The Asiatic black bear (Ursus thibetanus) is a protected species from eastern Asia. In China, the Asiatic black bear occurs in 17 provinces from northeast to southwest regions. To date, information on microbial diversity in the gut of the Asiatic black bears from different populations remains limited. To determine the species composition and community structure of the gut microbiota in the Asiatic black bear, we characterized 36 fecal samples from Sichuan, Yunnan, and Heilongjiang provinces, China, by pyrosequencing the 16S V3-V4 hypervariable regions using the Illumina Miseq platform. Results showed that Firmicutes and Proteobacteria were the predominant phyla in the samples, which were largely comprised Escherichia-Shigella, Peptostreptococcaceae_incertae_sedis, Turicibacter, Streptococcus, and Clostridium. By analyzing the community structure from these 36 samples, we found that there were significant differences in the species diversity and richness between Sichuan, Yunnan, and Heilongjiang populations. In conclusion, our results reveal the species composition and structure of the gut microbiota in captive black bears in China, and suggest that biogeography could affect the black bear' gut microbiota.

As one of the pro-inflammatory factors, LPS aggravates inflammation through priming neutrophils to synthesize/release cytotoxic contents and prolonging functional lifespan of neutrophils by delaying the spontaneous apoptosis. Thus, our data suggest to us that quercetin might decrease the susceptibility of neutrophils to pro-inflammatory factors (e. g. LPS), which could partially explain the anti-inflammatory mechanisms of quercetin.

Tauroursodeoxycholic acid (TUDCA) has been used to treat many diseases effectively. 7α-hydroxysteroid dehydrogenase (7α-HSDH) and 7β-hydroxysteroid dehydrogenase (7β-HSDH) are two key enzymes that drive the efficient biosynthesis of TUDCA from taurochenodeoxycholic acid (TCDCA) in vitro. In this study, a metagenomic approach was used to isolate 7α- and 7β-HSDHs from fecal samples of black bears. Five new 7α-HSDHs and one new 7β-HSDH enzyme were discovered and identified from the gut microbiota of black bears, and four of them presented good enzymatic properties. Our data also suggest cooperation in the biotransformation of TUDCA by the gut microbiota in black bears. In conclusion, this work expands the natural enzyme bank of HSDHs, provides promising candidate enzymes for application in the biosynthesis TUDCA and the epimerization reaction of bile acids at the C-7 position, and provides a data set for the discovery of novel enzymes in the gut micriobiome of black bears.

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