CONICET | Buscador de Institutos y Recursos Humanos

The probiotic Gram-positive bacterium Lactobacillus casei BL23 is naturally confronted with salt stress habitats. It has been previously reported that growth in high salt medium containing 0.8M NaCl leads to modifications in the cell envelope of this bacterium. In this study, we report that L. casei BL23 has an increased ability to form biofilms and to bind cations in high salt conditions. This behavior correlated with modifications of surface properties involving teichoic acids, which are important cell wall components. Also in this high salt condition we showed that L. casei BL23 produces lower level of the cell wall polymer lipoteichoic acid (LTA) and that this anionic polymer has a shorter average chain length and a lower level of D-alanyl-substitution. Moreover analysis of the transcript levels of the dltABCD operon, encoding the enzymes required for the incorporation of D-alanine into anionic polymers, showed a 16-fold reduction in mRNA levels, which is consistent with a decrease in D-alanine substitutions on LTA. Furthermore, a 13-fold reduction in the transcript levels was observed for the gene LCABL_09330 coding for a putative LTA synthase. To provide further experimental evidence that LCABL_09330 is a true LTA synthase (LtaS) in L. casei BL23, the enzymatic domain was cloned and expressed in E. coli. The purified protein was able to hydrolyze the membrane lipid phosphatidylglycerol as expected for an LTA synthase enzyme, and hence LCABL_09330 was renamed LtaS. The purified enzyme showed Mn2+-ion dependent activity, and its activity was modulated by differences in NaCl concentration. The decrease in both ltaS transcript levels and enzyme activity observed in high salt condition might influence the length of the LTA backbone chain. A putative function of the modified LTA structure is discussed that is compatible with the growth under salt stress conditions and with the overall envelope modifications taking place during this stress condition.