Analysis of 1,000+ Type-Strain Genomes Substantially Improves Taxonomic Classification of Alphaproteobacteria

Salipiger mangrovisoli sp. nov., isolated from mangrove soil and the proposal for the reclassification of Paraphaeobacter pallidus as Salipiger pallidus comb. nov

A novel Gram-stain-negative, aerobic and rod-shaped bacterial strain designated as 6D45A^T was isolated from mangrove soil and characterized using a polyphasic taxonomic approach. Strain 6D45A^T was found to grow at 10-37 °C (optimum, 28 °C), at pH 6.0-9.0 (optimum, 7.0) and in 0-5 % (w/v) NaCl (optimum, 2%). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain 6D45A^T fell into the genus Salipiger and shared 99.1 % identity with the closest type strain Salipiger pacificus CGMCC 1.3455^T and less than 97.2 % identity with other type strains of this genus. The 34.8 % digital DNA-DNA hybridization (dDDH) and 88.3 % average nucleotide identity (ANI) values between strain 6D45A^T and the closest relative above were well below recognized thresholds of 70 % DDH and 95-96 % ANI for species definition, implying that strain 6D45A^T should represent a novel genospecies. The phylogenomic analysis indicated that strain 6D45A^T formed an independent branch distinct from reference strains. The predominant cellular fatty acid of strain 6D45A^T was summed feature 8 (C_18 : 1  ω6c and/or C_18 : 1  ω7c, 66.9 %); the polar lipids were diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, two unidentified aminolipids, two unidentified glycolipids and an unknown lipid; the respiratory quinone was Q-10. The genomic DNA G+C content was 66.5 mol %. Based on the phenotypic and genotypic characteristics, strain 6D45A^T is concluded to represent a novel species of the genus Salipiger, for which the name Salipiger mangrovisoli sp. nov., is proposed. The type strain of the species is 6D45A^T (=GDMCC 1.1960^T=KCTC 82334^T). We also propose the reclassification of Paraphaeobacter pallidus as Salipiger pallidus comb. nov. and 'Pelagibaca abyssi' as a species of the genus Salipiger.

Glacieibacterium frigidum gen. nov., sp. nov., a novel member of the family Sphingosinicellaceae isolated from a glacier

A novel Gram-stain-negative, rod-shaped, yellow bacterium, designated as LB1R16^T, was isolated from the Laigu glacier on the Tibetan Plateau, PR China. Strain LB1R16^T was catalase-positive, oxidase-negative and grew at 0-28 °C, pH 6.0-8.0 and in the absence of NaCl. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain LB1R16^T belongs to the family Sphingosinicellaceae but formed an independent lineage. The highest level of 16S rRNA gene sequence similarities were found to Polymorphobacter arshaanensis DJ1R-1^T (95.24 %), Sphingoaurantiacus capsulatus YLT33^T (94.78 %) and Sandarakinorhabdus limnophila DSM 17366^T (94.67 %). The genomic DNA G+C content was 68.8 mol%. The main cellular fatty acids were summed feature 8 (C_18 : 1  ω7c/C_18 : 1  ω6c), summed feature 3 (C_16 : 1  ω7c/C_16 : 1  ω6c), C_16 : 0 and C_12 : 0-OH. The respiratory quinone was ubiquinone-10. The polar lipids were phosphatidylethanolamine, phosphatidylglycerol, one sphingoglycolipid, one unidentified aminolipid, one unidentified phospholipid and two unidentified polar lipids, which were different from the type strains of Polymorphobacter arshaanensis, Sphingoaurantiacus capsulatus and Sandarakinorhabdus limnophila. Based on a polyphasic approach, a novel species of a new genus, Glacieibacterium frigidum gen. nov., sp. nov., within the family Sphingosinicellaceae is proposed. The type strain is LB1R16^T (=CGMCC 1.11941^T=NBRC 113873^T).

TCA Cycle Replenishing Pathways in Photosynthetic Purple Non-Sulfur Bacteria Growing with Acetate

Purple non-sulfur bacteria (PNSB) are anoxygenic photosynthetic bacteria harnessing simple organic acids as electron donors. PNSB produce a-aminolevulinic acid, polyhydroxyalcanoates, bacteriochlorophylls a and b, ubiquinones, and other valuable compounds. They are highly promising producers of molecular hydrogen. PNSB can be cultivated in organic waste waters, such as wastes after fermentation. In most cases, wastes mainly contain acetic acid. Therefore, understanding the anaplerotic pathways in PNSB is crucial for their potential application as producers of biofuels. The present review addresses the recent data on presence and diversity of anaplerotic pathways in PNSB and describes different classifications of these pathways.

Draft Genome Sequence of Novel Filterable Rhodospirillales Bacterium Strain TMPK1, Isolated from Soil

We report the draft genome sequence of novel Rhodospirillales bacterium strain TMPK1, isolated from a micropore-filtered soil suspension. This strain has a genome of 4,249,070 bp, comprising 4,151 protein-coding sequences. The genome sequence data further suggest that strain TMPK1 is an alphaproteobacterium capable of carotenoid production.

Proteome, bioinformatic and functional analyses reveal a distinct and conserved metabolic pathway for bile salt degradation in the Sphingomonadaceae

Bile salts are amphiphilic steroids chain with digestive functions in vertebrates. Upon excretion, bile salts are degraded by environmental bacteria. Degradation of the bile-salt steroid skeleton resembles the well-studied pathway for other steroids like testosterone, while specific differences occur during side-chain degradation and the initiating transformations of the steroid skeleton. Of the latter, two variants via either Δ^1,4- or Δ^4,6-3-ketostructures of the steroid skeleton exist for 7-hydroxy bile salts. While the Δ^1,4- variant is well-known from many model organisms, the Δ^4,6-variant involving a 7-hydroxysteroid dehydratase as key enzyme has not been systematically studied. Here, combined proteomic, bioinformatic and functional analyses of the Δ^4,6-variant in Sphingobium sp. strain Chol11 were performed. They revealed a degradation of the steroid rings similar to the Δ^1,4-variant except for the elimination of the 7-OH as a key difference. In contrast, differential production of the respective proteins revealed a putative gene cluster degradation of the C₅ carboxylic side chain encoding a CoA-ligase, an acyl-CoA dehydrogenase, a Rieske monooxygenase, and an amidase, but lacking most canonical genes known from other steroid-degrading bacteria. Bioinformatic analyses predicted the Δ^4,6-variant to be widespread among the Sphingomonadaceae, which was verified for three type strains which also have the predicted side-chain degradation cluster. A second amidase in the side-chain degradation gene cluster of strain Chol11 was shown to cleave conjugated bile salts while having low similarity to known bile-salt hydrolases. This study signifies members of the Sphingomonadaceae remarkably well-adapted to the utilization of bile salts via a partially distinct metabolic pathway. Importance This study highlights the biochemical diversity of bacterial degradation of steroid compounds, in particular bile salts. Furthermore, it substantiates and advances knowledge of a variant pathway for degradation of steroids by sphingomonads, a group of environmental bacteria that are well-known for their broad metabolic capabilities. Biodegradation of bile salts is a critical process due to the high input of these compounds from manure into agricultural soils and wastewater treatment plants. In addition, these results may also be relevant for the biotechnological production of bile salts or other steroid compounds with pharmaceutical functions.

Curvivirga aplysinae gen. nov., sp. nov., a marine bacterium isolated from the sea sponge Aplysina fistularis

A Gram-stain-negative, strictly aerobic, motile bacterium, designated strain RKSG073^T, was isolated from the sea sponge Aplysina fistularis, collected off the west coast of San Salvador, The Bahamas. Cells were curved-to-spiral rods with single, bipolar (amphitrichous) flagella, oxidase- and catalase-positive, non-nitrate-reducing and required salt for growth. RKSG073^T grew optimally at 30-37 °C, pH 6-7, and with 2-3 % (w/v) NaCl. The predominant fatty acids of RKSG073^T were summed feature 8 (C_18 : 1ω6c and/or C_18 : 1ω7c) and C_16 : 0. Major isoprenoid quinones were identified as Q-10 and Q-9. Phylogenetic analyses of nearly complete 16S rRNA genes and genome sequences positioned strain RKSG073^T in a clade with its closest relative Aestuariispira insulae AH-MY2^T (92.1 % 16S rRNA gene sequence similarity), which subsequently clustered with Hwanghaeella grinnelliae Gri0909^T, Marivibrio halodurans ZC80^T and type species of the genera Kiloniella, Thalassospira and Terasakiella. The DNA G+C content calculated from the genome of RKSG073^T was 42.2 mol%. On the basis of phylogenetic distinctiveness and polyphasic analysis, here we propose that RKSG073^T (culture deposit numbers: ATCC collection = TSD-74^T, BCCM collection = LMG 29869^T) represents the type strain of a novel genus and species within the family Kiloniellaceae, order Rhodospirillales and class Alphaproteobacteria, for which the name Curvivirga aplysinae gen. nov., sp. nov. is proposed.

Salibaculum halophilum gen. nov., sp. nov. and Salibaculum griseiflavum sp. nov., in the family Rhodobacteraceae

Two Gram-stain-negative, moderately halophilic, non-motile, rod-shaped, pale yellow, and aerobic strains, designated WDS1C4^T and WDS4C29^T, were isolated from a marine solar saltern in Weihai, Shandong Province, PR China. Growth of strain WDS1C4^T occurred at 10-45 °C (optimum, 37 °C), with 4-16 % (w/v) NaCl (optimum, 8 %) and at pH 6.5-9.0 (optimum, pH 7.5). Growth of strain WDS4C29^T occurred at 10-45 °C (optimum, 40 °C), with 2-18 % (w/v) NaCl (optimum, 6 %) and at pH 6.5-9.0 (optimum, pH 7.5). Q-10 was the sole respiratory quinone of the two strains. The major polar lipids of strains WDS1C4^T and WDS4C29^T were phosphatidylglycerol, phosphatidylethanolamine and phosphatidylcholine. The major cellular fatty acid in strains WDS1C4^T and WDS4C29^T was C_18 : 1  ω7c, and the genomic DNA G+C contents of strains WDS1C4^T and WDS4C29^T were 67.6 and 63.3 mol%, respectively. Phylogenetic analyses based on 16S rRNA gene sequences indicated that strains WDS1C4^T and WDS4C29^T were members of the family Rhodobacteraceae and showed 94.3 and 95.3 % similarities to their closest relative, Celeribacter indicus, respectively. The similarity between WDS1C4^T and WDS4C29^T was 97.3 %. Differential phenotypic and genotypic characteristics of the two isolates from recognized genera showed that the two strains should be classified as representing two novel species in a new genus for which the names Salibaculum halophilum gen. nov., sp. nov. (type species, type strain WDS1C4^T=MCCC 1H00179^T=KCTC 52542^T) and Salibaculum griseiflavum sp. nov. (WDS4C29^T=MCCC 1H00175^T=KCTC 52541^T) are proposed.

Muriiphilus fusiformis gen. nov., sp. nov., a novel non-marine bacterium belonging to the Roseobacter group, and reclassification of Maritimibacter lacisalsi (Zhong et al. 2015) as Muriicola lacisalsi gen. nov., comb. nov

An aerobic, Gram-stain-negative, non-sporulating, flagellated and spindle-like bacterium, designated HY14^T, was isolated from a pickle-processing factory wastewater sample. The isolate chemoheterotrophically grew at 4-42 °C (optimum, 35 °C) and pH 5.5-9.0 (optimum, pH 6.0-6.5). Salt was required for growth (0.5-12 % NaCl, w/v). A deep brown and water-soluble uncharacterized pigment was produced when grown in certain media. The predominant fatty acids (>5 %) included C_16 : 0, C_18 : 1  ω7c, 11-methyl C_18 : 1  ω7c and C_19 : 0 cyclo ω8c. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine, two unidentified aminolipids, two unidentified phospholipids, two unidentified glycolipids and five unknown lipids. The major isoprenoid quinone was ubiquinone-10. Pairwise alignment based on 16S rRNA gene sequences indicated that strain HY14^T had the highest sequence similarity to genera Maritimibacter (95.61-96.05 %) and Boseongicola (95.82 %). Phylogenetic analysis based on core genome illustrated that strain HY14^T formed a monophyletic lineage with members of the genus Maritimibacter in the clade of the Roseobacter group in the family Rhodobacteraeceae. The core-gene average amino acid identity used to define bacterial genera by a threshold of 60-80 % was calculated to be 68.56-76.5 % between HY14^T and closely related taxa. Several genomic characteristics, such as carrying two RuBisCO-mediated pathways and different osmoprotectant transport pathways, exhibited the genotypic discrepancies of strain HY14^T. Based on the polyphasic taxonomic characterization, strain HY14^T is considered to represent a novel species of a novel genus belonging to the family Rhodobacteraeceae, for which the name Muriiphilus fusiformis gen. nov., sp. nov. is proposed. The type strain is HY14^T (=CGMCC 1.15973^T=KCTC 52499^T). Maritimibacter lacisalsi (Zhong et al. 2015) is considered to diverge from Maritimibacter alkaliphilus at the genus level, and should be reassigned as a novel genus, for which the name Muriicola lacisalsi gen. nov., comb. nov. is proposed.

Exploring the Potential of Micrococcus luteus Culture Supernatant With Resuscitation-Promoting Factor for Enhancing the Culturability of Soil Bacteria

A bacterial species is best characterized after its isolation in a pure culture. This is an arduous endeavor for many soil microorganisms, but it can be simplified by several techniques for improving culturability: for example, by using growth-promoting factors. We investigated the potential of a Micrococcus luteus culture supernatant containing resuscitation-promoting factor (SRpf) to increase the number and diversity of cultured bacterial taxa from a nutrient-rich compost soil. Phosphate-buffered saline and inactivated SRpf were included as controls. After agitation with SRpf at 28°C for 1 day, the soil suspension was diluted and plated on two different solid, oligotrophic media: tenfold diluted Reasoner’s 2A agar (R2A) and soil extract-based agar (SA). Colonies were collected from the plates to assess the differences in diversity between different treatments and cultivation media. The diversity on both R2A and SA was higher in the SRpf-amended extracts than the controls, but the differences on R2A were higher. Importantly, 51 potentially novel bacterial species were isolated on R2A and SA after SRpf treatment. Diversity in the soil extracts was also determined by high-throughput 16S rRNA amplicon sequencing, which showed an increase in the abundance of specific taxa before their successful cultivation. Conclusively, SRpf can effectively enhance the growth of soil bacterial species, including those hitherto uncultured.

Roseobacters in a Sea of Poly- and Paraphyly: Whole Genome-Based Taxonomy of the Family Rhodobacteraceae and the Proposal for the Split of the "Roseobacter Clade" Into a Novel Family, Roseobacteraceae fam. nov

The family Rhodobacteraceae consists of alphaproteobacteria that are metabolically, phenotypically, and ecologically diverse. It includes the roseobacter clade, an informal designation, representing one of the most abundant groups of marine bacteria. The rapid pace of discovery of novel roseobacters in the last three decades meant that the best practice for taxonomic classification, a polyphasic approach utilizing phenotypic, genotypic, and phylogenetic characteristics, was not always followed. Early efforts for classification relied heavily on 16S rRNA gene sequence similarity and resulted in numerous taxonomic inconsistencies, with several poly- and paraphyletic genera within this family. Next-generation sequencing technologies have allowed whole-genome sequences to be obtained for most type strains, making a revision of their taxonomy possible. In this study, we performed whole-genome phylogenetic and genotypic analyses combined with a meta-analysis of phenotypic data to review taxonomic classifications of 331 type strains (under 119 genera) within the Rhodobacteraceae family. Representatives of the roseobacter clade not only have different environmental adaptions from other Rhodobacteraceae isolates but were also found to be distinct based on genomic, phylogenetic, and in silico-predicted phenotypic data. As such, we propose to move this group of bacteria into a new family, Roseobacteraceae fam. nov. In total, reclassifications resulted to 327 species and 128 genera, suggesting that misidentification is more problematic at the genus than species level. By resolving taxonomic inconsistencies of type strains within this family, we have established a set of coherent criteria based on whole-genome-based analyses that will help guide future taxonomic efforts and prevent the propagation of errors.

Methylobrevis albus sp. nov., isolated from freshwater lake sediment

An aerobic, Gram-stain-negative, rod-shaped bacterium with flagellum, designated L22^T, was isolated from sediment of Hulun Lake, Inner Mongolia, China. The organism was found to grow optimally at 30° C in a medium containing 0-0.75% (w/v) NaCl at pH 7.5. The major fatty acid identified was summed feature 8 (C_18:1ω7c). The dominant polar lipids were phosphomonoester, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylcholine. The main respiratory quinone was Q-10. The draft genome sequence of strain L22^T consisted of 4354,788 bp. The G + C content of genomic DNA was 69.8 mol %. The 16S rRNA gene sequences indicated that strain L22^T was affiliated with the genus Methylobrevis within the family Pleomorphomonadaceae, being most closely related to Methylobrevis pamukkalensis JCM 30229^T with 95.9% 16S rRNA gene sequences similarity. The AAI, ANI and dDDH values between strain L22^T and M. pamukkalensis JCM 30229^T were 72.5%, 80.7% and 22.7%. Based on taxonomic results in this study, we proposed that strain L22^T a novel species in the genus Methylobrevis of the family Pleomorphomonadaceae, for which the name Methylobrevis albus sp. nov. is proposed. The type strain is L22^T (=KCTC 72858^T=MCCC 1H00432^T).

Phylogenomic Reconstruction and Metabolic Potential of the Genus Aminobacter

Bacteria belonging to the genus Aminobacter are metabolically versatile organisms thriving in both natural and anthropized terrestrial environments. To date, the taxonomy of this genus is poorly defined due to the unavailability of the genomic sequence of A. anthyllidis LMG 26462^T and the presence of unclassified Aminobacter strains. Here, we determined the genome sequence of A. anthyllidis LMG 26462^T and performed phylogenomic, average nucleotide identity and digital DNA-DNA hybridization analyses of 17 members of genus Aminobacter. Our results indicate that 16S rRNA-based phylogeny does not provide sufficient species-level discrimination, since most of the unclassified Aminobacter strains belong to valid Aminobacter species or are putative new species. Since some members of the genus Aminobacter can utilize certain C1 compounds, such as methylamines and methyl halides, a comparative genomic analysis was performed to characterize the genetic basis of some degradative/assimilative pathways in the whole genus. Our findings suggest that all Aminobacter species are heterotrophic methylotrophs able to generate the methylene tetrahydrofolate intermediate through multiple oxidative pathways of C1 compounds and convey it in the serine cycle. Moreover, all Aminobacter species carry genes implicated in the degradation of phosphonates via the C-P lyase pathway, whereas only A. anthyllidis LMG 26462^T contains a symbiosis island implicated in nodulation and nitrogen fixation.

Characterization and phylogenomic analysis of Breznakiella homolactica gen. nov. sp. nov. indicate that termite gut treponemes evolved from non-acetogenic spirochetes in cockroaches

Spirochetes of the genus Treponema are surprisingly abundant in termite guts, where they play an important role in reductive acetogenesis. Although they occur in all termites investigated, their evolutionary origin is obscure. Here, we isolated the first representative of 'termite gut treponemes' from cockroaches, the closest relatives of termites. Phylogenomic analysis revealed that Breznakiella homolactica gen. nov. sp. nov. represents the most basal lineage of the highly diverse 'termite cluster I', a deep-branching sister group of Treponemataceae (fam. 'Termitinemataceae') that was present already in the cockroach ancestor of termites and subsequently coevolved with its host. Breznakiella homolactica is obligately anaerobic and catalyses the homolactic fermentation of both hexoses and pentoses. Resting cells produced acetate in the presence of oxygen. Genome analysis revealed the presence of pyruvate oxidase and catalase, and a cryptic potential for the formation of acetate, ethanol, formate, CO₂ and H₂ - the fermentation products of termite gut isolates. Genes encoding key enzymes of reductive acetogenesis, however, are absent, confirming the hypothesis that the ancestral metabolism of the cluster was fermentative, and that the capacity for acetogenesis from H₂ plus CO₂ - the most intriguing property among termite gut treponemes - was acquired by lateral gene transfer.

Harenicola maris gen. nov., sp. nov. isolated from the Sea of Japan shallow sediments

A Gram-negative, non-motile bacterium КMM 3653^T was isolated from a sediment sample from the Sea of Japan seashore, Russia. On the basis of the 16S rRNA gene sequence analysis the strain КMM 3653^T was positioned within the family Rhodobacteraceae (class Alphaproteobacteria) forming a distinct lineage with the highest gene sequence similarities to the members of the genera Pacificibacter (95.2-94.7%) and Nioella (95.1-94.5%), respectively. According to the phylogenomic tree based on 400 conserved protein sequences, strain КMM 3653^T was placed in the cluster comprising Vannielia litorea, Nioella nitratireducens, Litoreibacter albidus and Pseudoruegeria aquimaris as a separate lineage adjacent to V. litorea KCTC 32083^T. The average nucleotide identity values between strain КMM 3653^T and V. litorea KCTC 32083^T, N. nitratireducens KCTC 32417^T, L. albidus KMM 3851^T, and P. aquimaris CECT 7680^T were 71.1, 70.3, 69.6, and 71.0%, respectively. Strain КMM 3653^T contained Q-10 as the predominant ubiquinone and C_18:1ω7c as the major fatty acid followed by C_16:0. The polar lipids were phosphatidylcholine, phosphatidylglycerol, diphosphatidylglycerol, an unidentified phospholipid, two unidentified aminolipids, and five unidentified lipids. The DNA G+C content of 61.8% was calculated from the genome sequence. Based on the phylogenetic evidence and distinctive phenotypic characteristics, we proposed strain KMM 3653^T (= KCTC 82575^T) to be classified as a novel genus and species Harenicola maris gen. nov., sp. nov.

Isolation of Thalassobius mangrovi sp. nov., a novel bacterium in the family Rhodobacteraceae, from marine mangrove sediment

A Gram-stain-negative, strictly aerobic and oval-shaped bacterial strain with a flagellum, designated GS-10^T, was isolated from mangrove wetland sediment. GS-10^T grew at 20-40 °C (optimum, 37 °C), in the pH range of 5.0-11.0 (optimum, 6.0-8.0) and under various NaCl concentrations from 1 to 11 % (w/v) (optimum, 5-6 %). The respiratory quinone was ubiquinone-10, and the predominant polar lipids were phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol. The major fatty acids (>10 % of the total fatty acids) were summed feature 4 (C_17 : 1iso I/anteiso B) and summed feature 8 (C_18 : 1ω7c and/or C_18 : 1ω6c). The G+C content of the genomic DNA was 63.71 %. On the basis of the results from comparative analysis of the 16S rRNA gene sequence, GS-10^T represents a member of the family Rhodobacteraceae and had the highest sequence similarity to Thalassobius gelatinovorus CECT 4357^T (97.47 %), followed by Lutimaribacter pacificus W11-2B^T (97.03 %), Marivita cryptomonadis CL-SK44^T (96.83 %), Thalassobius autumnalis CECT 5118^T (96.75 %) and Thalassobius mediterraneus CECT 5383^T (96.68 %). Phylogenetic trees based on 16S rRNA gene sequences, multilocus sequence analysis (MLSA) and whole genome sequences revealed that GS-10^T clustered with species within the genus Thalassobius. The average nucleotide identity (ANI) and the average amino acid identity (AAI) values were calculated from complete genome sequences and indicated that GS-10^T represented a novel species of the genus Thalassobius, and the name Thalassobius mangrovi sp. nov. is proposed for this species. The type strain of Thalassobius mangrovi is GS-10^T (=MCCC 1K03624^T=KCTC 82131^T).

Peteryoungia gen. nov. with four new species combinations and description of Peteryoungia desertarenae sp. nov., and taxonomic revision of the genus Ciceribacter based on phylogenomics of Rhizobiaceae

A novel bacterial strain designated as ADMK78^T was isolated from the saline desert soil. The cells were rod-shaped, Gram-stain-negative, and non-motile. The strain ADMK78^T grows best at 28 °C. Phylogeny of 16S rRNA gene placed the strain ADMK78^T with the members of genera Ciceribacter and Rhizobium, while the highest sequence similarity was with Rhizobium wuzhouense W44^T (98.7%) and Rhizobium ipomoeae shin9-1 ^T (97.9%). Phylogenetic analysis based on 92 core-genes extracted from the genome sequences and average amino acid identity (AAI) revealed that the strain ADMK78^T forms a distinct cluster including five species of Rhizobium, which is separate from the cluster of the genera Rhizobium and Ciceribacter. We propose re-classification of Rhizobium ipomoeae, R. wuzhouense, R. rosettiformans and R. rhizophilum into the novel genus Peteryoungia. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values of ADMK78^T were less than 82 and 81%, respectively, among all type strains included in the genus Peteryoungia. The strain ADMK78^T showed differences in physiological, phenotypic, and protein profiles estimated by MALDI-TOF MS to its closest relatives. Based on the phenotypic, chemotaxonomic properties, and phylogenetic analyses, the strain ADMK78^T represents a novel species, Peteryoungia desertarenae sp. nov. The type strain is ADMK78^T (= MCC 3400^T; KACC 21383^T; JCM 33657^T). We also proposed the reclassification of Rhizobium daejeonense, R. naphthalenivorans and R. selenitireducens, into the genus Ciceribacter, based on core gene phylogeny and AAI values.

Kaustia mangrovi gen. nov., sp. nov. isolated from Red Sea mangrove sediments belongs to the recently proposed Parvibaculaceae family within the order Rhizobiales

We isolated a novel strain, R1DC25T, described as Kaustia mangrovi gen. nov. sp. nov. from the sediments of a mangrove forest on the coast of the Red Sea in Saudi Arabia. This isolate is a moderately halophilic, aerobic/facultatively anaerobic Gram-stain-negative bacterium showing optimum growth at between 30 and 40 °C, at a pH of 8.5 and with 3-5 % NaCl. The genome of R1DC25T comprises a circular chromosome that is 4 630 536 bp in length, with a DNA G+C content of 67.3 mol%. Phylogenetic analyses based on the 16S rRNA gene sequence and whole-genome multilocus sequence analysis of 120 concatenated single-copy genes revealed that R1DC25T represents a distinct lineage within the family Parvibaculaceae in the order Rhizobiales within the class Alphaproteobacteria. R1DC25T showing 95.8, 95.3 and 94.5 % 16S rRNA gene sequence identity with Rhodoligotrophos appendicifer, Rhodoligotrophos jinshengii and Rhodoligotrophos defluvii, respectively. The predominant quinone was Q-10, and the polar lipids were phosphatidylglycerol, phosphatidylcholine, diphosphatidylglycerol, as well as several distinct aminolipids and lipids. The predominant cellular fatty acids were C19 : 0 cyclo ω8c, a combination of C18 : 1ω7c and/or C18 : 1ω6c and C16 : 0. On the basis of the differences in the phenotypic, physiological and biochemical characteristics from its known relatives and the results of our phylogenetic analyses, R1DC25T (=KCTC 72348T;=JCM 33619T;=NCCB 100699T) is proposed to represent a novel species in a novel genus, and we propose the name Kaustia mangrovi gen. nov., sp. nov. (Kaustia, subjective name derived from the abbreviation KAUST for King Abdullah University of Science and Technology; mangrovi, of a mangrove).

Elevated Atmospheric CO2 and Nitrogen Fertilization Affect the Abundance and Community Structure of Rice Root-Associated Nitrogen-Fixing Bacteria

Elevated atmospheric CO2 (eCO2) results in plant growth and N limitation, yet how root-associated nitrogen-fixing bacterial communities respond to increasing atmospheric CO2 and nitrogen fertilization (eN) during the growth stages of rice is unclear. Using the nifH gene as a molecular marker, we studied the combined effect of eCO2 and eN on the diazotrophic community and abundance at two growth stages in rice (tillering, TI and heading, HI). Quantitative polymerase chain reaction (qPCR) showed that eN had no obvious effect on nifH abundance in rice roots under either ambient CO2 (aCO2) or eCO2 treatment at the TI stage; in contrast, at the HI, nifH copy numbers were increased under eCO2 and decreased under aCO2. For rhizosphere soils, eN significantly reduced the abundance of nifH under both aCO2 and eCO2 treatment at the HI stage. Elevated CO2 significantly increased the nifH abundance in rice roots and rhizosphere soils with nitrogen fertilization, but had no obvious effect without N addition at the HI stage. There was a significant interaction [CO2 × N fertilization] effect on nifH abundance in root zone at the HI stage. In addition, the nifH copy numbers in rice roots were significantly higher at the HI stage than at the TI stage. Sequencing analysis indicated that the root-associated diazotrophic community structure tended to cluster according to the nitrogen fertilization treatment and that Rhizobiales were the dominant diazotrophs in all root samples at the HI stage. Additionally, nitrogen fertilization significantly increased the relative abundance of Methylosinus (Methylocystaceae) under eCO2 treatment, but significantly decreased the relative abundance of Rhizobium (Rhizobiaceae) under aCO2 treatment. Overall, the combined effect of eN and eCO2 stimulates root-associated diazotrophic methane-oxidizing bacteria while inhibits heterotrophic diazotrophs.

Emerging diversity and ongoing expansion of the genus Brucella

Remarkable genetic diversity and breadth of host species has been uncovered in the Brucella genus over the past decade, fundamentally changing our concept of what it means to be a Brucella. From ocean fishes and marine mammals, to pond dwelling amphibians, forest foxes, desert rodents, and cave-dwelling bats, Brucella have revealed a variety of previously unknown niches. Classical microbiological techniques have been able to help us classify many of these new strains but at times have limited our ability to see the true relationships among or within species. The closest relatives of Brucella are soil bacteria and the adaptations of Brucella spp. to live intracellularly suggest that the genus has evolved to live in vertebrate hosts. Several recently discovered species appear to have phenotypes that are intermediate between soil bacteria and core Brucella, suggesting that they may represent ancestral traits that were subsequently lost in the traditional species. Remarkably, the broad relationships among Brucella species using a variety of sequence and fragment-based approaches have been upheld when using comparative genomics with whole genomes. Nonetheless, genomes are required for fine-scale resolution of many of the relationships and for understanding the evolutionary history of the genus. We expect that the coming decades will reveal many more hosts and previously unknown diversity in a wide range of environments.

Rhizobium flavescens sp. nov., Isolated from a Chlorothalonil-Contaminated Soil

A Gram-negative, facultative anaerobic, non-lagellated and rod-shaped bacterium FML-4^T was isolated from a chlorothalonil-contaminated soil in Nanjing, China. Phylogenetic analyses of 16S rRNA genes revealed that the strain FML-4^T shared the highest sequence similarity of 97.1% with Ciceribacter thiooxidans KCTC 52231^T, followed by Rhizobium rosettiformans CCM 7583^T (97.0%) and R. daejeonense KCTC 12121^T (96.8%). Although the sequence similarities of the housekeeping genes thrC, rceA, glnII, and atpD between strain FML-4^T and C. thiooxidans KCTC 52231^T were 83.8%, 88.7%, 86.2%, and 92.0%, respectively, strain FML-4^T formed a monophyletic clade in the cluster of Rhizobium species. Importantly, the feature gene of the genus Rhizobium, nifH gene (encoding the dinitrogenase reductase), was detected in strain FML-4^T but not in C. thiooxidans KCTC 52231^T. In addition, strain FML-4^T contained the summed feature 8 (C_18:1ω7c and/or C_18:1ω6c), C_19:0 cyclo ω8c and C_16:0 as the major fatty acids. Genome sequencing of strain FML-4^T revealed a genome size of 7.3 Mbp and a G+C content of 63.0 mol%. Based on the results obtained by phylogenetic and chemotaxonomic analyses, phenotypic characterization, average nucleotide identity (ANI, similarity 77.3-75.4%), and digital DNA-DNA hybridization (dDDH, similarity 24.5-22.3%), it was concluded that strain FML-4^T represented a novel species of the genus Rhizobium, for which the name Rhizobium flavescens sp. nov. was proposed (type strain FML-4^T = CCTCC AB 2019354^T = KCTC 62839^T).

Thalassobius aquimarinus sp. nov., isolated from the Sea of Japan seashore

An aerobic, Gram-negative, non-pigmented non-motile bacterium designed КMM 8518^T was isolated from a seawater sampled from the Sea of Japan seashore. Strain КMM 8518^T grew at 7-42 °C and in the presence of 1-7% NaCl. The phylogenetic analyses based on 16S rRNA gene and whole-genome sequences placed the novel strain КMM 8518^T into the genus Thalassobius as a separate lineage. Strain КMM 8518^T shared the highest 16S rRNA gene sequence similarity of 98% to Thalassobius gelatinovorus KCTC 22092^T and similarity values of ≤ 97% to other recognized Thalassobius species. The average nucleotide identity and digital DNA-DNA hybridization values between strain КMM 8518^T and T. gelatinovorus KCTC 22092^T were 79.6% and 23.5%, respectively. The major respiratory quinone was ubiquinone-10. The major fatty acid was C_18:1ω7c followed by 11-methyl C_18:1ω7c. Polar lipids comprised phosphatidylcholine, phosphatidylglycerol, diphosphatidylglycerol, an unidentified aminolipid, an unidentified phospholipid, and three unidentified lipids. The DNA G+C content of 62.7% was calculated from genome sequence analysis. Based on the phylogenetic analyses and distinctive phenotypic characteristics, the marine bacterium КMM 8518^T is concluded to represent a novel species of the genus Thalassobius for which the name Thalassobius aquimarinus sp. nov. is proposed. The type strain of the species is strain KMM 8518^T (= KCTC 82576^T).

Ruegeria haliotis sp. nov., Isolated from the Gut of the Abalone Haliotis rubra

A Gram-stain-negative, aerobic, non-motile, white-pigmented, short rod-shaped, and alginate-degrading bacterium, designated B1Z28^T, was isolated from the gut of the abalone Haliotis rubra obtained at Weihai, China. Strain B1Z28^T was found to grow at 4-35 °C, pH 6.5-9.0, and in the presence of 0.5-8.0% (w/v) NaCl. Cells were positive for oxidase and catalase activity. The 16S rRNA-based phylogenetic analysis revealed that the nearest phylogenetic neighbors of strain B1Z28^T were Tritonibacter scottomollicae MCCC 1A06440^T (98.1%), Ruegeria faecimaris KCTC 23044^T (98.0%), and Ruegeria meonggei KCTC 32450^T (97.8%). Based on phylogenomic analysis, the average nucleotide identity (ANI) values between strain B1Z28^T and the neighbor strains were 71.6, 77.2, and 78.1%, respectively; the digital DNA-DNA hybridization (dDDH) values based on the draft genomes between strain B1Z28^T and its closest neighbors were 20.5, 20.8, and 21.6%, respectively. Ubiquinone-10 (Q-10) was detected as the predominant respiratory quinone. The dominant cellular fatty acids were Summed feature 8 (contained C_18:1 ω7c and/or C_18:1 ω6c). The polar lipids included phosphatidylethanolamine (PE), diphosphatidylglycerol (DPG), phosphatidylglycerol (PG), phospholipid (PL), aminolipid (AL), and three unidentified lipids. Based on the phylogenetic and phenotypic characteristics, strain B1Z28^T is considered to represent a novel species of the genus Ruegeria, for which the name Ruegeria haliotis sp. nov. is proposed. The type strain is B1Z28^T (= KCTC 72686^T = MCCC 1H00393^T).

Tritonibacter aquimaris sp. nov. and Tritonibacter litoralis sp. nov., two novel members of the Roseobacter group isolated from coastal seawater

Two Gram-stain-negative bacterial strains, SM1969^T and SM1979^T, were isolated from coastal surface seawater of Qingdao, China. They were taxonomically characterized by the phylogenetic, genomic, chemotaxonomic and phenotypic analyses. The two strains shared 97.0% 16S rRNA gene sequence similarity with each other and the highest similarity (96.8-97.5%) with type strains of six species in the genera Shimia, Tritonibacter and Tropicibacter in the Roseobacter group of the family Rhodobacteraceae. In the phylogenetic tree based on single-copy orthologous clusters (OCs), both strains clustered with known species of the genus Tritonibacter and together formed a separate branch adjacent to Tritonibacter ulvae. Although sharing many chemotaxonomic and phenotypic characteristics, the two strains could be differentiated from each other and closely related species by numerous traits. Particularly, strain SM1969^T was found to have a DMSP lyase coding gene dddW in its genome and have the ability to produce DMS from DMSP while strain SM1979^T was not. The average nucleotide identity and in silico DNA-DNA hybridization values between strains SM1969^T and SM1979^T and type strains of closely related species were all below the thresholds to discriminate bacterial species, demonstrating that they constitute two new species in the genus Tritonibacter. The names Tritonibacter aquimaris sp. nov. and Tritonibacter litoralis sp. nov. are proposed for the two new species, with type strains being SM1969^T (= MCCC 1K04320^T = KCTC 72843^T) and SM1979^T (= MCCC 1K04321^T = KCTC 72842^T), respectively.

Comparative genomic analysis of the genus Novosphingobium and the description of two novel species Novosphingobium aerophilum sp. nov. and Novosphingobium jiangmenense sp. nov

Members of the genus Novosphingobium are well known for their metabolically versatile and great application potential in pollution elimination. The three novel bacterial strains, designated 4Y4^T, 4Y9, and 1Y9A^T, were isolated from aquaculture water and characterized by using a polyphasic taxonomic approach. The 16S rRNA gene sequences phylogenetic analysis revealed that the three strains belonged to the genus Novosphingobium. The phylogenomic analysis indicated that the three strains formed two independent and robust branches distinct from all reference strains. The analyses of dDDH values and ANIs between the three strains and their relatives further demonstrated that the three strains represented two different novel genospecies. Comparative genomic analysis of the three isolates and 32 type strains of the genus Novosphingobium showed that the most important central metabolic pathways of these strains appeared to be similar, while specific and specialized metabolic pathways were flexible and variable among these strains. Chemotaxonomic characterization exhibited that the predominant cellular fatty acids were summed feature 8, summed feature 3, and C_14:0 2OH; the major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidyldimethylethanolamine, phosphatidylglycerol, and sphingoglycolipid; the major respiratory quinone and polyamine were Q-10 and spermidine. The DNA G + C contents were 67.6 and 64.7 %. Based on the genotypic and phenotypic characteristics, strains 4Y4^T and 1Y9A^T are concluded to represent two novel species of the genus Novosphingobium, for which the names Novosphingobium aerophilum sp. nov. (type strain 4Y4^T = GDMCC 1.1828 ^T = KACC 21946 ^T) and Novosphingobium jiangmenense sp. nov. (type strain 1Y9A^T = GDMCC 1.1936 ^T = KACC 22085 ^T) are proposed.

Phylogenomic analysis and characterization of carbon monoxide utilization genes in the family Phyllobacteriaceae with reclassification of Aminobacter carboxidus (Meyer et al. 1993, Hördt et al. 2020) as Aminobacter lissarensis comb. nov. (McDonald et al. 2005)

The monotypic carboxydophilic genus Carbophilus has recently been transferred to the genus Aminobacter within the family Phyllobacteriaceae, and Carbophilus carboxidus was renamed Aminobacter carboxidus (comb. nov.) [Hördt et al. 2020]. Due to the poor resolution of the 16S rRNA gene-based phylogeny, an extensive phylogenomic analysis of the family Phyllobacteriaceae was conducted, with particular focus on the genus Aminobacter. Whole genome-based analyses of Phyllobacteriaceae type strains provided evidenced that the genus Aminobacter forms a monophyletic cluster, clearly demarcated from all other members of the family. Close relatedness between A. carboxidus DSM 1086^T and A. lissarensis DSM 17454^T was inferred from core proteome phylogeny, shared gene content, and multilocus sequence analyses. ANI and GGDC provided genetic similarity values above the species demarcating threshold for these two type strains. Metabolic profiling and cell morphology analysis corroborated the phenotypic identity between A. carboxidus DSM 1086^T and A. lissarensis DSM 17454^T. Search for the presence of carbon monoxide dehydrogenase (CODH) genes in Phyllobacteriaceae genomes revealed that the form II CODH is widespread in the family, whereas form I CODH was detected in few Mesorhizobium type strains, and in both A. carboxidus DSM 1086^T and A. lissarensis DSM 17454^T. Results of phylogenomic, chemotaxonomic, and morphological investigations, combined with the presence of similarly arranged CODH genes, indicate that A. carboxidus DSM 1086^T and A. lissarensis DSM 17454^T are distinct strains of the same species. Hence A. carboxidus is a later subjective heterotypic synonym of A. lissarensis.

Genomic Metrics Applied to Rhizobiales (Hyphomicrobiales): Species Reclassification, Identification of Unauthentic Genomes and False Type Strains

Taxonomic decisions within the order Rhizobiales have relied heavily on the interpretations of highly conserved 16S rRNA sequences and DNA–DNA hybridizations (DDH). Currently, bacterial species are defined as including strains that present 95–96% of average nucleotide identity (ANI) and 70% of digital DDH (dDDH). Thus, ANI values from 520 genome sequences of type strains from species of Rhizobiales order were computed. From the resulting 270,400 comparisons, a ≥95% cut-off was used to extract high identity genome clusters through enumerating maximal cliques. Coupling this graph-based approach with dDDH from clusters of interest, it was found that: (i) there are synonymy between Aminobacter lissarensis and Aminobacter carboxidus, Aurantimonas manganoxydans and Aurantimonas coralicida, “Bartonella mastomydis,” and Bartonella elizabethae, Chelativorans oligotrophicus, and Chelativorans multitrophicus, Rhizobium azibense, and Rhizobium gallicum, Rhizobium fabae, and Rhizobium pisi, and Rhodoplanes piscinae and Rhodoplanes serenus; (ii) Chelatobacter heintzii is not a synonym of Aminobacter aminovorans; (iii) “Bartonella vinsonii” subsp. arupensis and “B. vinsonii” subsp. berkhoffii represent members of different species; (iv) the genome accessions GCF_003024615.1 (“Mesorhizobium loti LMG 6125^T”), GCF_003024595.1 (“Mesorhizobium plurifarium LMG 11892^T”), GCF_003096615.1 (“Methylobacterium organophilum DSM 760^T”), and GCF_000373025.1 (“R. gallicum R-602 sp^T”) are not from the genuine type strains used for the respective species descriptions; and v) “Xanthobacter autotrophicus” Py2 and “Aminobacter aminovorans” KCTC 2477^T represent cases of misuse of the term “type strain”. Aminobacter heintzii comb. nov. and the reclassification of Aminobacter ciceronei as A. heintzii is also proposed. To facilitate the downstream analysis of large ANI matrices, we introduce here ProKlust (“Prokaryotic Clusters”), an R package that uses a graph-based approach to obtain, filter, and visualize clusters on identity/similarity matrices, with settable cut-off points and the possibility of multiple matrices entries.

Fertoeibacter niger gen. nov., sp. nov. a novel alkaliphilic bacterium of the family Rhodobacteraceae

Three Gram-stain-negative, non-motile, oxidase- and catalase-positive, rod-shaped, black, facultative phototrophic bacterial strains, RG-N-1a^T, DMA-N-7a and RA-N-9 were isolated from the water sample from Lake Fertő/Neusiedler See (Hungary). Phylogenetic analysis based on the 16S rRNA gene sequences revealed that the strains form a distinct linage within the family Rhodobacteraceae and their closest relatives are Tabrizicola piscis K13M18^T (96.32%) followed by Cypionkella psychrotolerans PAMC 27389^T (96.25%). The novel bacterial strains prefer alkaline environments and grow optimally at 23-33 °C in the presence of NaCl (1-2 w/v%). Bacteriochlorophyll a was detected. Cells contained exclusively ubiquinone Q-10. The major cellular fatty acids were C_{18 : 1}ω7c, C_{19 : 1}iso ω5c, C_{18 : 0} 3-OH and C_{18 : 1}ω7c 11-methyl. The polar lipid profile contains diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, an unidentified phospholipid and four unidentified lipids. The assembled draft genome of RG-N-1a^T had 33 contigs with N50 values 315 027 nt, 96× genome coverage, total length of 4 326 551 bp and a DNA G+C content of 64.9%. Genome-based calculations (genome-to-genome distance and DNA G+C percentage) and pairwise amino acid identity (AAI <73.5%) indicate that RG-N-1a^T represents a novel genus. RG-N-1a^T (=DSM 108317^T=NCAIM B.02647^T) is suggested as the type strain of a novel genus and species in the family Rhodobacteraceae, for which the name Fertoeibacter niger gen. nov., sp. nov. is proposed.

Roseibium litorale sp. nov., isolated from a tidal flat sediment and proposal for the reclassification of Labrenzia polysiphoniae as Roseibium polysiphoniae comb. nov

A novel Gram-stain-negative, facultatively anaerobic, rod-shaped and non-motile bacterial strain, designated as 4C16A^T, was isolated from a tidal flat sediment and characterized by using a polyphasic taxonomic approach. Strain 4C16A^T was found to grow at 10-40 °C (optimum, 28 °C), at pH 5.0-10.0 (optimum, pH 6.0-7.0) and in 0-6 % (w/v) NaCl (optimum, 1 %). Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain 4C16A^T fell into the genus Roseibium, and shared the highest identity of 98.9 % with the closest type strain Roseibium suaedae KACC 13772^T and less than 98.0 % identity with other type strains of recognized species within this genus. The phylogenomic analysis indicated that strain 4C16A^T formed an independent branch within this genus. The 28.6 % digital DNA-DNA hybridization estimate and 85.0 % average nucleotide identity between strains 4C16A^T and R. suaedae KACC 13772^T were the highest, but still far below their respective threshold for species definition, implying that strain 4C16A^T should represent a novel genospecies. The predominant cellular fatty acid was summed feature 8; the polar lipids were diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylmonomethylethanolamine; the respiratory quinones were Q-9 and Q-10. The genomic DNA G+C content was 59.8mol %. Based on phylogenetic analyses and phenotypic and chemotaxonomic characteristics, strain 4C16A^T is concluded to represent a novel species of the genus Roseibium, for which the name Roseibium litorale sp. nov. is proposed. The type strain of the species is 4C16A^T (=GDMCC 1.1932^T=KACC 22078^T). We also propose the reclassification of Labrenzia polysiphoniae as Roseibium polysiphoniae comb. nov. and 'Labrenzia callyspongiae' as Roseibium callyspongiae sp. nov.

Filling the Gaps in the Cyanobacterial Tree of Life-Metagenome Analysis of Stigonema ocellatum DSM 106950, Chlorogloea purpurea SAG 13.99 and Gomphosphaeria aponina DSM 107014

Cyanobacteria represent one of the most important and diverse lineages of prokaryotes with an unparalleled morphological diversity ranging from unicellular cocci and characteristic colony-formers to multicellular filamentous strains with different cell types. Sequencing of more than 1200 available reference genomes was mainly driven by their ecological relevance (Prochlorococcus, Synechococcus), toxicity (Microcystis) and the availability of axenic strains. In the current study three slowly growing non-axenic cyanobacteria with a distant phylogenetic positioning were selected for metagenome sequencing in order to (i) investigate their genomes and to (ii) uncover the diversity of associated heterotrophs. High-throughput Illumina sequencing, metagenomic assembly and binning allowed us to establish nearly complete high-quality draft genomes of all three cyanobacteria and to determine their phylogenetic position. The cyanosphere of the limnic isolates comprises up to 40 heterotrophic bacteria that likely coexisted for several decades, and it is dominated by Alphaproteobacteria and Bacteriodetes. The diagnostic marker protein RpoB ensured in combination with our novel taxonomic assessment via BLASTN-dependent text-mining a reliable classification of the metagenome assembled genomes (MAGs). The detection of one new family and more than a dozen genera of uncultivated heterotrophic bacteria illustrates that non-axenic cyanobacteria are treasure troves of hidden microbial diversity.

Qingshengfaniella alkalisoli gen. nov., sp. nov., a p-hydroxybenzoate-degrading strain isolated from saline soil

p-Hydroxybenzoate is an allelopathic compound commonly found in soil from long-term monoculture cropping systems. During the bacterial diversity analysis of saline soil, a Gram-negative, non-spore forming, non-motile, aerobic p-hydroxybenzoate-degrading bacterial strain, designated LN3S51^T, was isolated from saline soil which was sampled from Tumd Right Banner, Inner Mongolia, northern China. Strain LN3S51^T grew at 4-40 °C (optimum, 30 °C), pH 5.0-10.0 (optimum, pH 7.0) and 0-15 % NaCl (optimum 3.0 %). Though strain LN3S51^T has the highest 16S rRNA gene similarities to Litoreibacter ponti GJSW-31^T (96.0 %), the phylogenetic tree based on the 16S rRNA gene sequences showed that it clustered with Fluviibacterium aquatile SM1902^T (95.8 %), Meridianimarinicoccus roseus TG-679^T (93.9 %), and Phycocomes zhengii LMIT002^T (93.9 %). Strain LN3S51^T contained Q-10 as the major ubiquinone. Phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylcholine (PC), diphosphatidylglycerol (DPG), an unidentified aminolipid (AL), and two unidentified lipids (L) were the major polar lipids. The major fatty acids were sum feature 8 (C_18 : 1  ω7c and/or C_18 : 1  ω6c), C_16 : 0, C_18 : 0, and C_18 : 1  ω7c 11-methyl. The genome of strain LN3S51^T consisted of a 2 257 066 bp chromosome and four plasmids with a 59.1 mol% of genomic DNA G+C content. The average nucleotide identity (ANI) and digital DNA-DNA hybridization score (dDDH) values of strain LN3S51^T to F. aquatile SM1902^T, M. roseus TG-679^T, P. zhengii LMIT002^T, and L. ponti GJSW-31^T were 69.6, 70.9, 70.6, and 69.5 %, and 20.0, 19.5, 19.0, and 20.0 %, respectively. Based on the results of phylogenetic, chemtaxonomic and phenotypic characterization, strain LN3S51^T is considered to represent a novel species in a new genus within the family Rhodobacteraceae, for which Qingshengfaniella alkalisoli gen. nov., sp. nov. is proposed. The type strain is LN3S51^T (=CGMCC 1.17099^T=KCTC 72457^T).

A Novel Moderately Thermophilic Facultative Methylotroph within the Class Alphaproteobacteria

Methylotrophic bacteria (non-methanotrophic methanol oxidizers) consuming reduced carbon compounds containing no carbon–carbon bonds as their sole carbon and energy source have been found in a great variety of environments. Here, we report a unique moderately thermophilic methanol-oxidising bacterium (strain LS7-MT) that grows optimally at 55 °C (with a growth range spanning 30 to 60 °C). The pure isolate was recovered from a methane-utilizing mixed culture enrichment from an alkaline thermal spring in the Ethiopia Rift Valley, and utilized methanol, methylamine, glucose and a variety of multi-carbon compounds. Phylogenetic analysis of the 16S rRNA gene sequences demonstrated that strain LS7-MT represented a new facultatively methylotrophic bacterium within the order Hyphomicrobiales of the class Alphaproteobacteria. This new strain showed 94 to 96% 16S rRNA gene identity to the two methylotroph genera, Methyloceanibacter and Methyloligella. Analysis of the draft genome of strain LS7-MT revealed genes for methanol dehydrogenase, essential for methanol oxidation. Functional and comparative genomics of this new isolate revealed genomic and physiological divergence from extant methylotrophs. Strain LS7-MT contained a complete mxaF gene cluster and xoxF1 encoding the lanthanide-dependent methanol dehydrogenase (XoxF). This is the first report of methanol oxidation at 55 °C by a moderately thermophilic bacterium within the class Alphaproteobacteria. These findings expand our knowledge of methylotrophy by the phylum Proteobacteria in thermal ecosystems and their contribution to global carbon and nitrogen cycles.

Thermaurantiacus tibetensis gen. nov., sp. nov., a novel moderately thermophilic bacterium isolated from hot spring microbial mat in Tibet

Two bacterial strains SYSU G02173^T and SYSU G03142 were isolated from hot springs in Tibet, China. Based on the results of nearly full-length 16S rRNA gene sequences and phylogenetic analyses, strains SYSU G02173^T and SYSU G03142 were assigned to the family Sphingosinicellaceae, and were closest to Sandaracinobacter sibiricus RB16-17 ^T (96.04% and 96.12% similarity, respectively). Cells of the both new strains were observed to be motile rod-shape, Gram-staining negative. Growth occurred at pH 6-8 (optimal: pH 7.0) and 37-55 °C (optimal: 45 °C) with 0-1.0% (w/v) NaCl in T4 broth. The cells were found to be positive for oxidase and catalase activities. The major respiratory ubiquinone was Q-8. The major fatty acids were identified as summed feature 8 (C_18:1 ω7c and/or C_18:1 ω6c), C_16:0, C_14:0 2-OH. The major polar lipids were found to consist of sphingoglycolipid, phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, one unidentified phospholipid, one unidentified glycolipid, three unidentified aminolipids and two unidentified polar lipids. The DNA G + C contents of strains SYSU G02173^T and SYSU G03142 were 71.8%. The average nucleotide identity (ANI) value between strain SYSU G02173^T and SYSU G03142 was 99.98%. The amino acid identity (AAI) values between them and their closely related species were below 66.14%. The isolates are characterized by aerobic growth, a yellow endocellular pigment and a higher optimum growth temperature. The results showed that strains SYSU G02173^T and SYSU G03142 represent a novel species of a novel genus in the family Sphingomonadaceae, and thus the name Thermaurantiacus tibetensis (type strain SYSU G02173^T = KCTC 72052 ^T = CGMCC 1.16680 ^T) is proposed.

Pseudorhodobacter turbinis sp. nov., isolated from the gut of the Korean turban shell, Turbo cornutus

A novel Gram-stain-negative, coccus-shaped, aerobic and motile bacterial strain, designated S12M18^T, was isolated from the gut of the Korean turban shell, Turbo cornutus. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain S12M18^T belonged to the genus Pseudorhodobacter and had the highest 16S rRNA gene sequence similarity twith Pseudorhodobacter aquimaris HDW-19^T (98.63 %). The phylogenomic tree congruently verified that strain S12M18^T occupies a taxonomic position within the genus Pseudorhodobacter. The OrthoANIu value between strain S12M18^T and P. aquimaris HDW-19^T was 87.22 %. The major cellular fatty acid of strain S12M18^T was summed feature 8 (C_18 : 1 ω7c or C_18 : 1 ω6c). The major components of the polar lipids were phosphatidylcholine, phosphatidylglycerol and phosphatidylethanolamine. The predominant isoprenoid quinone was Q-10. The DNA G＋C content was 57.8 mol%. The polyphasic analyses indicated that strain S12M18^T represents a novel species of the genus Pseudorhodobacter, for which the name Pseudorhodobacter turbinis sp. nov. is proposed. The type strain is S12M18^T (=KCTC 62742^T=JCM 33168^T).

Entomobacter blattae gen. nov., sp. nov., a new member of the Acetobacteraceae isolated from the gut of the cockroach Gromphadorhina portentosa

A novel bacterium designated G55GP^T and pertaining to the family Acetobacteraceae was isolated from the gut of the Madagascar hissing cockroach Gromphadorhina portentosa. The Gram-negative cells were rod-shaped and non-motile. The complete 16S rRNA sequence of the strain G55GP^T showed the highest pairwise similarity to Gluconacetobacter johannae CFN-Cf-55T (95.35 %), suggesting it represents a potential new genus of the family Acetobacteraceae. Phylogenetic analysis based on 16S rRNA gene and 106 orthologous housekeeping protein sequences revealed that G55GP^T forms a monophyletic clade with the genus Commensalibacter, which thus far has also been isolated exclusively from insects. The G55GP^T genome size was 2.70 Mbp, and the G+C content was 45.4 mol%, which is lower than most acetic acid bacteria (51-68 mol%) but comparable to Swingsia samuiensis AH83^T (45.1 mol%) and higher than Commensalibacter intestini A911^T (36.8 mol%). Overall genome relatedness indices based on gene and protein sequences strongly supported the assignment of G55GP^T to a new genus within the family Acetobacteraceae. The percentage of conserved proteins, which is a useful metric for genus differentiation, was below 54 % when comparing G55GP^T to type strains of acetic acid bacteria, thus strongly supporting our hypothesis that G55GP^T is a member of a yet-undescribed genus. The fatty acid composition of G55GP^T differed from that of closely related acetic acid bacteria, particularly given the presence of C_19 : 1  ω9c/ω11c and the absence of C_14 : 0 and C_14 : 0 2-OH fatty acids. Strain G55GP^T also differed in terms of metabolic features such as its ability to produce acid from d-mannitol, and its inability to produce acetic acid from ethanol or to oxidize glycerol to dihydroxyacetone. Based on the results of combined genomic, phenotypic and phylogenetic characterizations, isolate G55GP^T (=LMG 31394^T=DSM 111244^T) is considered to represent a new species in a new genus, for which we propose the name Entomobacter blattae gen. nov., sp. nov.

Recent development and new insight of diversification and symbiosis specificity of legume rhizobia: mechanism and application

Currently, symbiotic rhizobia (sl., rhizobium) refer to the soil bacteria in α- and β-Proteobacteria that can induce root and/or stem nodules on some legumes and a few of nonlegumes. In the nodules, rhizobia convert the inert dinitrogen gas (N₂ ) into ammonia (NH₃ ) and supply them as nitrogen nutrient to the host plant. In general, this symbiotic association presents specificity between rhizobial and leguminous species, and most of the rhizobia use lipochitooligosaccharides, so called Nod factor (NF), for cooperating with their host plant to initiate the formation of nodule primordium and to inhibit the plant immunity. Besides NF, effectors secreted by type III secretion system (T3SS), exopolysaccharides and many microbe-associated molecular patterns in the rhizobia also play important roles in nodulation and immunity response between rhizobia and legumes. However, the promiscuous hosts like Glycine max and Sophora flavescens can nodulate with various rhizobial species harbouring diverse symbiosis genes in different soils, meaning that the nodulation specificity/efficiency might be mainly determined by the host plants and regulated by the soil conditions in a certain cases. Based on previous studies on rhizobial application, we propose a '1+n-N' model to promote the function of symbiotic nitrogen fixation (SNF) in agricultural practice, where '1' refers to appreciate rhizobium; '+n' means the addition of multiple trace elements and PGPR bacteria; and '-N' implies the reduction of chemical nitrogen fertilizer. Finally, open questions in the SNF field are raised to future think deeply and researches.

Defining the Rhizobium leguminosarum Species Complex

Bacteria currently included in Rhizobium leguminosarum are too diverse to be considered a single species, so we can refer to this as a species complex (the Rlc). We have found 429 publicly available genome sequences that fall within the Rlc and these show that the Rlc is a distinct entity, well separated from other species in the genus. Its sister taxon is R. anhuiense. We constructed a phylogeny based on concatenated sequences of 120 universal (core) genes, and calculated pairwise average nucleotide identity (ANI) between all genomes. From these analyses, we concluded that the Rlc includes 18 distinct genospecies, plus 7 unique strains that are not placed in these genospecies. Each genospecies is separated by a distinct gap in ANI values, usually at approximately 96% ANI, implying that it is a 'natural' unit. Five of the genospecies include the type strains of named species: R. laguerreae, R. sophorae, R. ruizarguesonis, "R. indicum" and R. leguminosarum itself. The 16S ribosomal RNA sequence is remarkably diverse within the Rlc, but does not distinguish the genospecies. Partial sequences of housekeeping genes, which have frequently been used to characterize isolate collections, can mostly be assigned unambiguously to a genospecies, but alleles within a genospecies do not always form a clade, so single genes are not a reliable guide to the true phylogeny of the strains. We conclude that access to a large number of genome sequences is a powerful tool for characterizing the diversity of bacteria, and that taxonomic conclusions should be based on all available genome sequences, not just those of type strains.

Tabrizicola oligotrophica sp. nov. and Rhodobacter tardus sp. nov., two new species of bacteria belonging to the family Rhodobacteraceae

Two Gram-stain-negative, aerobic, non-motile bacteria, designated KMS-5^T and CYK-10^T, were isolated from freshwater environments. 16S rRNA gene sequence similarity results indicated that these two novel strains belong to the family Rhodobacteraceae. Strain KMS-5^T is closely related to species within the genus Tabrizicola (96.1-96.8 % sequence similarity) and Cypionkella (96.5-97.0 %). Strain CYK-10^T is closest to Rhodobacter thermarum YIM 73036^T with 96.6 % sequence similarity. Phylogenetic analyses based on 16S rRNA gene sequences and an up-to-date bacterial core gene set showed that strain KMS-5^T is affiliated with species in the genus Tabrizicola and strain CYK-10^T is placed in a distinct clade with Rhodobacter blasticus ATCC 33485^T, Rhodobacter thermarum YIM 73036^T and Rhodobacter flagellatus SYSU G03088^T. These two strains shared common chemotaxonomic features comprising Q-10 as the major quinone, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylcholine as the principal polar lipids, and C_18 : 1  ω7c as the main fatty acid. The average nucleotide identity, average amino acid identity and digital DNA-DNA hybridization values between these two novel isolates and their closest relatives were below the cut-off values of 95-96, 90 and 70 %, respectively, used for species demarcation. The obtained polyphasic taxonomic data suggested that strain KMS-5^T represents a novel species within the genus Tabrizicola, for which the name Tabrizicola oligotrophica sp. nov. is proposed with KMS-5^T (=BCRC 81196^T=LMG 31337^T) as the type strain, and strain CYK-10^T should represent a novel species of the genus Rhodobacter, for which the name Rhodobacter tardus sp. nov. is proposed with CYK-10^T (=BCRC 81191^T=LMG 31336^T) as the type strain.

Propylenella binzhouense gen. nov., sp. nov. isolated from activated sludge, and proposal of Propylenellaceae fam. nov

A Gram-stain-negative, non-spore-forming, non-motile, short-rod-shaped, and aerobic bacterial strain (designated L72^T) was isolated from propylene oxide saponification wastewater activated sludge obtained from a wastewater treatment facility in Binzhou (Shandong Province, PR China). Strain L72^T grew between 25 and 40 °C (optimum growth at 30 °C). The pH range for growth was between 6.0 and 8.0 (optimum growth at pH 7.0). The range of NaCl concentrations for the growth of strain L72^T was 0-3.0 % (w/v), with optimum growth at 1.0-2.0 % (w/v). The major cellular fatty acids of strain L72^T were C_19:0cyclo ω8c, C_18:1ω7c, iso-C_15:0, and anteiso-C_15:0. Strain L72^T contained Q-10 as the predominant respiratory quinone. The polar lipid profile was composed of Phosphatidylcholine, Glycolipid, Aminophospholipid, Phosphatidylethanolamine, Phosphatidylserine, Phosphatidyldimethylethanolamine, one unknown lipid (L) and two unidentified Phospholipids (PL). Genome sequencing revealed a genome size of 4,703,686 bp and a G + C content of 69.0 mol%. The 16S rRNA gene sequence similarities of strain L72^T with other species were less than 94%. Phylogenetic analyses based on 16S rRNA gene sequences and genome data, revealed that strain L72^T formed a distinct phylogenetic lineage within the order Hyphomicrobiales, separating them from members of all families. Strain L72^T showed 70.7% average nucleotide identity and 18.6% digital DNA-DNA hybridization identity with the closely related species Rhodoligotrophos defluvii. Based on the phenotypic, phylogenetic and chemotaxonomic data, a new family Propylenellaceae fam. nov. comprising the genus Propylenella gen. nov. and species Propylenella binzhouense sp. nov. is proposed. The type strain is L72^T (=  CCTCC AB 2019081^T  =  KCTC 72254^T).

Hongsoonwoonella zoysiae gen. nov., sp. nov., a new member of the family Stappiaceae isolated from a tidal mudflat

A Gram stain-negative bacterial strain, designated SY4-7^T, was isolated from rhizosphere mudflat of a halophyte (Zoysia sinica) collected around Seonyu Island, Republic of Korea. Cells of the organism were strictly aerobic, non-sporulating, non-motile rods and grew at 20-42 °C, pH 6-8 and 1-6% (w/v) NaCl. The 16S rRNA gene-based phylogenetic analyses revealed that strain SY4-7^T formed an independent cluster separated from the recognized genera of the family Stappiaceae, which was also supported by phylogenomic analysis-based 92-core gene sequences. The type stains of the phylogenetically closest relatives were Stappia indica (95.6% sequence similarity), Stappia stellulata (95.1%) and Roseibium hamelinense (95.1%). The isoprenoid quinone was Q-10. The polar lipids consisted of phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, three unidentified aminophospholipids, an unidentified phosphoglycolipid, an unidentified aminolipid, two unidentified phospholipids and an unidentified lipid. The major cellular fatty acids are C_18:1ω7c and C_19:1 cyclo ω8c. The G + C content of the genomic DNA is 60.7%. Discrimination of the organism from all the recognized genera of the family Stappiaceae was apparent by the chemotaxonomic and phylogenetic features. Based on the results presented here, strain SY4-7^T (= KCTC 72226^T = NBRC 113902^T) represents a novel species of a new genus in the family Stappiaceae, for which the name Hongsoonwoonella zoysiae sp. nov. is proposed.

Alkalicaulis satelles gen. nov., sp. nov., a novel haloalkaliphile isolated from a laboratory culture cyanobacterium Geitlerinema species and proposals of Maricaulaceae fam. nov., Robiginitomaculaceae fam. nov., Maricaulales ord. nov. and Hyphomonadales ord. nov

A prosthecate bacterial strain, designated G-192^T, was isolated from decaying biomass of a haloalkaliphilic cyanobacterium Geitlerinema sp. Z-T0701. The cells were aerobic, Gram-negative, non-endospore-forming and dimorphic, occurring either as sessile bacteria with a characteristic stalk or as motile flagellated cells. The strain utilized a limited range of substrates, mostly peptonaceous, but was able to degrade whole proteins. Growth occurred at 5-46 °C (optimum, 35-40 °C), pH 7.3-10.3 (optimum, pH 8.0-9.0), 0-14 % NaCl (v/w; optimum, 2.0-6.0 %, v/w). The G+C content of the genomic DNA of strain G-192^T was 66.8%. Phylogenetic analysis of the 16S rRNA gene sequence revealed that strain G-192^T formed a distinct evolutionary lineage within the family Hyphomonadaceae. Strain G-192^T showed the highest 16S rRNA sequence similarity to Glycocaulis profundi ZYF765^T (95.2%), Oceanicaulis stylophorae GISW-4^T (94.2%) and Marinicauda salina WD6-1^T (95.5%). The major cellular fatty acids (>5% of the total) were C_18:1 ω9c, C_18:0 and 11-methyl-C_18:1 ω7c. The major polar lipids were glycolipids and phospholipids. The only respiratory quinone was ubiquinone-10 (Q-10). Based on polyphasic results including phylogenomic data, the novel strain could be distinguished from other genera, which suggests that strain G-192^T represents a novel species of a new genus, for which the name Alkalicaulis satelles gen. nov., sp. nov. is proposed. The type strain is G-192^T (=VKM B-3306^T=KCTC 72746^T). The strain is the first representative of the stalked bacteria associated with a haloalkaliphilic cyanobacterium. Based on phylogenomic indices and phenotypic data, it is proposed to evolve two novel families Maricaulaceae fam. nov. and Robiginitomaculaceae fam. nov. out of the current family Hyphomonadaceae. In addition, it is proposed to place the first two families in the novel order Maricaulales ord. nov. and novel order Hyphomonadales ord. nov. is proposed to accommodate the family Hyphomonadaceae.

Phylogenomics reveals the basis of adaptation of Pseudorhizobium species to extreme environments and supports a taxonomic revision of the genus

The family Rhizobiaceae includes many genera of soil bacteria, often isolated for their association with plants. Herein, we investigate the genomic diversity of a group of Rhizobium species and unclassified strains isolated from atypical environments, including seawater, rock matrix or polluted soil. Based on whole-genome similarity and core genome phylogeny, we show that this group corresponds to the genus Pseudorhizobium. We thus reclassify Rhizobium halotolerans, R. marinum, R. flavum and R. endolithicum as P. halotolerans sp. nov., P. marinum comb. nov., P. flavum comb. nov. and P. endolithicum comb. nov., respectively, and show that P. pelagicum is a synonym of P. marinum. We also delineate a new chemolithoautotroph species, P. banfieldiae sp. nov., whose type strain is NT-26^T (=DSM 106348^T=CFBP 8663^T). This genome-based classification was supported by a chemotaxonomic comparison, with increasing taxonomic resolution provided by fatty acid, protein and metabolic profiles. In addition, we used a phylogenetic approach to infer scenarios of duplication, horizontal transfer and loss for all genes in the Pseudorhizobium pangenome. We thus identify the key functions associated with the diversification of each species and higher clades, shedding light on the mechanisms of adaptation to their respective ecological niches. Respiratory proteins acquired at the origin of Pseudorhizobium were combined with clade-specific genes to enable different strategies for detoxification and nutrition in harsh, nutrient-poor environments.

Donghicola mangrovi sp. nov., a member of the family Rhodobacteraceae isolated from mangrove forest in Thailand

Two novel Gram-stain-negative, rod-shaped and non-motile bacterial strains, designated B5-SW-15^T and C2-DW-16, were isolated from water collected in mangrove forests in Ranong Province, Thailand. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strains B5-SW-15^T and C2-DW-16 belonged to the genus Donghicola and were most closely related to Donghicola tyrosinivorans DSM 100212^T (98.2 and 98.1 %, respectively) and Donghicola eburneus DSM 29127^T (97.7 and 97.6 %, respectively). The average nucleotide identity and digital DNA-DNA hybridization values between strain B5-SW-15^T, strain C2-DW-16 and related species were 95.8 and 71.6 % (to strain C2-DW-16), 76.8 and 21.3 % (to D. tyrosinivorans DSM 100212^T) and 80.3 and 24.2 % (to D. eburneus DSM 29127^T), respectively. The predominant cellular fatty acids (>5 %) were summed feature 8 (C_18 : 1  ω6c and/or C_18 : 1  ω7c), C_16 : 0 and C_12 : 1 3-OH. Ubiquinone Q-10 was the sole respiratory quinone. DNA G+C contents of the isolates were 61.0 and 61.2 mol% based on whole genome sequences. Strains B5-SW-15^T and C2-DW-16 contained aminolipid, phosphatidylcholine, phosphatidylethanolamine and phosphatidylglycerol as the major polar lipids. On the basis of the results from phenotypic, chemotaxonomic and phylogenetic analyses, strains B5-SW-15^T and C2-DW-16 constitute a novel species of the genus Donghicola in the family Rhodobacteraceae for which the name Donghicola mangrovi sp. nov. is proposed. The type strain is B5-SW-15^T (=BCC 56522^T=TBRC 9562^T=KCTC 72743^T).

Sphaerochaeta halotolerans sp. nov., a novel spherical halotolerant spirochete from a Russian heavy oil reservoir, emended description of the genus Sphaerochaeta, reclassification of Sphaerochaeta coccoides to a new genus Parasphaerochaeta gen. nov. as Parasphaerochaeta coccoides comb. nov. and proposal of Sphaerochaetaceae fam. nov

Anaerobic, fermentative, halotolerant bacteria, strains 4-11^T and 585, were isolated from production water of two low-temperature petroleum reservoirs (Russia) and were characterized by using a polyphasic approach. Cells of the strains were spherical, non-motile and 0.30-2.5 µm in diameter. Strain 4-11^T grew optimally at 35 °C, pH 6.0 and 1.0-2.0% (w/v) NaCl. Both strains grew chemoorganotrophically with mono-, di- and trisaccharides. The major cellular fatty acids of both strains were C_14:0, C_16:0, C_16:1 ω9 and C_18:0 3-OH. Major polar lipids were glycolipids and phospholipids. The 16S rRNA gene sequences of the strains 4-11^T and 585 had 99.9% similarity and were most closely related to the sequence of Sphaerochaeta associata GLS2^T (96.9, and 97.0% similarity, respectively). The G+C content of the genomic DNA of strains 4-11^T and 585 were 46.8 and 46.9%, respectively. The average nucleotide identity and digital DNA-DNA hybridization values between the genomes of strain 4-11^T and S. associata GLS2^T were 73.0 and 16.9%, respectively. Results of phylogenomic metrics analysis of the genomes and 120 core proteins of strains 4-11^T and 585 and their physiological and biochemical characteristics confirmed that the strains represented a novel species of the genus Sphaerochaeta, for which the name Sphaerochaeta halotolerans sp. nov. is proposed, with the type strain 4-11^T (=VKM B-3269^T=KCTC 15833^T). Based on the results of phylogenetic analysis, Sphaerochaeta coccoides was reclassified as member of a new genus Parasphaerochaeta gen. nov., Parasphaerochaeta coccoides comb. nov. The genera Sphaerochaeta and Parasphaerochaeta form a separate clade, for which a novel family, Sphaerochaetaceae fam. nov., is proposed.