Characterization of a Novel Bile-Inducible Operon Encoding a Two-Component Regulatory System inLactobacillus acidophilus

Abstract

Lactobacillus acidophilus NCFM is an industrially important strain used extensively as a probiotic culture. Tolerance of the presence of bile is an attribute important to microbial survival in the intestinal tract. A whole-genome microarray was employed to examine the effects of bile on the global transcriptional profile of this strain, with the intention of elucidating genes contributing to bile tolerance. Genes involved in carbohydrate metabolism were generally induced, while genes involved in other aspects of cellular growth were mostly repressed. A 7-kb eight-gene operon encoding a two-component regulatory system (2CRS), a transporter, an oxidoreductase, and four hypothetical proteins was significantly upregulated in the presence of bile. Deletion mutations were constructed in six genes of the operon. Transcriptional analysis of the 2CRS mutants showed that mutation of the histidine protein kinase (HPK) had no effect on the induction of the operon, whereas the mutated response regulator (RR) showed enhanced induction when the cells were exposed to bile. These results indicate that the 2CRS plays a role in bile tolerance and that the operon it resides in is negatively controlled by the RR. Mutations in the transporter, the HPK, the RR, and a hypothetical protein each resulted in loss of tolerance of bile. Mutations in genes encoding another hypothetical protein and a putative oxidoreductase resulted in significant increases in bile tolerance. This functional analysis showed that the operon encoded proteins involved in both bile tolerance and bile sensitivity.

Transcriptional and functional analysis of galactooligosaccharide uptake bylacSinLactobacillus acidophilus

“…It was found that GOS specifically induced a cluster of genes encoding intracellular proteins involved with galactose and lactose metabolism, notably a LacS permease implicated in GOS transport. The GOS-induced gene cluster was previously identified to be up-regulated by both lactose and bile acids (26,46), validating a role in metabolism of lactose-derived GOS and suggesting an adaptive combination of GIT-evolved traits for energy metabolism and bile tolerance.…”

Stress Physiology of Lactic Acid Bacteria

“…For example, an eight-gene operon encoding a TCS, a transporter, an oxidoreductase, and four hypothetical proteins has been implicated in sensing bile salt in Lb. acidophilus (468). Likewise, the genes encoding multidrug transporters driving extrusion of bile salts are upregulated in Lb.…”

Allelic Variation of Bile Salt Hydrolase Genes in Lactobacillus salivarius Does Not Determine Bile Resistance Levels

“…In addition to bsh, other genes (pva and btlB) and the sigma factor B have been shown to contribute to bile resistance in L. monocytogenes EGDe (3). Furthermore, microarray analysis of the bile-induced transcriptome identified genes, including those encoding multidrug resistance (MDR) transporters, chaperone, esterase, and a histidine protein kinase, that were implicated in bile resistance in L. acidophilus NCFM and Lactobacillus reuteri ATCC 55730 (45,62). Genes involved in DNA repair, oxidative response, transcriptional regulation, dGTP hydrolysis, membrane composition, and cell wall synthesis were differentially expressed upon exposure of Enterococcus faecalis or L. plantarum WCFS1 cells to bile (6,7).…”