Abstract
Plasmids in lactic acid bacteria occasionally confer adaptive advantages improving the growth and behaviour of their host cells. They are often associated to starter cultures used in the food industry and could be a signature of their superiority. Oenococcus oeni is the main lactic acid bacteria species encountered in wine. It performs the malolactic fermentation that occurs in most wines after alcoholic fermentation and contributes to their quality and stability. Industrial O. oeni starters may be used to better control malolactic fermentation. Starters are selected empirically by virtue of their fermentation kinetics and capacity to survive in wine. This study was initiated with the aim to determine whether O. oeni contains plasmids of technological interest. Screening of 11 starters and 33 laboratory strains revealed two closely related plasmids, named pOENI-1 (18.3-kb) and pOENI-1v2 (21.9-kb). Sequence analyses indicate that they use the theta mode of replication, carry genes of maintenance and replication and two genes possibly involved in wine adaptation encoding a predicted sulphite exporter (tauE) and a NADH:flavin oxidoreductase of the old yellow enzyme family (oye). Interestingly, pOENI-1 and pOENI-1v2 were detected only in four strains, but this included three industrial starters. PCR screenings also revealed that tauE is present in six of the 11 starters, being probably inserted in the chromosome of some strains. Microvinification assays performed using strains with and without plasmids did not disclose significant differences of survival in wine or fermentation kinetics. However, analyses of 95 wines at different phases of winemaking showed that strains carrying the plasmids or the genes tauE and oye were predominant during spontaneous malolactic fermentation. Taken together, the results revealed a family of related plasmids associated with industrial starters and indigenous strains performing spontaneous malolactic fermentation that possibly contribute to the technological performance of strains in wine.
Highlights
Lactic acid bacteria (LAB) contribute to winemaking during the malolactic fermentation (MLF)
Sequence analysis of pOENI-1 During a survey of O. oeni strains, we have detected a large plasmid in the industrial strain O. oeni C9
The protein encoded by Open reading frames (ORFs) 15 shares more than 70% sequence identity with replication initiator protein A (RepA) encountered in theta type plasmids plca36 of Lactobacillus casei Zhang [42], pLgLA39 of Lactobacillus gasseri LA39 [43] and pSF118-44 of Lactobacillus salivarius UCC118 [44]
Summary
Lactic acid bacteria (LAB) contribute to winemaking during the malolactic fermentation (MLF). O. oeni strains differ considerably in terms of capacity to survive in wine and to conduct MLF. They are more or less tolerant to wine acidity (pH 2.9–4.0), alcohol (11– 17%), phenols and sulfites [6,7]. A few dozens of malolactic starters are available to date They are natural strains selected on the basis of their tolerance to wine stressors, kinetics of MLF, aromas production and safety regarding undesirable metabolisms such as the production of biogenic amines, bitterness or ropiness [10]
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