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. 2022 May 11;13:899102. doi: 10.3389/fmicb.2022.899102

Figure 4.

Figure 4

Association between BAs composition and gut microbial diversity. (A) Heat map summarizing the correlations of fecal bile acid concentrations and differentially abundant taxa relative abundance between groups (*p < 0.05; **p < 0.01). (B) Secondary BAs metabolic pathways modified by the microbiome. (a) BSH deconjugation of T/GCA and T/GCDCA. (b) 7α/β-dehydroxylation of CA and CDCA. (c) 7α/β-dehydrogenation of CA and DCA. (d) 3α/β-dehydrogenation of CA and CDCA. The hydrolysis of taurine or glycine conjugated BAs to free BAs is performed by the bacterial bile salt hydrolase (BSH; K01442; Di Ciaula et al., 2017). In addition, following deconjugation, gut microbiota can perform 7-dehydroxylation, involving a multistep biochemical pathway found only in anaerobic gut bacteria (7-dehydroxylation: K15868, K15869, K15870, K15871, K15872, K15873, K15874, and K07007; Monte et al., 2009), bacterial dehydratases of the anaerobic flora from this region attack and remove the hydroxyl group to form 7-deoxy BAs (Monte et al., 2009), including 7α-dehydroxylation of CA and CDCA yielding DCA and LCA, respectively; BAs 7β-dehydroxylation of UDCA yielding LCA (Di Ciaula et al., 2017). Another well-recognized transformation is carried out by hydroxysteroid dehydrogenases (HSD) of intestinal bacteria (Monte et al., 2009; Ridlon et al., 2016; Lucas et al., 2021). HSDs catalyze reversible oxidation of hydroxyl groups on the C-3 (3α-HSD: K22604, K22605; 3β-HSD: K22606, K22607) and C-7 (7α-HSD: K00076; 7β-HSD: K23231) carbon positions of the bile acid steroid core (Monte et al., 2009; Ridlon et al., 2016; Lucas et al., 2021).