Search and discovery of actinobacteria capable of transforming deoxycholic and cholic acids

Lotus seed resistant starch affects the conversion of sodium taurocholate by regulating the intestinal microbiota

We investigated the ability of lotus seed resistant starch (LRS) to affect the conversion of sodium taurocholate (STCA) by regulating the intestinal flora, using glucose (GLU) and high amylose corn starch (HAMS) as controls. The dominant microbiota in LRS group were mainly Lactobacillus and Escherichia_Shigella, with a small proportion of Bifidobacterium. Meanwhile, Lactobacillus, Bifidobacterium and Enterococcus were dominant microbiota in the HAMS group. Lactobacillus, Burkholderia-Caballeronia-Paraburkholderia and Sphingomonas were found in the GLU group. Furthermore, Bifidobacterium, Enterococcus and Escherichia_Shigella were negatively correlated with STCA and sodium taurodeoxycholate (STDCA), while these bacteria were positively correlated with bile salt hydrolase (BSH) and hydroxysteroid dehydrogenase (HSDH) content. Meanwhile Burkholderia-Caballeronia-Paraburkholderia and Sphingomonas were positively correlated with STCA and STDCA, while these bacteria were negatively correlated with BSH and HSDH content. LRS promoted the proliferation of Bifidobacterium and Escherichia_Shigella to secret more BSH and HSDH, accelerating the hydrolysis of STCA and reducing the conversion of STDCA.

Genome-Wide Transcriptome Profiling Provides Insight on Cholesterol and Lithocholate Degradation Mechanisms in Nocardioides simplex VKM Ac-2033D

Steroid microbial degradation plays a significant ecological role for biomass decomposition and removal/detoxification of steroid pollutants. In this study, the initial steps of cholesterol degradation and lithocholate bioconversion by a strain with enhanced 3-ketosteroid dehydrogenase (3-KSD) activity, Nocardioides simplex VKM Ac-2033D, were studied. Biochemical, transcriptomic, and bioinformatic approaches were used. Among the intermediates of sterol sidechain oxidation cholest-5-en-26-oic acid and 3-oxo-cholesta-1,4-dien-26-oic acid were identified as those that have not been earlier reported for N. simplex and related species. The transcriptomic approach revealed candidate genes of cholesterol and lithocholic acid (LCA) catabolism by the strain. A separate set of genes combined in cluster and additional 3-ketosteroid Δ¹-dehydrogenase and 3-ketosteroid 9α-hydroxylases that might be involved in LCA catabolism were predicted. Bioinformatic calculations based on transcriptomic data showed the existence of a previously unknown transcription factor, which regulates cholate catabolism gene orthologs. The results contribute to the knowledge on diversity of steroid catabolism regulation in actinobacteria and might be used at the engineering of microbial catalysts for ecological and industrial biotechnology.

Bacterial steroid hydroxylases: enzyme classes, their functions and comparison of their catalytic mechanisms

The steroid superfamily includes a wide range of compounds that are essential for living organisms of the animal and plant kingdoms. Structural modifications of steroids highly affect their biological activity. In this review, we focus on hydroxylation of steroids by bacterial hydroxylases, which take part in steroid catabolic pathways and play an important role in steroid degradation. We compare three distinct classes of metalloenzymes responsible for aerobic or anaerobic hydroxylation of steroids, namely: cytochrome P450, Rieske-type monooxygenase 3-ketosteroid 9α-hydroxylase, and molybdenum-containing steroid C25 dehydrogenases. We analyze the available literature data on reactivity, regioselectivity, and potential application of these enzymes in organic synthesis of hydroxysteroids. Moreover, we describe mechanistic hypotheses proposed for all three classes of enzymes along with experimental and theoretical evidences, which have provided grounds for their formulation. In case of the 3-ketosteroid 9α-hydroxylase, such a mechanistic hypothesis is formulated for the first time in the literature based on studies conducted for other Rieske monooxygenases. Finally, we provide comparative analysis of similarities and differences in the reaction mechanisms utilized by bacterial steroid hydroxylases.