School of Microbiology, University College Cork, Cork, Ireland.
APC Microbiome Institute, University College Cork, Cork, Ireland.
Sci Rep. 2017 Oct 16;7(1):13270. doi: 10.1038/s41598-017-13774-6.
The contribution of the gut microbiota to the metabolism of cholesterol is not well understood. In this study, we identify 21 fosmid clones from a human gut microbiome metagenomic library that, when expressed in Escherichia coli, produce halos on LB agar supplemented with 0.01% (w/v) cholesterol (LBC agar). Analysis of 14 of these clones revealed that they all share a fragment of DNA with homology to the genome of Bacteroides vulgatus. The gene responsible for halo production on LBC agar, named choA, was identified as an N-acyltransferase known to produce an acylated glycine molecule called commendamide. In this study we show that commendamide is capable of producing a halo on LBC agar suggesting that this molecule is solubilizing the cholesterol micelles in LBC agar. We also show that commendamide is responsible for the previously described hemolytic activity associated with the choA orthologue in Bacteroides fragilis. A functional analysis of ChoA identified 2 amino acids that are important for commendamide biosynthesis and we present phylogenetic and functional data showing that orthologues of choA are found only in the order Bacteroidales. Therefore, the production of commendamide may be an adaptation to the environments colonized by the Bacteroidales, including the mammalian gut.
肠道微生物群对胆固醇代谢的贡献还不太清楚。在这项研究中，我们从人类肠道微生物组宏基因组文库中鉴定出 21 个 fosmid 克隆，当在大肠杆菌中表达时，它们会在补充有 0.01%（w/v）胆固醇的 LB 琼脂上产生晕圈（LBC 琼脂）。对其中 14 个克隆的分析表明，它们都与脆弱拟杆菌基因组的一段 DNA 具有同源性。在 LBC 琼脂上产生晕圈的基因名为 choA，被鉴定为一种 N-酰基转移酶，已知能产生一种称为commendamide 的酰化甘氨酸分子。在本研究中，我们表明 commendamide 能够在 LBC 琼脂上产生晕圈，这表明该分子能够溶解 LBC 琼脂中的胆固醇胶束。我们还表明，commendamide 负责先前描述的与脆弱拟杆菌中 choA 同源物相关的溶血活性。对 ChoA 的功能分析确定了 2 个对 commendamide 生物合成重要的氨基酸，我们提出了系统发育和功能数据，表明 choA 的同源物仅存在于拟杆菌目中。因此，commendamide 的产生可能是对拟杆菌目定植的环境的一种适应，包括哺乳动物肠道。
