The current understanding of human gut microbial community is mainly limited to taxonomic features at the genus level. Here, we examined the human gut microbial community at the species level by metataxonomics. To achieve this purpose, a high-throughput approach involving operational phylogenetic unit analysis of the near full-length 16S ribosomal RNA (rRNA) gene sequence was used. A total of 1,235 species-level phylotypes (SLPs) were classified in the feces of 120 Chinese healthy individuals, including 461 previously classified species, 358 potentially new species, and 416 potentially new taxa, which were categorized into low, medium, and high prevalent bacteria groups based on their prevalence. Each individual harbored 186 ± 51 SLPs on average. There was no universal bacterial species shared by all the individuals. However, 90 ± 19 of 116 SLPs were shared in the high prevalent bacteria group. Thirty-two out of thirty-eight species in the high prevalent bacteria group detected in this study were also found in at least one previous study on human gut microbiota based on either culture-dependent or culture-independent approaches. Through compositional analysis, a hierarchical clustering of the prevalence and relative abundance of the 1,235 SLPs revealed two types of gut microbial communities, which were dominated by Prevotella copri and Bacteroides vulgatus, respectively. The type dominated by P. copri was more prevalent in northern China, while the B. vulgatus-dominant type was more prevalent in southern China. Therefore, P-and B-type gut microbial communities in China were proposed. It was found that 166 out of 461 known bacterial species have been previously reported as potential pathogens, and the individuals sampled for this study harbored 20 of these potential pathogenic species on average. The top two most abundant and prevalent potential pathogenic species were Klebsiella pneumoniae and Bacteroides fragilis.

Four novel strains (592T, S592, MF47T and SMF47) were isolated from Tibetan antelopes (Pantholops hodgsonii) and plateau pikas (Ochotona curzoniae), respectively. The cells were aerobic, non-motile, Gram-stain- and catalase-positive, rod-shaped bacteria. The 16S rRNA gene sequences of the four strains showed highest similarities to Aeromicrobium fastidiosum DSM 10552T (98.1, 98.6, 98.7 and 98.7 %, respectively), and the phylogenetic analyses based on 16S rRNA gene and genomic sequences indicated that strains 592T and MF47T represent two novel species. The four isolates produced acid from l-rhamnose, d-xylose and cellobiose, but were unable to reduce nitrate. The DNA G+C contents of strains 592T and MF47T were 70.3 and 69.8 mol%, respectively. The digital DNA–DNA hybridization value between strains 592T and MF47T was 32.6 %, lower than the threshold of 70 %, indicating they belong to different species. The four strains’ genomes displayed less than 24.6 % DNA–DNA relatedness with all available genomes of the genus Aeromicrobium in the NCBI database, including Aeromicrobium fastidiosum NBRC 14897T and Aeromicrobium ginsengisoli JCM 14732T. The major fatty acids of the four strains were C18 : 1  ω9c and C18 : 0 10-methyl, and the main polar lipids were diphosphatidylglycerol, phosphatidylglycerol and phosphatidylinositol. The predominant respiratory quinones were MK-9(H4) and MK-8(H4). The cell-wall peptidoglycan contained ll-diaminopimelic acid. Based on these genotypic, phenotypic and biochemical analyses, it is proposed that the four unidentified bacteria be classified as two novel species, Aeromicrobium chenweiae sp. nov. and Aeromicrobium yanjiei sp. nov. The type strains are 592T (=CGMCC1.16526T=DSM 106289T) and MF47T (=CGMCC 1.17444T=JCM 33790T), respectively.

Four novel strains isolated from the cloacal contents of snow finches (Montifringilla taczanowskii) were characterized as aerobic, Gram-stain-negative, slightly motile, and rod-shaped. Analysis of the 16S rRNA gene sequence revealed that strain CF-458T had the highest similarities of 96.9 and 96.4 % with Limnobaculum parvum HYN0051T and Pragia fontium DSM 5563T, while strain CF-1111T shared the highest similarities of 96.4 and 96.1 % with Pantoea rodasii LMG 26273T and Pectobacterium punjabense SS95T. Phylogenomic analysis showed the four isolates were separated into group Ⅰ (CF-458T and CF-917) and group Ⅱ (CF-1111T and CF-509), and clustered independently in the vicinity of the genera Limnobaculum and Pragia . Summed feature 3 (C16 : 1  ω7c and/or C16 : 1  ω6c, 23.9 and 17.2 %, respectively), C16 : 0 (21.8 and 22.1 %, respectively) and C14 : 0 (10.6 and 17.7 %, respectively) were the common major fatty acids, and summed feature 8 (C18 : 1  ω7c and/or C18 : 1  ω6c, 12.3 %) was also a major fatty acid for strain CF-458T while cyclo-C17 : 0 (13.1%) was for strain CF-1111T. Both had Q-8 as the sole quinone and contained phosphatidylethanolamine, phosphatidylglycerol, and diphosphatidylglycerol as the major polar lipids. The DNA G+C content of strains CF-458T and CF-1111T was 45.7 and 45.4 mol%, respectively. Based on taxonomic position in the phylogenomic tree and phenotypic properties, two novel species of a new genus within the family Budviciaceae are thus proposed, with the name Jinshanibacter gen. nov., zhutongyuii sp. nov. (type strain CF-458T=CGMCC 1.16483T=GDMCC 1.1586T=JCM 33489T) and Jinshanibacter xujianqingii sp. nov. (type strain CF-1111T=CGMCC 1.16786T=GDMCC 1.1587T=JCM 33490T), respectively.

Six aerobic or facultative anaerobic, motile, Gram-stain-positive, catalase-positive and oxidase-negative strains (zg-Y453T, zg-Y324, zg-Y462T, zg-Y411, zg-Y809T and zg-Y786) were isolated from different faecal samples of Marmota himalayana from the Qinghai–Tibet Plateau. Pale yellow, round, raised and moist colonies appeared 48 h after incubation at 28 °C on brain–heart infusion plates supplemented with 5 % defibrinated sheep blood. According to the 16S rRNA gene sequence alignment, two strain pairs (zg-Y453T/zg-Y324 and zg-Y462T/zg-Y411) shared the highest similarities to Arthrobacter luteolus (99.5 and 99.2 %), and the other one (zg-Y809T/zg-Y786) to Arthrobacter citreus (99.5 %). Results of phylogenetic analysis based on the 16S rRNA gene and genome sequences showed that these six strains represented three separate species within the genus Arthrobacter . The average nucleotide identity and digital DNA–DNA hybridization values between the three novel type strains (zg-Y453T/zg-Y462T/zg-Y809T) and other known species in this genus were all below respective thresholds (70.2–81.5/19.6–24.2 %, 70.6–81.8/19.8–25.0 %, and 70.4–88.2/19.9–35.3 %). Although phylogenetically related, there were obvious chemotaxonomic and phenotypic differences: strain pair zg-Y462T/zg-Y411 had anteiso-C15 : 0 as the only major fatty acid; the three novel species had different dominant quinones, MK-8(H2) in strains zg-Y462T/zg-Y809T (74.8/81.1 %) and MK-8(H2)/MK-9(H2) (43.1/53.0 %) in zg-Y453T; similarly, the ability to reduce nitrate in strains zg-Y453T and zg-Y462T could differentiate them from zg-Y809T. All strains had diphosphatidylglycerol, phosphatidylglycerol and phosphatidylinositol, but differed slightly in the types of unidentified glycolipids, phospholipids and lipids. Based on the results of these polyphasic taxonomic analyses, three novel species within the genus Arthrobacter are proposed, namely Arthrobacter caoxuetaonis sp. nov. (type strain, zg-Y453T=GDMCC 1.2809T=JCM 35173T), Arthrobacter zhangbolii sp. nov. (type strain, zg-Y462T=GDMCC 1.2880T=JCM 35170T) and Arthrobacter gengyunqii sp. nov. (type strain, zg-Y809T=GDMCC 1.2808T=JCM 35168T).