Evidence of mixed wild populations of Oenococcus oeni strains during wine spontaneous malolactic fermentations

Two hundred and four bacterial isolates from Rioja red wines undergoing spontaneous malolactic fermentation (MLF) were studied. Bacterial species was determined both by microbiological identification methods and by specific PCR analysis. Oenococcus oeni was shown to be the predominant species (98.5% of total isolates). Pulsed field gel electrophoresis (PFGE) of chromosomal DNA digested with SfiI was used to differentiate individual strains of O. oeni. A wide variety of restriction digest patterns were detected, which indicated a rich biodiversity of indigenous strains. Most fermentations (37 out of 41) showed from 2 to 6 clones growing in the same tank. Five O. oeni strains were the most frequently found, appearing in more than three of the 13 studied wineries, and most times in combination with other less frequently found strains. PFGE was shown to be a suitable method for strain differentiation, for monitoring individual strains and determining which strains actually survive and carry out MLF. A high genotypic heterogeneity of wild O. oeni strains was demonstrated and 90% of the studied wines showed mixed populations of O. oeni strains during MLF.