Influence of environmental conditions and AI2 on the adhesion adaptive response of Lactobacillus acidophilus NCFM

This study reports an over 20-fold increase in the adhesive ability of Lactobacillus acidophilus NCFM to Caco-2 cells following a 1 hour incubation of cells that were concentrated ten-fold, immediately prior to adhesion. Microarray analysis of the global transcriptional response with and without exposure to the adhesion adaptive conditions revealed several genes potentially involved with adhesion to the intestinal epithelial cells and a classic stress response. Interestingly, putative genes linked to the synthesis of an interspecies signaling molecule, autoinducer-2 (AI-2), were overexpressed. Examination of the L. acidophilus NCFM genome revealed the complete pathway for AI-2 synthesis. AI-2 activity was detected in L. acidophilus NCFM during stationary growth phase using the Vibrio harveyi BB170 assay system. Using site-specific integration, an isogenic mutation was created in luxS and the resulting derivative of L. acidophilus NCFM did not produce AI-2. A 58 % decrease in adherence to Caco-2 cells was also observed by the LuxS- mutant when the cells were used for adhesion directly from logarithmic phase cultures. However, the LuxS- mutant strain still responded to adhesion adaptive conditions with significantly increased adherence indicating that additional factors contribute to the amplified adhesion response. Keywords: Culture response to specific environmental conditions A single 20 mL culture of L. acidophilus was grown in MRS to OD600 of 0.6, divided into two 10 ml aliquots, and harvested by centrifugation for 8 min at 3,150 x g. One aliquot was resuspended in 10 ml of fresh MRS (Sample "control"), the other resuspended in 1 ml of fresh MRS (Sample "test"). Both cultures were then incubated for 1 hr at 37°C. Following incubation, cells were harvested by centrifugation and frozen immediately in a dry ice-ethanol bath. RNA isolation was conducted according to the protocol described previously (Azcarate-Peril et al., 2005). Two slides, each containing the complete genome of L. acidophilus NCFM spotted in triplicate, were hybridized reciprocally to Cy3- and Cy5-labeled probes per experiment (dye swap) for each of two biological replicates.