Small heat shock proteins characterization in a probiotic model

Small heat shock proteins (sHSP) are ubiquitous, low molecular weight proteins with chaperon-like activity. sHSP protect cell under stress conditions, critically contributing to survival to heat shock. Lactobacillus plantarum (Lp), a member of the lactic acid bacteria (LAB), is a probiotic species with biomedical and biotechnological applications. Unlike most lactobacilli, which have single shsp genes, three sHSP-encoding genes were identified in Lp WCFS1. Such redundancy might endow Lp with the capacity to cope with a broad range of stresses, thus accounting for its extraordinary environmental adaptability. To unravel the role of Lp sHSP, knock out (KO) mutants for hsp1 and hsp3 were generated and phenotypically characterized. Growth and survival rates under diverse stress conditions, which are typical for probiotics, revealed a different contribute of the two sHSP to thermotolerance induction and cryprotection. However, neither hsp seemed essential to tackle such challenges. Accordingly, cellular protein aggregation in both mutants was not significantly different from the wild type. Comparative transcriptional patterns revealed that in the mutant genetic backgrounds there is an up-regulated basal expression of the un-mutated mate hsp and other stress-related genes genes, which may compensate for the loss of sHSP function, hence underlying the lack of a marked susceptibility to stress. hsp KO affected biofilm adhesive capacity, changed cell surface physicochemical properties, and drastically modified membrane fluidity upon stress. These findings indicate that hsp1 and hsp3 have pleiotropic effects, fulfill overlapping activities in stress tolerance and housekeeping functions, and regulate membrane fluidity by a plausible direct association.