Functional and phenotypic characterization of a protein from Lactobacillus acidophilus involved in cell morphology, stress tolerance and adherence to intestinal cells

Structural components of the cell surface have an impact on some of the beneficial attributes of probiotic bacteria. In silico analysis of the L. acidophilus NCFM genome sequence revealed the presence of a putative cell surface protein that was predicted to be a myosin cross-reactive antigen (MCRA). As MCRAs are conserved among many probiotic bacteria, we used the upp-based counterselective gene replacement system, designed recently for use in L. acidophilus, to determine the functional role of this gene (LBA649) in L. acidophilus NCFM. Phenotypic assays were undertaken with the parent strain (NCK1909) and deletion mutant (NCK2015) to assign a function for this gene. The growth of NCK2015 (Delta LBA649) was reduced in the presence of lactate, acetate, porcine bile and salt. Adhesion of NCK2015 to Caco-2 cells was substantially reduced for both stationary-phase (similar to 45% reduction) and exponential-phase cells (similar to 50% reduction). Analysis of NCK2015 by scanning electron microscopy revealed a longer cell morphology after growth in MRS broth compared to NCK1909. These results indicate a role for LBA649 in stress tolerance, cell wall division and adherence to Caco-2 cells.