Polysaccharides of the lactic acid bacterium Oenococcus oeni : from structure and biosynthetic pathway determination to technological implementation – OENOPOLYS

Twenty genomes of O. oeni strains representative of the species and its various exopolysaccharide phenotypes were sequenced and the genes dedicated to the metabolism of exopolysaccharides (homo and heteropolysaccharides) were identified. Cloning of glycosyltransferases representative is underway in parallel with the characterization of polymers and enzymes produced by wild strains.

All the strains studied are equipped with several genes encoding different EPS biosynthetic pathways, although they produce highly different levels of soluble EPS concentration in model media. The analysis of 20 genomes indicates the presence of two dextransucrase genes, a levansucrase gene, an isolated gene encoding an autonomous processive glycosyltransferase and two operons potentially associated with heteropolysaccharide (HEPS) synthesis.

The characterization of enzymes and polymers is underway.

One article in Int J Food microbiol. Two posters in National conferences.

Apart from plant polysaccharides, microbial polysaccharides are receiving growing interest. Indeed, some display novel chemical structures associated with unique behavior in solution, which can be very interesting for the food industry. Lactic acid bacteria have the GRAS status and are used in traditional as well as in industrial food fermentations. Among them, Oenococcus oeni is of interest because it has a small, rapidly evolving genome and a specific ecological niche restricted to wine. Bacteria belonging to this species perform malolactic fermentation (MLF) in most wines in temperate regions, either spontaneously (indigenous grapes flora) or after addition of strains selected and produced industrially (commercial malolactic starters). The ability of malolactic starters to produce exopolysaccharides (EPS) is not so far a criterion used during selection. However, this property could be crucial, when considering the potential impact of these polysaccharides on the colloidal stability and organoleptic properties of wine. The EPS produced by O. oeni could also protect the bacteria during their industrial production, their storage or during their inoculation into the wine (providing resistance to acid shock, ethanol or phages). The tremendous diversity within the O. oeni species is currently assessed in the DivOeni (2008-2011) ANR project. As part of these studies, different strains of O. oeni with outstanding EPS production have been identified. The structure of these polymers, the genes dedicated to their production and export, the impact of EPS on wine quality and their biological role are still unknown. The current project aims to address these major issues and will bring together three academic partners who are key experts in the field in a collaborative effort, as well as an industrial partner, leader in the selection and production of enological starters. The project is expected to provide the following essential results: i; a comprehensive inventory of genes dedicated to the synthesis of EPS in the species O. oeni with particular attention to strains showing remarkable phenotypes, ii; the identification of the polysaccharides structures, iii; the respective role of each glycosyltransferase involved in the synthesis, iv; the interactions and physiological consequences of the presence of several polysaccharides biosynthetic pathways within a given O. oeni strain- which is frequent in the species- , v; the technological interest of the polysaccharides and of the producing-strains when they are used as additives during winemaking (impact of the colloidal stability and palatability), and vi; ,more sustainable processes for starter production and storage enhancing the resistance of starters by stimulating the EPS formation may be developed. The latter result might have a strong impact on winemaking practices as it might reduce the cost of industrial malolactic starters and enable to generalize their use by winemakers, thus producing wines of better quality, under controlled conditions, and with a reduced electric or energetic consumption.