Elkins C A, Moser S A, Savage D C
Department of Microbiology, M409 Walters Life Sciences Bldg, University of Tennessee, Knoxville, TN 37996-0845, USA.
Microbiology (Reading). 2001 Dec;147(Pt 12):3403-12. doi: 10.1099/00221287-147-12-3403.
Lactobacillus johnsonii strain 100-100 expresses two antigenically distinct conjugated bile salt hydrolases (BSH), alpha and beta, that combine to form native homo- and heterotrimers. This paper reports characterization of loci within the genome that encode this capacity. A locus that encodes BSH beta (cbsH beta), a partial (cbsT1) and a complete conjugated bile salt transporter (cbsT2) was identified previously. DNA sequence analysis at this locus was extended and revealed a complete ORF for cbsT1 and no other ORFs in tandem. The three genes, cbsT1, cbsT2 and cbsH beta, probably constitute an operon; a putative promoter was identified upstream of cbsT1. A second locus that expresses BSH activity in strain 100-100 was identified. Sequence analysis of the clone predicted a 978 nt ORF that did not share tandem organization with other ORFs, was similar in sequence to other BSH genes, and matched, in predicted protein sequence, the first 25 amino acids of BSH alpha. A phenotypic screen for BSH activity and a genetic screen for the cbsH beta locus were performed on 50 Lactobacillus isolates from humans or dairy products. Nearly all of the isolates that were positive for cbsH beta were from human sources. Variability in the BSH phenotype and cbsH beta genotype was identified in isolates of the same species. DNA sequence was obtained and analysed from the cbsH beta locus of one human isolate, L. acidophilus strain KS-13. This organism has cbsT1, cbsT2 and cbs beta genes that are 84, 87 and 85% identical in DNA sequence to those of strain 100-100. DNA sequence identity to strain 100-100 ends in regions flanking this locus. The findings of this study suggest that BSH genes have been acquired horizontally and that BSH activity is important at some level for lactobacilli to colonize the lower gastrointestinal tract.
约氏乳杆菌100 - 100菌株表达两种抗原性不同的共轭胆汁盐水解酶（BSH），即α和β，它们结合形成天然的同三聚体和异三聚体。本文报道了基因组中编码这种能力的基因座的特征。先前已鉴定出一个编码BSHβ（cbsHβ）、一个部分共轭胆汁盐转运体（cbsT1）和一个完整共轭胆汁盐转运体（cbsT2）的基因座。对该基因座的DNA序列分析得到扩展，揭示了cbsT1的完整开放阅读框（ORF），且没有串联的其他ORF。这三个基因，cbsT1、cbsT2和cbsHβ，可能构成一个操纵子；在cbsT1上游鉴定出一个推定的启动子。在约氏乳杆菌100 - 100菌株中鉴定出了第二个表达BSH活性的基因座。对该克隆的序列分析预测了一个978 nt的ORF，它不与其他ORF串联排列，在序列上与其他BSH基因相似，并且在预测的蛋白质序列上与BSHα的前25个氨基酸匹配。对来自人类或乳制品的50株乳杆菌分离株进行了BSH活性的表型筛选和cbsHβ基因座的遗传筛选。几乎所有cbsHβ呈阳性的分离株都来自人类来源。在同一物种的分离株中鉴定出了BSH表型和cbsHβ基因型的变异性。从一株人类分离株嗜酸乳杆菌KS - 13的cbsHβ基因座获得并分析了DNA序列。该菌株的cbsT1、cbsT2和cbsβ基因在DNA序列上与100 - 100菌株的相应基因分别有84%、87%和85%的同一性。与100 - 100菌株的DNA序列同一性在该基因座两侧区域终止。本研究结果表明，BSH基因是通过水平转移获得的，并且BSH活性在某种程度上对于乳杆菌定殖于下胃肠道很重要。
