K-110. Characterization of Transporter Proteins Involved in Bile Tolerance in Lactobacillus acidophilus

E. Pfeiler, T. Klaenhammer;
North Carolina State Univ., Raleigh, NC.

Lactobacillus acidophilus NCFM is used industrially as a probiotic culture in yogurt formulations and dietary adjuncts. Tolerance to bile is one important property for microbial survival and competition within the small intestines. Microarray analysis of the transcriptional response of NCFM to bile revealed three transporter genes that were significantly induced upon exposure to 0.5% oxgall. Transporter proteins have been shown previously to play a role in bile tolerance in other bacterial species. LBA1429 (3-fold induction) showed homology to transporters of the major facilitator superfamily and resides within an operon that is induced by oxgall. LBA1446, also annotated as a transporter of the major facilitator superfamily, was shown to be induced 7-fold by oxgall. Also induced (5-fold) was LBA1679 which encodes the permease component of an ABC transporter. LBA0552, a transporter of the major facilitator superfamily, was not induced in the presence of bile. More extensive transcriptional analysis using RT-QPCR indicated that this gene is transcribed at the same level (approximately 3 mRNA copies/cell) in the presence and absence of bile. Derivatives of L. acidophilus NCFM with deletion in each of these four genes were constructed. Each exhibited an increased sensitivity to bile. Growth of the mutant strains was evaluated in the presence of a variety of bile salts, antibiotics, and other compounds, with each derivative exhibiting unique patterns of sensitivity. The results of this study suggest that all three transporters played a role in bile tolerance in L. acidophilus NCFM, and particular transporters play a role in resistance to specific bile salts, erythromycin, and the detergent Triton X-100.