Comparative genomics and phenotypes of Oenococcus alcoholitolerans and Oenococcus oeni, two sister species adapted to ethanol-rich environments.

From the genus Oenococcus, the most studied species is O. oeni due to its role in malolactic fermentation (MLF) during the winemaking process. In 2014, a new member of the genus -alongside O. kitaharae and O. sicerae- was discovered: O. alcoholitolerans. Whereas O. oeni is found in oenological matrixes, from grapes to wine, O. alcoholitolerans is found in cachaça residues and bioethanol fermentation. Though these ecological niches are different, they share the presence of high ethanol concentrations, which could be related to their evolutionary adaptation. This study provides the first sequenced and circularized genome of O. alcoholitolerans (UFRJ-M7), which was used for a comparative genomic analysis with the species O. oeni. In addition, the physiological traits of both species were compared regarding malolactic fermentation performance and survival in conditions of increasing ethanol and acid. The results showed great genetic differences in genes related to defence mechanisms, transcriptional factors, and some aspects of metabolism, such as sugar catabolism, purine/pyrimidine, coenzyme and vitamin biosynthesis. All these variations can be attributed to the specific adaptations of O. oeni and O. alcoholitolerans to their respective ecological niches. Notably, O. alcoholitolerans has not been detected in analyzed wine samples. This observation aligns with laboratory-based physiological tests, which demonstrated that the combined stress of ethanol and low pH prevented the survival of O. alcoholitolerans, despite its ability to carry out the MLF.