Transcriptional Responses of Enterococcus faecalis V583 to Bovine Bile and Sodium Dodecyl Sulfate

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Abstract
Resistance to bile is a prerequisite property of the gastrointestinal bacterial flora. Bile acids are powerful detergents, and resistance to sodium dodecyl sulfate (SDS) has therefore often been considered relevant to studies of bile resistance. We have studied the effects of bovine bile (BB) and SDS on Enterococcus faecalis V583 by traditional growth studies and microarrays. Transcriptional responses were studied by time course experiments. In the presence of BB (V583-BB) or SDS (V583-SDS), 308 and 209 genes were identified as differentially expressed at one or more time points, respectively. In V583 treated with both BB and SDS (V583-BB-SDS), 254 genes showed differential expression. Detergents exert their toxic effects primarily on the microbial membrane. The enrichment of differentially transcribed genes that encode proteins with membrane-associated functions and/or locations indicates a major impact of all three treatments on the integrity and functionality of the cell membrane. Two gene clusters involved in fatty acid biosynthesis were repressed in V583-BB and V583-BB-SDS and partly induced in V583-SDS. Furthermore, two EmrB/QacA family drug resistance transporters and a vacuolar-type ATPase were induced in V583-BB and V583-BB-SDS. None of the putative bile salt hydrolase homologs in V583 showed differential expression during the bile treatments. The transcriptional profile of V583-BB-SDS was qualitatively more similar to the response in V583-BB than to that in V583-SDS, suggesting that the presence of bile suppresses the effects of SDS in V583-BB-SDS. The overall results presented here indicate that different mechanisms are involved in detergent resistance in E. faecalis.