Department of Dairy, Fat and Cosmetics, University of Chemistry and Technology, Technická 5, 166 28 Prague, Czech Republic.
Department of Biochemistry and Microbiology, University of Chemistry and Technology, Technická 5, 166 28 Prague, Czech Republic.
Biotechnol Adv. 2018 May-Jun;36(3):682-690. doi: 10.1016/j.biotechadv.2017.12.005. Epub 2017 Dec 14.
An important feature of the intestinal microbiota, particularly in the case of administered probiotic microorganisms, is their resistance to conditions in the gastrointestinal tract, particularly tolerance to and growth in the presence of bile salts. Bacteria can use several defence mechanisms against bile, including special transport mechanisms, the synthesis of various types of surface proteins and fatty acids or the production of exopolysaccharides. The ability to enzymatically hydrolyse bile salts occurs in a variety of bacteria. Choloylglycine hydrolase (EC 3.5.1.24), a bile salt hydrolase, is a constitutive intracellular enzyme responsible for the hydrolysis of an amide bond between glycine or taurine and the steroid nucleus of bile acids. Its presence was demonstrated in specific microorganisms from several bacterial genera (Lactobacillus spp., Bifidobacterium spp., Clostridium spp., Bacteroides spp.). Occurrence and gene arrangement encoding this enzyme are highly variable in probiotic microorganisms. Bile salt hydrolase activity may provide the possibility to use the released amino acids by bacteria as sources of carbon and nitrogen, to facilitate detoxification of bile or to support the incorporation of cholesterol into the cell wall. Deconjugation of bile salts may be directly related to a lowering of serum cholesterol levels, from which conjugated bile salts are synthesized de novo. Furthermore, the ability of microorganisms to assimilate or to bind ingested cholesterol to the cell wall or to eliminate it by co-precipitation with released cholic acid was also documented. Some intestinal microflora produce cholesterol reductase that catalyses the conversion of cholesterol to insoluble coprostanol, which is subsequently excreted in faeces, thereby also reducing the amount of exogenous cholesterol.
肠道微生物群的一个重要特征，特别是在给予益生菌微生物的情况下，是它们对胃肠道条件的抵抗力，特别是对胆盐的耐受性和在存在胆盐的情况下的生长。细菌可以使用几种防御机制来对抗胆汁，包括特殊的运输机制、各种类型的表面蛋白和脂肪酸的合成或胞外多糖的产生。许多细菌都具有酶解胆盐的能力。胆盐水解酶（EC 3.5.1.24）是一种组成型细胞内酶，负责水解甘氨酸或牛磺酸与胆汁酸的甾体核之间的酰胺键。它存在于来自几个细菌属（乳杆菌属、双歧杆菌属、梭菌属、拟杆菌属）的特定微生物中。该酶的存在及其编码基因的排列在益生菌微生物中高度可变。胆盐水解酶活性可以为细菌提供释放的氨基酸作为碳和氮源的可能性，有助于胆汁解毒或支持胆固醇掺入细胞壁。胆盐的去共轭可能与血清胆固醇水平的降低直接相关，而共轭胆盐是从头合成的。此外，微生物同化或结合摄入的胆固醇到细胞壁或通过与释放的胆酸共沉淀来消除胆固醇的能力也有记录。一些肠道微生物群产生胆固醇还原酶，该酶催化胆固醇转化为不溶性粪甾醇，随后随粪便排出体外，从而也减少了外源性胆固醇的量。
