 play a major role in the degradation of cellulose, while Cel25 and Cel30 act only as accessory enzymes.

Thermosipho spp. Immune System Differences Affect Variation in Genome Size and Geographical Distributions.

Thermosipho species inhabit thermal environments such as marine hydrothermal vents, petroleum reservoirs, and terrestrial hot springs. A 16S rRNA phylogeny of available Thermosipho spp. sequences suggested habitat specialists adapted to living in hydrothermal vents only, and habitat generalists inhabiting oil reservoirs, hydrothermal vents, and hotsprings. Comparative genomics of 15 Thermosipho genomes separated them into three distinct species with different habitat distributions: The widely distributed T. africanus and the more specialized, T. melanesiensis and T. affectus. Moreover, the species can be differentiated on the basis of genome size (GS), genome content, and immune system composition. For instance, the T. africanus genomes are largest and contained the most carbohydrate metabolism genes, which could explain why these isolates were obtained from ecologically more divergent habitats. Nonetheless, all the Thermosipho genomes, like other Thermotogae genomes, show evidence of genome streamlining. GS differences between the species could further be correlated to differences in defense capacities against foreign DNA, which influence recombination via HGT. The smallest genomes are found in T. affectus that contain both CRISPR-cas Type I and III systems, but no RM system genes. We suggest that this has caused these genomes to be almost devoid of mobile elements, contrasting the two other species genomes that contain a higher abundance of mobile elements combined with different immune system configurations. Taken together, the comparative genomic analyses of Thermosipho spp. revealed genetic variation allowing habitat differentiation within the genus as well as differentiation with respect to invading mobile DNA.

Sporosalibacterium tautonense sp. nov., a thermotolerant, halophilic, hydrolytic bacterium isolated from a gold mine, and emended description of the genus Sporosalibacterium.

A novel strictly anaerobic, thermotolerant, moderately halophilic, organotrophic bacterium, strain MRo-4T, was isolated from a sample of a microbial mat, developed under the flow of subsurface water in TauTona gold mine, South Africa. Cells of the novel isolate stained Gram-positive and were motile, spore-forming rods, 0.2-0.3 µm in width and 5-20 µm in length. Strain MRo-4T grew at 25-50 °C, at pH 7.0-8.8 and at an NaCl concentration of 5-100 g l-1. The isolate was able to ferment yeast extract, peptone and mono-, oligo- and polysaccharides, including cellulose and chitin. Elemental sulfur, thiosulfate, sulfate, sulfite, nitrate, nitrite, fumarate and arsenate were not reduced. The major fatty acids were iso-C15 : 0, iso-C15 : 0 dimethyl acetyl and anteiso-C15 : 0. The G+C content of the DNA was 32.9 mol%. Phylogenetic analysis of 16S rRNA gene sequences of strain MRo-4T and its nearest relatives showed its affiliation to the genus Sporosalibacterium. Sporosalibacteriumfaouarense SOL3f37T, the only valid published representative of the genus, appeared to be its closest relative (96.8 % 16S rRNA gene sequence similarity). However, strains MRo-4T and S. faouarense SOL3f37T differed in temperature, pH and salinity ranges for growth, requirement for yeast extract and substrate profiles. Based on the phylogenetic analysis and physiological properties of the novel isolate, we propose a novel species, Sporosalibacterium tautonense sp. nov. The type strain is MRo-4T (=DSM 28179T=VKM B-2948T).

Tepidibacillus infernus sp. nov., a moderately thermophilic, selenate- and arsenate-respiring hydrolytic bacterium isolated from a gold mine, and emended description of the genus Tepidibacillus.

A novel aerotolerant anaerobic, moderately thermophilic, organotrophic bacterium, strain MBL-TLPT, was isolated from a sample of microbial mat, developed under the flow of subsurface water in TauTona gold mine, South Africa. Cells of the new isolate were flagellated, spore-forming rods, 0.25-0.5 µm in width and 3-15 µm in length. Strain MBL-TLPT grew in the temperature range from 25 to 58 °C, pH range from 5.6 to 8.8 and at NaCl concentration from 0 to 85 g l-1. The isolate was able to ferment yeast extract and mono-, oligo- and polysaccharides, including starch and xanthan gum. The G+C content of the DNA was 35 mol%. Phylogenetic analysis of 16S rRNA gene sequences of strain MBL-TLPT and relatives showed its affiliation to the genus Tepidibacillus. Tepidibacillus fermentans STGHT was its closest relative (97.1 % identity of 16S rRNA gene sequences). Based on phylogenetic analysis and the physiological properties of the novel isolate, we propose a novel species, Tepidibacillus infernus sp. nov., with MBL-TLPT(=DSM 28123T=VKM В-2949T) as the type strain.

Stable and Variable Parts of Microbial Community in Siberian Deep Subsurface Thermal Aquifer System Revealed in a Long-Term Monitoring Study.

The goal of this work was to study the diversity of microorganisms inhabiting a deep subsurface aquifer system in order to understand their functional roles and interspecies relations formed in the course of buried organic matter degradation. A microbial community of a deep subsurface thermal aquifer in the Tomsk Region, Western Siberia was monitored over the course of 5 years via a 2.7 km deep borehole 3P, drilled down to a Palaeozoic basement. The borehole water discharges with a temperature of ca. 50°C. Its chemical composition varies, but it steadily contains acetate, propionate, and traces of hydrocarbons and gives rise to microbial mats along the surface flow. Community analysis by PCR-DGGE 16S rRNA genes profiling, repeatedly performed within 5 years, revealed several dominating phylotypes consistently found in the borehole water, and highly variable diversity of prokaryotes, brought to the surface with the borehole outflow. The major planktonic components of the microbial community were Desulfovirgula thermocuniculi and Methanothermobacter spp. The composition of the minor part of the community was unstable, and molecular analysis did not reveal any regularity in its variations, except some predominance of uncultured Firmicutes. Batch cultures with complex organic substrates inoculated with water samples were set in order to enrich prokaryotes from the variable part of the community. PCR-DGGE analysis of these enrichments yielded uncultured Firmicutes, Chloroflexi, and Ignavibacteriae. A continuous-flow microaerophilic enrichment culture with a water sample amended with acetate contained Hydrogenophilus thermoluteolus, which was previously detected in the microbial mat developing at the outflow of the borehole. Cultivation results allowed us to assume that variable components of the 3P well community are hydrolytic organotrophs, degrading buried biopolymers, while the constant planktonic components of the community degrade dissolved fermentation products to methane and CO2, possibly via interspecies hydrogen transfer. Occasional washout of minor community components capable of oxygen respiration leads to the development of microbial mats at the outflow of the borehole where residual dissolved fermentation products are aerobically oxidized. Long-term community analysis with the combination of molecular and cultivation techniques allowed us to characterize stable and variable parts of the community and propose their environmental roles.

Complete genome sequence of and proposal of Thermofilum uzonense sp. nov. a novel hyperthermophilic crenarchaeon and emended description of the genus Thermofilum.

A strain of a hyperthermophilic filamentous archaeon was isolated from a sample of Kamchatka hot spring sediment. Isolate 1807-2 grew optimally at 85 °C, pH 6.0-6.5, the parameters being close to those at the sampling site. 16S rRNA gene sequence analysis placed the novel isolate in the crenarchaeal genus Thermofilum; Thermofilum pendens was its closest valid relative (95.7 % of sequence identity). Strain 1807-2 grew organothrophically using polysaccharides (starch and glucomannan), yeast extract or peptone as substrates. The addition of other crenarchaea culture broth filtrates was obligatory required for growth and could not be replaced by the addition of these organisms' cell wall fractions, as it was described for T. pendens. The genome of strain 1807-2 was sequenced using Illumina and PGM technologies. The average nucleotide identities between genome of strain 1807-2 and T. pendens strain HRK 5(T) and "T. adornatus" strain 1910b were 85 and 82 %, respectively. On the basis of 16S rRNA gene sequence phylogeny, ANI calculations and phenotypic differences we propose a novel species Thermofilum uzonense with the type strain 1807-2(T) (= DSM 28062(T) = JCM 19810(T)). Project information and genome sequence was deposited in Genbank under IDs PRJNA262459 and CP009961, respectively.

Thermosipho activus sp. nov., a thermophilic, anaerobic, hydrolytic bacterium isolated from a deep-sea sample.

A novel obligately anaerobic, extremely thermophilic, organotrophic bacterium, strain Rift-s3(T), was isolated from a deep-sea sample containing Riftia pachyptila sheath from Guaymas Basin, Gulf of California. Cells of the novel isolate were rods, 0.3-0.8 µm in width and 1.5-10 µm in length, surrounded by a sheath-like structure (toga). Strain Rift-s3(T) grew at temperatures ranging from 44 to 75 °C, at pH 5.5 to 8.0, and with NaCl concentrations of 3 to 60 g l(-1). Under optimum conditions (65 °C, pH 6.0, NaCl 25 g l(-1)), the doubling time was 30 min. The isolate was able to ferment mono-, oligo- and polysaccharides including cellulose, chitin, xylan and pectin, and proteins including ß-keratins, casein and gelatin. Acetate, hydrogen and carbon dioxide were the main products of glucose fermentation. The G+C content of the DNA was 30 mol%. Phylogenetic analysis of 16S rRNA gene sequences showed the affiliation of strain Rift-s3(T) with the genus Thermosipho, with Thermosipho atlanticus Ob7(T) as the closest relative (96.5 % 16S rRNA gene sequence similarity). Based on the phylogenetic analysis and physiological properties of the novel isolate we propose a novel species of the genus Thermosipho, Thermosipho activus sp. nov., with Rift-s3(T) ( = DSM 26467(T) = VKM B-2803(T)) as the type strain.

Genomic analysis of Melioribacter roseus, facultatively anaerobic organotrophic bacterium representing a novel deep lineage within Bacteriodetes/Chlorobi group.

Melioribacter roseus is a moderately thermophilic facultatively anaerobic organotrophic bacterium representing a novel deep branch within Bacteriodetes/Chlorobi group. To better understand the metabolic capabilities and possible ecological functions of M. roseus and get insights into the evolutionary history of this bacterial lineage, we sequenced the genome of the type strain P3M-2(T). A total of 2838 open reading frames was predicted from its 3.30 Mb genome. The whole proteome analysis supported phylum-level classification of M. roseus since most of the predicted proteins had closest matches in Bacteriodetes, Proteobacteria, Chlorobi, Firmicutes and deeply-branching bacterium Caldithrix abyssi, rather than in one particular phylum. Consistent with the ability of the bacterium to grow on complex carbohydrates, the genome analysis revealed more than one hundred glycoside hydrolases, glycoside transferases, polysaccharide lyases and carbohydrate esterases. The reconstructed central metabolism revealed pathways enabling the fermentation of complex organic substrates, as well as their complete oxidation through aerobic and anaerobic respiration. Genes encoding the photosynthetic and nitrogen-fixation machinery of green sulfur bacteria, as well as key enzymes of autotrophic carbon fixation pathways, were not identified. The M. roseus genome supports its affiliation to a novel phylum Ignavibateriae, representing the first step on the evolutionary pathway from heterotrophic ancestors of Bacteriodetes/Chlorobi group towards anaerobic photoautotrophic Chlorobi.

Characterization of Melioribacter roseus gen. nov., sp. nov., a novel facultatively anaerobic thermophilic cellulolytic bacterium from the class Ignavibacteria, and a proposal of a novel bacterial phylum Ignavibacteriae.

A novel moderately thermophilic, facultatively anaerobic chemoorganotrophic bacterium strain P3M-2(T) was isolated from a microbial mat developing on the wooden surface of a chute under the flow of hot water (46°C) coming out of a 2775-m-deep oil exploration well (Tomsk region, Russia). Strain P3M-2(T) is a moderate thermophile and facultative anaerobe growing on mono-, di- or polysaccharides by aerobic respiration, fermentation or by reducing diverse electron acceptors [nitrite, Fe(III), As(V)]. Its closest cultivated relative (90.8% rRNA gene sequence identity) is Ignavibacterium album, the only chemoorganotrophic member of the phylum Chlorobi. New genus and species Melioribacter roseus are proposed for isolate P3M-2(T) . Together with I. album, the new organism represents the class Ignavibacteria assigned to the phylum Chlorobi. The revealed group includes a variety of uncultured environmental clones, the 16S rRNA gene sequences of some of which have been previously attributed to the candidate division ZB1. Phylogenetic analysis of M. roseus and I. album based on their 23S rRNA and RecA sequences confirmed that these two organisms could represent an even deeper, phylum-level lineage. Hence, we propose a new phylum Ignavibacteriae within the Bacteroidetes-Chlorobi group with a sole class Ignavibacteria, two families Ignavibacteriaceae and Melioribacteraceae and two species I. album and M. roseus. This proposal correlates with chemotaxonomic data and phenotypic differences of both organisms from other cultured representatives of Chlorobi. The most essential differences, supported by the analyses of complete genomes of both organisms, are motility, facultatively anaerobic and obligately organotrophic mode of life, the absence of chlorosomes and the apparent inability to grow phototrophically.

Fervidobacterium riparium sp. nov., a thermophilic anaerobic cellulolytic bacterium isolated from a hot spring.

A novel obligately anaerobic, extremely thermophilic, organotrophic bacterium, strain 1445t(T), was isolated from a hot spring on Kunashir Island (Kuril Islands, Russia). Cells were motile rods (0.4-0.5 × 1.0-3.0 µm). The temperature range for growth at pH 7.8 was 46-80 °C, with optimum growth at 65 °C. The pH range for growth at 65 °C was pH 5.7-9.0, with optimum growth at pH 7.8. Growth was not observed at or below 40 °C, at or above 84 °C, at or below pH 5.4 or at or above pH 9.5. The isolate degraded a wide range of substrates including starch, cellulose and cellulose derivatives. Elemental sulfur stimulated growth, but sodium sulfate, sulfite and thiosulfate did not. DNA G+C content was 31 mol%. Phylogenetic analysis of 16S rRNA gene sequences showed that strain 1445t(T) belonged to the genus Fervidobacterium. 16S rRNA gene sequence similarities with strains of other species of the genus Fervidobacterium were 94.9-98.3 %; the type strain of Fervidobacterium gondwanense was the closest relative of strain 1445t(T). DNA-DNA hybridization of strain 1445t(T) and F. gondwanense AB39(T) revealed a relatedness value of 20 %. Based on phylogenetic data and physiological properties of the isolate, a novel species, designated Fervidobacterium riparium sp. nov., is proposed with strain 1445t(T) ( = DSM 21630(T) = VKM B-2549(T)) as the type strain.