Rhodoferax lithotrophicus sp. nov., a neutrophilic iron-oxidizing and -reducing bacterium isolated from iron-rich freshwater sediments.

A neutrophilic iron-oxidizing and -reducing bacterium, strain MIZ03T, was previously isolated from a wetland in Ibaraki, Japan. Here, we report the detailed characteristics of this strain. It was motile with a single polar flagellum, and Gram-stain-negative. It could grow not only chemolithoautotrophically but also chemoorganotrophically by aerobic respiration and fermentation. Major cellular fatty acids were C16 : 1 ω7c/C16 : 1 ω6c, and C16 : 0. Phylogenetic analyses indicated that strain MIZ03T belonged to the genus Rhodoferax. This strain was closely related to Rhodoferax ferrireducens with 98.5 % of 16S rRNA gene sequence similarity. Based on its phenotypic and genomic based characteristics, we conclude that strain MIZ03T represents a new species in the genus Rhodoferax. We propose the name Rhodoferax lithotrophicus sp. nov. to accommodate this strain. The type strain is MIZ03T (=JCM 34246T=DSM 113266T). We also propose the name Rhodoferax koreensis sp. nov., of which the type strain is DCY110T (=KCTC 52288T=JCM 31441T), for the effectively, but not yet validly, published name 'Rhodoferax koreense'.

Draft genome sequence of an ubiquinone-10 producing Methylobacterium durans LRY1-08 isolated from lichen in Thailand.

A ubiquitous and pink-pigmented facultatively methylotrophic bacterium, designated LRY1-08 (=JCM 33120), was isolated from a lichen in Thailand. Strain LRY1-08 and Methylobacterium durans NBRC 112876T shared 99.92 % similarity based on the 16S rRNA gene sequence. The draft genome of LRY1-08 was 5.26 Mbp with 4,952 protein-coding sequences and an average G + C content of 70.0 mol%. Comparing strain LRY1-08 to M. durans NBRC 112876T, the ANIb, ANIm, AAI, and digital DNA-DNA hybridization values were 96.29 %, 97.10 %, 96.7 %, and 82.29 %, respectively. Based on the phenotypic characteristics and genome analysis, it was identified as M. durans. Its genomic sequence data revealed the PHB and CoQ10 biosynthesis genes. Therefore, the results offer suggestions for further investigation into possible applications of this bacterium in biotechnology. The draft genome was deposited at DDBJ/EMBL/GenBank (DNA Databank of Japan/European Molecular Biology Laboratory/Genbank) (JAYEEX000000000).

Corrigendum: Iron corrosion concomitant with nitrate reduction by Iodidimonas nitroreducens sp. nov. isolated from iodide-rich brine associated with natural gas.

[This corrects the article DOI: 10.3389/fmicb.2023.1232866.].

Iron corrosion concomitant with nitrate reduction by Iodidimonas nitroreducens sp. nov. isolated from iodide-rich brine associated with natural gas.

Microbially influenced corrosion (MIC) may contribute significantly to corrosion-related failures in injection wells and iron pipes of iodine production facilities. In this study, the iron (Fe0) corroding activity of strain Q-1 isolated from iodide-rich brine in Japan and two Iodidimonas strains phylogenetically related to strain Q-1 were investigated under various culture conditions. Under aerobic conditions, the Fe0 foil in the culture of strain Q-1 was oxidized in the presence of nitrate and yeast extract, while those of two Iodidimonas strains were not. The amount of oxidized iron in this culture was six times higher than in the aseptic control. Oxidation of Fe0 in aerobic cultures of nitrate-reducing bacterium Q-1 was dependent on the formation of nitrite from nitrate. This Fe0 corrosion by nitrate-reducing bacterium Q-1 started after initial nitrite accumulation by day 4. Nitrate reduction in strain Q-1 is a unique feature that distinguishes it from two known species of Iodidimonas. Nitrite accumulation was supported by the encoding of genes for nitrate reductase and the missing of genes for nitrite reduction to ammonia or nitrogen gas in its genome sequence. Phylogenetic position of strain Q-1 based on the 16S rRNA gene sequence was with less than 96.1% sequence similarity to two known Iodidimonas species, and digital DNA-DNA hybridization (dDDH) values of 17.2-19.3%, and average nucleotide identity (ANI) values of 73.4-73.7% distinguished strain Q-1 from two known species. In addition of nitrate reduction, the ability to hydrolyze aesculin and gelatin hydrolysis and cellular fatty acid profiles also distinguished strain Q-1 from two known species. Consequently, a new species, named Iodidimonas nitroreducens sp. nov., is proposed for the nitrate-reducing bacterium strain Q-1T.

Faecalibacterium hominis Liu et al. 2023 is a later heterotypic synonym of Faecalibacterium duncaniae Sakamoto et al. 2022.

A strain of the recently validated species Faecalibacterium hominis shares 99.0 % 16S rRNA gene sequence similarity with the type strain of Faecalibacterium duncaniae. The aim of this study was to evaluate the taxonomic relationship between F. hominis and F. duncaniae. F. duncaniae JCM 31915T showed 73.0 % digital DNA-DNA hybridization (dDDH) value with F. hominis JCM 39347T. The average nucleotide identity (ANI) value between these two strains was 96.7 %. These results indicate that F. duncaniae JCM 31915T and F. hominis JCM 39347T represent members of the same species. Based on these data, we propose Faecalibacterium hominis as a later heterotypic synonym of Faecalibacterium duncaniae. An emended description is provided.

Growth of succinate consumer Dialister hominis is supported by Bacteroides thetaiotaomicron.

This study revealed an interaction between the gut commensal bacterium Bacteroides thetaiotaomicron JCM 5827T and asaccharolytic bacterium Dialister hominis JCM 33369T, which uses succinate instead of carbohydrates for growth. D. hominis usually forms extremely small colonies on Brucella blood agar plates. However, when co-cultured with B. thetaiotaomicron, D. hominis grew noticeably and formed larger colonies than those in the single culture, especially near B. thetaiotaomicron colonies. Although D. hominis barely grew in Gifu anaerobic medium broth, adding 1% succinate improved its growth. In the mixed culture, the succinate produced by B. thetaiotaomicron was mostly converted to propionate. This result was consistent with the single culture of D. hominis in the succinate-containing broth and our previous report on Phascolarctobacterium faecium, a succinate-utilizing gut bacterium. Our series of studies suggests that syntrophy within the human gut microbiota occurs via succinate.

The Genus Iodidimonas: From Its Discovery to Potential Applications.

The genus Iodidimonas was recently proposed in the class Alphaproteobacteria. Iodidimonas strains are aerobic, mesophilic, neutrophilic, moderately halophilic, and chemo-organotrophic. They were first discovered in natural gas brine water containing a very high level of iodide (I-). They exhibited a unique phenotypic feature of iodide oxidation to form molecular iodine (I2). Iodidimonas was also enriched and isolated from surface seawater supplemented with iodide, and it is clearer now that their common habitats are those enriched with iodide. In such environments, Iodidimonas species seem to attack microbial competitors with the toxic form I2 to occupy their ecological niche. The iodide-oxidizing enzyme (IOX) purified from the Iodidimonas sp. strain Q-1 exhibited high catalytic efficiency for iodide and consisted of at least two proteins IoxA and IoxC. IoxA is a putative multicopper oxidase with four conserved copper-binding regions but is phylogenetically distinct from other bacterial multicopper oxidases. The IOX/iodide system could be used as a novel enzyme-based antimicrobial system which can efficiently kill Bacillus spores. Furthermore, the IOX/iodide system can be applied to the decolorization of recalcitrant dyes, where iodide may function as a novel inorganic natural redox mediator.

Genome-based, phenotypic and chemotaxonomic classification of Faecalibacterium strains: proposal of three novel species Faecalibacterium duncaniae sp. nov., Faecalibacterium hattorii sp. nov. and Faecalibacterium gallinarum sp. nov.

Faecalibacterium prausnitzii is one of the most important butyrate-producing bacteria in the human gut. Previous studies have suggested the presence of several phylogenetic groups, with differences at the species level, in the species, and a taxonomic re-evaluation is thus essential for further understanding of ecology of the important human symbiont. Here we examine the phenotypic, physiological, chemotaxonomic and phylogenomic characteristics of six F. prausnitzii strains (BCRC 81047T=ATCC 27768T, A2-165T=JCM 31915T, APC918/95b=JCM 39207, APC942/30-2=JCM 39208, APC924/119=JCM 39209 and APC922/41-1T=JCM 39210T) deposited in public culture collections with two reference strains of Faecalibacterium butyricigenerans JCM 39212T and Faecalibacterium longum JCM 39211T. Faecalibacterium sp. JCM 17207T isolated from caecum of broiler chicken was also included. Three strains of F. prausnitzii (BCRC 81047T, JCM 39207 and JCM 39209) shared more than 96.6 % average nucleotide identity (ANI) and 69.6 % digital DNA-DNA hybridization (dDDH) values, indicating that the three strains are members of the same species. On the other hand, the remaining three strains of F. prausnitzii (JCM 31915T, JCM 39208 and JCM 39210T) were clearly separated from the above three strains based on the ANI and dDDH values. Rather, JCM 39208 showed ANI and dDDH values over the cut-off values of species discrimination (>70 % dDDH and >95-96 % ANI) with F. longum JCM 39211T, whereas JCM 31915T, JCM 39210T and JCM 17207T did not share dDDH and ANI values over the currently accepted cut-off values with any of the tested strains, including among them. Furthermore, the cellular fatty acid patterns of these strains were slightly different from other F. prausnitzii strains. Based on the collected data, F. prausnitzii JCM 31915T, F. prausnitzii JCM 39210T and Faecalibacterium sp. JCM 17207T represent three novel species of the genus Faecalibacterium, for which the names Faecalibacterium duncaniae sp. nov. (type strain JCM 31915T=DSM 17677T=A2-165T), Faecalibacterium hattorii sp. nov. (type strain JCM 39210T=DSM 107841T=APC922/41-1T) and Faecalibacterium gallinarum sp. nov. (type strain JCM 17207T=DSM 23680T=ic1379T) are proposed.

Sideroxyarcus emersonii gen. nov. sp. nov., a neutrophilic, microaerobic iron- and thiosulfate-oxidizing bacterium isolated from iron-rich wetland sediment.

A neutrophilic iron-oxidizing bacterium, strain MIZ01T, which was previously isolated from a wetland in Ibaraki, Japan, was taxonomically characterized in detail. Strain MIZ01T was a motile, curved-rod shaped, Gram-stain-negative bacterium. It was able to grow at 10-40 °C (optimally at 30-35 °C) and at pH 5.5-7.0 (optimally at pH 6.0). It grew microaerobically and chemolithoautotrophically using thiosulfate, in addition to ferrous iron, as the sole electron donor. Major cellular fatty acids of strain MIZ01T were C16 : 1 ω7c/C16 : 1 ω6c and C16 : 0. The complete genome sequence (2.74 Mbp) was determined, showing that its DNA G+C content was 60.0 mol%. Phylogenetic analyses indicated that strain MIZ01T belonged to the family Gallionellaceae, class Betaproteobacteria, and was closely related to an isolate tentatively named 'Sideroxydans lithotrophicus' ES-1 (98.2 % of 16S rRNA gene sequence similarity). Based on its phenotypic and phylogenetic characteristics, we conclude that strain MIZ01T represents a new genus and species in the family Gallionellaceae for which we propose the name Sideroxyarcus emersonii gen. nov., sp. nov. The type strain is strain MIZ01T (=JCM 39089T=DSM 111897T).

Neotabrizicola shimadae gen. nov., sp. nov., an aerobic anoxygenic phototrophic bacterium harbouring photosynthetic genes in the family Rhodobacteraceae, isolated from a terrestrial hot spring.

A bacteriochlorophyll-containing bacterium, designated as strain N10T, was isolated from a terrestrial hot spring in Nagano Prefecture, Japan. Gram-stain-negative, oxidase- and catalase-positive and ovoid to rod-shaped cells showed the features of aerobic anoxygenic phototrophic bacteria, i.e., strain N10T synthesised bacteriochlorophylls under aerobic conditions and could not grow anaerobically even under illumination. Genome analysis found genes for bacteriochlorophyll and carotenoid biosynthesis, light-harvesting complexes and type-2 photosynthetic reaction centre in the chromosome. Phylogenetic analyses based on the 16S rRNA gene sequence and 92 core proteins revealed that strain N10T was located in a distinct lineage near the type species of the genera Tabrizicola and Xinfangfangia and some species in the genus Rhodobacter (e.g., Rhodobacter blasticus). Strain N10T shared < 97.1% 16S rRNA gene sequence identity with those species in the family Rhodobacteraceae. The digital DNA-DNA hybridisation, average nucleotide identity and average amino acid identity values with the relatives, Tabrizicola aquatica RCRI19T (an aerobic anoxygenic phototrophic bacterium), Xinfangfangia soli ZQBWT and R. blasticus ATCC 33485T were 19.9-20.7%, 78.2-79.1% and 69.1-70.1%, respectively. Based on the phenotypic features, major fatty acid and polar lipid compositions, genome sequence and phylogenetic position, a novel genus and species are proposed for strain N10T, to be named Neotabrizicola shimadae (= JCM 34381T = DSM 112087T). Strain N10T which is phylogenetically located among aerobic anoxygenic phototrophic bacteria (Tabrizicola), bacteriochlorophyll-deficient bacteria (Xinfangfangia) and anaerobic anoxygenic phototrophic bacteria (Rhodobacter) has great potential to promote studies on the evolution of photosynthesis in Rhodobacteraceae.

Adlercreutzia hattorii sp. nov., an equol non-producing bacterium isolated from human faeces.

Two obligately anaerobic, Gram-stain-positive, rod-shaped bacteria were isolated from faecal samples of healthy humans in Japan. 16S rRNA gene sequence analysis indicated that these two strains (8CFCBH1T and 9CBH6) belonged to the genus Adlercreutzia, which is known as an equol-producing bacterium. The closest neighbours of strain 8CFCBH1T were Adlercreutzia equolifaciens subsp. equolifaciens DSM 19450T (98.6%), Adlercreutzia equolifaciens subsp. celatus do03T (98.4%), Adlercreutzia muris WCA-131-CoC-2T (96.6%), Parvibacter caecicola NR06T (96.4%), Adlercreutzia caecimuris B7T (95.3%) and Adlercreutzia mucosicola Mt1B8T (95.3%). The closest relatives to strain 9CBH6 were A. equolifaciens subsp. equolifaciens DSM 19450T (99.8%), A. equolifaciens subsp. celatus do03T (99.6%) and A. muris WCA-131-CoC-2T (96.8%). Strain 8CFCBH1T showed 22.3-53.5% digital DNA-DNA hybridization (dDDH) values with its related species. In addition, the average nucleotide identity (ANI) values between strain 8CFCBH1T and its related species ranged from 75.4 to 93.3%. On the other hand, strain 9CBH6 was considered as A. equolifaciens based on the dDDH and ANI values (>70% dDDH and >95-96% ANI). Strain 9CBH6 showed daidzein-converting activity, as expected from the result of genome analysis. The genome of strain 8CFCBH1T lacked four genes involved in equol production. Growing cells of strain 8CFCBH1T were not capable of converting daidzein. Based on the collected data, strain 8CFCBH1T represents a novel species in the genus Adlercreutzia, for which the name Adlercreutzia hattorii sp. nov. is proposed. The type strain of A. hattorii is 8CFCBH1T (=JCM 34083T=DSM 112284T).

Caldicellulosiruptor diazotrophicus sp. nov., a thermophilic, nitrogen-fixing fermentative bacterium isolated from a terrestrial hot spring in Japan.

A novel nitrogen-fixing fermentative bacterium, designated as YA01T, was isolated from Nakabusa hot springs in Japan. The short-rod cells of strain YA01T were Gram-positive and non-sporulating. Phylogenetic trees of the 16S rRNA gene sequence and concatenated sequences of 40 single-copy ribosomal genes revealed that strain YA01T belonged to the genus Caldicellulosiruptor and was closely related to Caldicellulosiruptor hydrothermalis 108T, Caldicellulosiruptor bescii DSM 6725T and Caldicellulosiruptor kronotskyensis 2002T. The 16S rRNA gene sequence of strain YA01T shares less than 98.1 % identity to the known Caldicellulosiruptor species. The G+C content of the genomic DNA was 34.8 mol%. Strain YA01T shares low genome-wide average nucleotide identity (90.31-91.10 %), average amino acid identity (91.45-92.10 %) and <70 % digital DNA-DNA hybridization value (41.8-44.2 %) with the three related species of the genus Caldicellulosiruptor. Strain YA01T grew at 50-78 °C (optimum, 70 °C) and at pH 5.0-9.5 (optimum, pH 6.5). Strain YA01T mainly produced acetate by consuming d(+)-glucose as a carbon source. The main cellular fatty acids were iso-C17 : 0 (35.7 %), C16 : 0 (33.3 %), DMA16 : 0 (6.6 %) and iso-C15 : 0 (5.9 %). Based on its distinct phylogenetic position, biochemical and physiological characteristics, and the major cellular fatty acids, strain YA01T is considered to represent a novel species of the genus Caldicellulosiruptor for which the name Caldicellulosiruptor diazotrophicus sp. nov. is proposed (type strain YA01T=DSM 112098T=JCM 34253T).

Nitrite as a causal factor for nitrate-dependent anaerobic corrosion of metallic iron induced by Prolixibacter strains.

Microbially influenced corrosion (MIC) may contribute significantly to overall corrosion risks, especially in the gas and petroleum industries. In this study, we isolated four Prolixibacter strains, which belong to the phylum Bacteroidetes, and examined their nitrate respiration- and Fe0 -corroding activities, together with two previously isolated Prolixibacter strains. Four of the six Prolixibacter strains reduced nitrate under anaerobic conditions, while the other two strains did not. The anaerobic growth of the four nitrate-reducing strains was enhanced by nitrate, which was not observed in the two strains unable to reduce nitrate. When the nitrate-reducing strains were grown anaerobically in the presence of Fe0 or carbon steel, the corrosion of the materials was enhanced by more than 20-fold compared to that in aseptic controls. This enhancement was not observed in cultures of the strains unable to reduce nitrate. The oxidation of Fe0 in the anaerobic cultures of nitrate-reducing strains occurred concomitantly with the formation of nitrite. Since nitrite chemically oxidized Fe0 under anaerobic and aseptic conditions, the corrosion of Fe0 - and carbon steel by the nitrate-reducing Prolixibacter strains was deduced to be mainly enhanced via the biological reduction of nitrate to nitrite, followed by the chemical oxidation of Fe0 to Fe2+ and Fe3+ coupled to the reduction of nitrite.

Fluviispira sanaruensis sp., nov., Isolated from a Brackish Lake in Hamamatsu, Japan.

Strain RF1110005T, which was isolated from brackish lake water sampled at Lake Sanaru in Japan as a "filterable" bacterial strain, was characterized as a novel species in the genus Fluviispira, family Silvanigrellaceae, order Silvanigrellales, the class Oligoflexia and the phylum Bdellovibrionota. Cells of RF1110005T were aerobic, Gram stain negative, and show a pleomorphic morphology of spiral, filamentous and rod shapes. Catalase reaction was positive. Strain RF1110005T grew optimally at 30 °C, pH 7.0-8.0 and 0.5% NaCl (w/v). The major polar lipids in RF1110005T were phosphatidylethanolamine and phosphatidylglycerol. The predominant cellular fatty acids were iso-C15:0 and anteiso-C15:0. Phylogenetic analysis based on 16S rRNA gene sequences and concatenates of core gene sequence showed that the nearest neighbor of strain RF1110005T was Fluviispira multicolorata strain 33A1-SZDPT with 98.4% 16S rRNA gene sequence similarity. The genome size of strain RF1110005T was 3.5 Mbp with two plasmids (80 kb and 69 kb), and the G + C content was 33.7 mol%. Comparisons with genome-wide analyses and chemotaxonomic characters clearly showed that strain RF1110005T differed from F. multicolorata. Therefore, a novel species in Fluviispira sanaruensis, sp. nov., is proposed for strain RF1110005T (= JCM 31447 T = LMG 30360 T).

Coprobacter secundus subsp. similis subsp. nov. and Solibaculum mannosilyticum gen. nov., sp. nov., isolated from human feces.

An obligately anaerobic, Gram-stain-negative, rod-shaped bacterium, designated strain 2CBH44T , was isolated from the fecal sample of a healthy Japanese man. This strain was initially assigned as a novel species of the genus Coprobacter based on the 16S rRNA gene sequence similarities compared with other Coprobacter species. The 16S rRNA gene sequence analysis revealed strain 2CBH44T had relatively low 16S rRNA gene sequence similarity (97.5%) to Coprobacter secundus 177T . However, strain 2CBH44T showed 96.9% average nucleotide identity value with C. secundus 177T , indicating that strain 2CBH44T and C. secundus 177T belong to the same species. On the other hand, the digital DNA-DNA hybridization value between strain 2CBH44T and C. secundus 177T was 73.5%, indicating that strain 2CBH44T is a subspecies of C. secundus. Another anaerobic, Gram-stain-variable, rod-shaped bacterium, designated strain 12CBH8T , was also isolated from human feces. Strain 12CBH8T had significantly low 16S rRNA gene sequence similarities (<92.0%) to the validated bacterial species within the family Oscillospiraceae. The percentage of conserved protein values between the genome of strain 12CBH8T and that of the validated related taxa were <50%, suggesting that strain 12CBH8T belongs to a novel genus. On the basis of the collected data, strain 2CBH44T represents a novel subspecies of C. secundus, for which the name Coprobacter secundus subsp. similis subsp. nov. (type strain 2CBH44T = JCM 34079T = DSM 111570T ) is proposed. Strain 12CBH8T represents a novel species of a novel genus, for which the name Solibaculum mannosilyticum gen. nov., sp. nov. (type strain 12CBH8T = JCM 34081T = DSM 111571T ) is proposed.

Iodidimonas gelatinilytica sp. nov., aerobic iodide-oxidizing bacteria isolated from brine water and surface seawater.

Chemo-organotrophic iodide (I-)-oxidizing bacterial strains Hi-2T and Mie-1 were isolated from iodide-rich natural gas brine water in Chiba and surface seawater in Mie, Japan, respectively. Cells of strains Hi-2T and Mie-1 were aerobic, Gram-negative and rod-shaped (0.3-0.5 µm width and 1.2-4.4 µm in length). Two isolates grew optimally at 30 °C, pH 7.5 and with 3% NaCl (w/v). Iodide oxidation to form molecular iodine (I2) was a biochemically unique trait for strains Hi-2T and Mie-1. The major cellular fatty acids are C18:1ω7c, C16:1ω5c and C18:1 2-OH. A phylogenetic analysis based on the 16S rRNA gene sequence revealed that strains Hi-2T and Mie-1 were located near Iodidimonas muriae C-3T with 99.2% sequence similarity. The calculated digital DNA-DNA hybridization (dDDH) value of 65.7-65.9% between the two isolates and I. muriae C-3T was lower than the threshold of 70%, which was used for prokaryotic species delineation. Strains Hi-2T and Mie-1 differed in the hydrolysis of aesculin, the hydrolysis of gelatin and the major cellular fatty acids composition from I. muriae C-3T. Considering these biochemical properties, the major cellular fatty acids composition and dDDH value, a novel species is proposed for strains Hi-2T (= JCM 17844T = LMG 28661T) and Mie-1 (= JCM 17845 = LMG 28662), to be named Iodidimonas gelatinilytica.

Possible Involvement of a Tetrathionate Reductase Homolog in Dissimilatory Arsenate Reduction by Anaeromyxobacter sp. Strain PSR-1.

Anaeromyxobacter sp. strain PSR-1, a dissimilatory arsenate [As(V)]-reducing bacterium, can utilize As(V) as a terminal electron acceptor for anaerobic respiration. A previous draft genome analysis revealed that strain PSR-1 lacks typical respiratory As(V) reductase genes (arrAB), which suggested the involvement of another protein in As(V) respiration. Dissimilatory As(V) reductase activity of strain PSR-1 was induced under As(V)-respiring conditions and was localized predominantly in the periplasmic fraction. The activity was visualized by partially denaturing gel electrophoresis, and liquid chromatography-tandem mass spectrometry analysis identified proteins involved in the active band. Among these proteins, a protein annotated as molybdopterin-dependent oxidoreductase (PSR1_00330) exhibited the highest sequence coverage, 76%. Phylogenetic analysis revealed that this protein was a homolog of tetrathionate reductase catalytic subunit TtrA. However, the crude extract of strain PSR-1 did not show significant tetrathionate reductase enzyme activity. Comparative proteomic analysis revealed that the protein PSR1_00330 and a homolog of tetrathionate reductase electron transfer subunit TtrB (PSR1_00329) were expressed abundantly and specifically under As(V)-respiring conditions, respectively. The genes encoding PSR1_00330 and PSR1_00329 formed an operon-like structure along with a gene encoding a c-type cytochrome (cyt c), and their transcription was upregulated under As(V)-respiring conditions. These results suggest that the protein PSR1_00330, which lacks tetrathionate reductase activity, functions as a dissimilatory As(V) reductase in strain PSR-1. Considering the wide distribution of TtrA homologs among bacteria and archaea, they may play a hitherto unknown role along with conventional respiratory As(V) reductase (Arr) in the biogeochemical cycling of arsenic in nature.IMPORTANCE Dissimilatory As(V)-reducing prokaryotes play significant roles in arsenic release and contamination in groundwater and threaten the health of people worldwide. Generally, such prokaryotes reduce As(V) by means of a respiratory As(V) reductase designated Arr. However, some dissimilatory As(V)-reducing prokaryotes such as Anaeromyxobacter sp. strain PSR-1 lack genes encoding Arr, suggesting the involvement of other protein in As(V) reduction. In this study, using multiple proteomic and transcriptional analyses, it was found that the dissimilatory As(V) reductase of strain PSR-1 was a protein closely related to the tetrathionate reductase catalytic subunit (TtrA). Tetrathionate reductase is known to play a role in anaerobic respiration of Salmonella on tetrathionate, but strain PSR-1 showed neither growth on tetrathionate nor significant tetrathionate reductase enzyme activity. These results suggest the possibility that TtrA homologs encoded in a wide variety of archaeal and bacterial genomes might function as dissimilatory As(V) reductases.

Microbial interaction between the succinate-utilizing bacterium Phascolarctobacterium faecium and the gut commensal Bacteroides thetaiotaomicron.

A large variety of microbes are present in the human gut, some of which are considered to interact with each other. Most of these interactions involve bacterial metabolites. Phascolarctobacterium faecium hardly uses carbohydrates for growth and instead uses succinate as a substrate. This study investigated the growth behavior of the co-culture of the succinate-specific utilizer P. faecium and the succinogenic gut commensal Bacteroides thetaiotaomicron. Succinate production by B. thetaiotaomicron supported the growth of P. faecium and concomitant propionate production via the succinate pathway. The succinate produced was completely converted to propionate. This result was comparable with the monoculture of P. faecium in the medium supplemented with 1% (w/v) succinate. We analyzed the transcriptional response (RNA-Seq) between the mono- and co-culture of P. faecium and B. thetaiotaomicron. Comparison of the expression levels of genes of P. faecium between the mono- and co-cultured conditions highlighted that the genes putatively involved in the transportation of succinate were notably expressed under the co-cultured conditions. Differential expression analysis showed that the presence of P. faecium induced changes in the B. thetaiotaomicron transcriptional pattern, for example, expression changes in the genes for vitamin B12 transporters and reduced expression of glutamate-dependent acid resistance system-related genes. Also, transcriptome analysis of P. faecium suggested that glutamate and succinate might be used as sources of succinyl-CoA, an intermediate in the succinate pathway. This study revealed some survival strategies of asaccharolytic bacteria, such as Phascolarctobacterium spp., in the human gut.

Amedibacterium intestinale gen. nov., sp. nov., isolated from human faeces, and reclassification of Eubacterium dolichum Moore et al. 1976 (Approved Lists 1980) as Amedibacillus dolichus gen. nov., comb. nov.

Four strains (9CBEGH2T, 9BBH35, 6BBH38 and 6EGH11) of Gram-stain-positive, obligately anaerobic, rod-shaped bacteria were isolated from faecal samples from healthy Japanese humans. The results of 16S rRNA gene sequence analysis indicated that the four strains represented members of the family Erysipelotrichaceae and formed a monophyletic cluster with 'Absiella argi' strain N6H1-5 (99.4% sequence similarity) and Eubacterium sp. Marseille-P5640 (99.3 %). Eubacterium dolichum JCM 10413T (94.2 %) and Eubacterium tortuosum ATCC 25548T (93.7 %) were located near this monophyletic cluster. The isolates, 9CBEGH2T, 'A. argi' JCM 30884 and Eubacterium sp. Marseille-P5640 shared 98.7-99.1% average nucleotide identity (ANI) with each other. Moreover, the in silico DNA-DNA hybridization (DDH) values among three strains were 88.4-90.6%, indicating that these strains represent the same species. Strain 9CBEGH2T showed 21.5-24.1 % in silico DDH values with other related taxa. In addition, the ANI values between strain 9CBEGH2T and other related taxa ranged from 71.2 % to 73.5 %, indicating that this strain should be considered as representing a novel species on the basis of whole-genome relatedness. Therefore, we formally propose a novel name for 'A. argi' strains identified because the name 'A. argi' has been effectively, but not validly, published since 2017. On the basis of the collected data, strain 9CBEGH2T represents a novel species of a novel genus, for which the name Amedibacterium intestinale gen. nov., sp. nov. is proposed. The type strain of A. intestinale is 9CBEGH2T (=JCM 33778T=DSM 110575T).

Chryseotalea sanaruensis gen. nov., sp., nov., a Member of the Family Cytophagaceae, Isolated from a Brackish Lake in Hamamatsu Japan.

A strain-designated YsT was isolated as a filterable bacterial strain from Lake Sanaru, a brackish water lake in Hamamatsu Japan. YsT is aerobic, Gram-negative, and slender rod shaped. YsT grew optimally at 30 °C, pH 7.0-8.0 and without the addition of NaCl. MK-7 was the sole isoprenoid quinone. The main cellular polar lipids were phosphatidylethanolamine and unidentified amino- and polar-lipids. The predominant cellular fatty acids were C18:0, iso-C14:0 and iso-C15:0. Phylogenetic analysis of 16S rRNA gene sequence revealed the nearest neighbours of strain YsT to be members of the Ohtaekwangia and Chryseolinea genera with 91.2-92.1% sequence similarity. The percentages of conserved proteins (POCP) between the genomes of YsT and related strains were less than 50%. Phenotypic analyses suggested that YsT could not metabolize glucose and related sugars, which was discriminative from its phylogenetic relatives. We, therefore, propose a novel species in a new genus, Chryseotalea sanaruensis gen. nov., sp. nov. in the family Cytophagaceae (= JCM 30318T = LMG 30359T), based on cell size, the predominant cellular fatty acid composition, and the DNA GC content (38.9 mol%).