A study into the role of L-aspartic acid on the metabolism of L-malic acid and D-glucose by Oenococcus œni Y. Vasserot, C. Dion, E. Bonnet, A. Maujean and P. Jeandet Laboratoire d’Oenologie, Faculte´ des Sciences, Reims, France 534/9/00: received 4 September 2000, revised 3 November 2000 and accepted 13 November 2000 Y. VASSEROT, C. DION, E. BONNET, A. MAUJEAN AND P. JEANDET. 2001. Aims: The purpose of this work was to study the effect of L-aspartic acid concentration on bacterial growth, D-glucose fermentation and L-malic acid consumption of Oenococcus œni NCFB 1707. Methods and Results: Bacterial cultures were performed in synthetic media. Bacterial growth, D-glucose fermentation and L-malic acid consumption were reduced when L-aspartic acid concentration became excessive. This inhibitory effect of high concentrations of L-aspartic acid on bacterial growth was also observed with several Oenococcus œni strains, except O. œni BL01. The L-aspartic acid inhibitory effect on bacterial growth could be reduced by increasing the concentration of L-glutamic acid. L-glutamic acid transport was found to be competitively inhibited by L-aspartic acid. In addition, an excessive amount of L-aspartic acid modified D-glucose metabolism, with an overproduction of acetic acid and reduced ethanol production. Conclusions: Since L-glutamic acid is an essential amio acid for the bacterial strain used, the L-aspartic acid inhibitory effect on bacterial growth could be linked to its involvement in an antagonistic interaction with L-glutamic acid. Significance and Impact of the Study: Such antagonistic interactions between amino acids in O. œni strains could be another explanation for the difficulties of inducing malolactic fermentation in wines. INTRODUCTION Nowadays, malolactic fermentation (MLF) is a very important stage of sparkling wine production (Beelman and Galander 1979). The conversion of L-malic acid into L-lactic acid and carbonic gas by lactic acid bacteria reduces the acidity in white wines and makes them microbiologically more stable (Kunkee 1967). In addition, some metabolism of these micro-organisms can change favourably the flavour of the wine (Rodriguez et al. 1990). MLF should occur before bottling in order to prevent subsequent bacterial develop- ment which would form undesirable deposits (Valade et al. 1984; Davis et al. 1985). For these reasons, and because improved sanitary conditions in winemaking have resulted in the production of wines in which MLF may not occur spontaneously, or may be very unpredictable, many wine- makers have tried to induce MLF with starter cultures developed from freeze-dried or frozen Oenococcus œni biomass (Lafond-Lafourcade et al. 1983 1 ). Nevertheless, despite the use of these starter cultures, MLF very often remains difficult to induce, more specifically in Champagne wines. Difficulties in inducing MLF are usually attributed to the cumulative inhibitory effect of low pH, high alcohol and SO 2 content of wines (Wibowo et al. 1988; Britz and Tracey 1990). However, these difficulties are also thought to have, as their origin, the nutrient composition 2 of wines. The present hypothesis is that the free amino acid content of wines could be of great significance. Colagrande et al. (1984) reported the presence of only small amounts (less than 10 mg l )1 ) of methionine, leucine or isoleucine in Cham- pagne-based wine. To date, few studies have focused on the amino acid requirements of O. œni. Garvie (1967) deter- mined the essential amino acids for growth but did not study their effect on malolactic conversion. Tracey and Britz (1989) 3 carried out a complete study of MLF but examined the influence of only six amino acids. Fourcassie et al. 4 (1992) studied the effect of 18 amino acids on growth, fermentation of D-glucose and malolactic activity of six strains of Correspondence to: Dr Y. Vasserot, Laboratoire d’Oenologie, URVVC, UPRES EA 2069, Faculte´des Sciences, BP 1039, 51687 Reims Cedex 02, France (e-mail: yann.vasserot@univ-reims.fr) ª 2001 The Society for Applied Microbiology Journal of Applied Microbiology 2001, 90, 380–387