Extracellular substances of lactic acid bacteria interests in biotechnological practices applied to enology

Abstract

Extracellular substances (ECS) represent all molecules outside the cytoplasmic membrane, which are not directly anchored to the cell wall of microorganisms living through a planktonic or biofilm phenotype. They are the high-biomolecular-weight secretions from microorganisms (i.e. extracellular polymeric substances – EPS – proteins, polysaccharides, humic acid, nucleic acid), and the products of cellular lysis and hydrolysis of macromolecules. In addition, some high- and low-molecular-weight organic and inorganic matters from environment can also be adsorbed to the EPS. All can be firmly bound to the cell surface, associated with the EPS matrix of biofilm, or released as being freely diffusing throughout the medium. 

In food industry, LAB are commonly studied and used because they can metabolize a wide variety of chemical entities (e.g. acids, carbohydrates…) determining the final product quality and stability. In wine, different LAB species have been identified. Among them, Oenococcus oeni and Lactobacillus plantarum are the two most encountered species and can subsist in wine environments, particularly in barrels in the form of biofilm phenotype. They possibly modify transfers of chemical compounds of interest at the wood/wine interface or actively influence them according to the oenological practices adopted by the winemaker. To control and improve the use of this microbiological flora, it is essential to understand growth dynamics throughout time, particularly by persisting as a biofilm from one vintage to another. 

Up to now, it is still not clear about the ECS composition in wine systems and how they act. Combining different characterization measurements (e.g. mass yields, ATR-FTIR, SEC, LC-MS/MS…) will allow us to determine the role of these ECS during bacterial growth in function of physiological states (planktonic, biofilm) aiming to a better biotechnological control of these bacteria under novel enological practices. 

Physicochemical analyses of the ECS produced by the model Lactobacillus plantarum WCFS1 strain in planktonic and biofilm conditions enable to determine the optimum growing phase for proteinaceous material production by varying growing media (i.e. 3 physicochemical semi-defined media and white grape must). ECS chemical composition unveils the presence of glycosidic enzymes from the same families for the 3 different semi-defined media.