The role of hypermutability in the evolution of the genus Oenococcus

Robert Mondavi Institute for Wine and Food Sciences, Department of Viticulture and Enology, University of California; National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD

^* To whom correspondence should be addressed. Email: damills{at}ucdavis.edu.

	Abstract

Oenococcus oeni is an alcohol-tolerant, acidophilic lactic acid bacteria primarily responsible for the malolactic fermentation in wine. A recent comparative genomic analysis of O. oeni PSU-1 with other sequenced lactic acid bacteria indicate that PSU-1 lacks the mismatch repair genes mutS and mutL. Consistent with the lack of mismatch repair, mutation rates for O. oeni PSU-1 and a second oenococcal species, O. kitaharae, were higher than that observed from neighboring taxa, Pediococcus pentosaceus and Leuconostoc mesenteroides. Sequence analysis of the rpoB mutations in rifampicin-resistant strains from both oenococcal species revealed a high percentage of transition mutations, a result indicative of the lack of mismatch repair. An analysis of common alleles in the two sequenced O. oeni strains, PSU-1 and BAA-1163 also revealed a significantly higher level of transitions substitutions in comparison to that observed in other Lactobacillales species. These results suggest that the genus Oenococcus is hypermutable due to the loss of mutS and mutL that occurred with the divergence away from the neighboring Leuconostoc branch. The hypermutable status in the genus Oenococcus explains the observed high level of allelic polymorphism among known O. oeni isolates and likely contributed to the unique adaptation of this genus to acidic and alcoholic environments.