PROTEOMIC STUDY OF THE USE OF MANNOPROTEINS BY OENOCOCCUS OENI TO IMPROVE MALOLACTIC FERMENTATION

Abstract

Malolactic fermentation (MLF) is a desired process to decrease acidity in wine. This fermentation, carried out mostly by Oenococcus oeni, is sometimes challenging due to the wine stress factors affecting this lactic acid bacterium. Wine is a harsh environment for microbial survival due to the presence of ethanol and the low pH, and with limited nutrients that compromise O. oeni development. This may result in slow or stuck fermentations. After the alcoholic fermentation the nutrients that remain in the medium, mainly released by yeast, can be used in a beneficial way by O. oeni during MLF. Among them, mannoproteins stand out, being the main component of the yeast cell wall. These polysaccharides are released in different amounts during the winemaking process in alcoholic fermentation and aging on the lees. It has been described that the mannoproteins released by yeasts can activate the development MLF due to detoxification but little is known about the possible metabolization of mannoproteins by O. oeni.

The aim of this work was to evaluate the changes in the proteome of O. oeni PSU-1 due to the presence of mannoproteins. The addition of 2 g/L of a purified extract of mannoproteins resulted in the decrease of the duration of MLF in wine synthetic medium. This could be correlated to the decrease in mannoprotein content after MLF.  Proteomic analysis of O. oeni cells allowed the identification a total of 956 proteins. From these, 59 showed significant differences in abundance due to mannoprotein presence. On one side, the functional category of carbohydrate transport and metabolism was the most affected by mannoprotein addition and represented 25% of the proteins showing an increased abundance with respect to the control condition. Remarkably, one protein with increased abundance was a permease of the phosphotransferase system (PTS). Mannose, which can be liberated from mannoproteins as a result of O. oeni mannosidase activity, has been described as a PTS substrate, and could be implicated in O. oeni growth stimulation [1, 2]. On the other side, amino acid transport and metabolism, together with translation, were the functional categories that showed a higher number of proteins with decreased abundance in comparison to the control condition. In conclusion, O. oeni PSU-1 proteome was modified due to mannoprotein addition, indicating the metabolic use of these compounds that resulted in a stimulatory effect on MLF.

1. Diez L, Guadalupe Z, Ayestarán B, Ruiz-Larrea F. (2010) Effect of yeast mannoproteins and grape polysaccharides on the growth of wine lactic acid and acetic acid bacteria. J Agric Food Chem 58 (13):7731-9. doi: 10.1021/jf100199n
2. Jamal Z, Miot-Sertier C, Thibau F, Dutilh L, Lonvaud-Funel A, Ballestra P, Le Marrec C, Dols-Lafargue M. (2013) Distribution and functions of phosphotransferase system genes in the genome of the lactic acid bacterium Oenococcus oeni. Appl Environ Microbiol 79 (11): 3371-9. doi: 10.1128/AEM.00380-13