Lactobacillus vini: mechanistic response to stress by medium acidification

This work describes the response of Lactobacillusvini, a bacterium found as a contaminant in winemaking and fuel ethanol fermentation processes, to acid stress caused by inorganic or weak organic acids. First, we observed for the first time that bacterial cells become resistant to lysis by lysozyme when submitted to acidic stress. Then, the predicted intracellular acidification can be reversed by the presence of arginine, histidine and glutamine. However, these molecules were not able to reverse the effect of resistance to lysis, indicating the independence of these mechanisms. In general, a reduction in the expression of the main genes involved in the synthesis and deposition of material in the cell wall was observed, whereas the genes involved in the reabsorption of this structure showed increased expression. These data suggested that L. vini responds to the acidification of the medium through early entry into the stationary phase, firing two signals for cell wall remodelling and maintenance of intracellular pHin a coordinated way, most probably by alkalization and the proton extrusion process. If this picture is conserved among lactobacilli, it may not only have an impact on research associated with fermentation processes, but also on that associated with probiotic improvement.