Molecular and biochemical properties of the S-layer protein from the wine bacterium Lactobacillus hilgardii B706.

Different strains of the genus Lactobacillus can be regularly isolated from must and wine samples. By various physiological activities, they can improve or reduce the wine quality. Lactobacillus hilgardii that is known to survive under harsh wine conditions is classified as a spoilage bacterium, e.g. due to the production of histamine. Many lactobacilli form an S-layer as the outermost cell wall component which has been found to facilitate the colonization of special ecological niches. A detailed understanding of the properties related to their S-layer proteins is necessary to improve the knowledge of the interactions between different bacterial cells and with the surrounding environments. The S-layer protein from the wine-related L. hilgardii strain B706 has been isolated and its gene sequence determined. The deduced amino acid sequence corresponds to a 41 kDa protein with an isoelectric point of 9.6 without additional posttranslational modifications after splitting off the leader peptide. The complete protein is organized in a 32 amino acids signal sequence for membrane translocation, a positively charged N-terminal domain that binds to the cell wall and a negatively charged C-terminal domain. When the S-layer was removed, the corresponding L. hilgardii B706 cells became more sensitive to bacteriolytic enzymes and some wine-related stress conditions. From a practical point of view, the S-layer may be considered as a target for the inhibition of food-spoiling lactobacilli.