Identification of variable genomic regions related to stress response in Oenococcus oeni.

The lactic acid bacterium Oenococcus oeni is the most important species involved in malolactic fermentation due to its capability to survive in presence of ethanol and in the acidic environment of wine. In order to identify novel genes involved in adaptation to wine, a new approach using genome-wide analysis based on stress-related genes was performed in strain O. oeni PSU-1, and 106 annotated stress genes were identified. The in silico analysis revealed the high similarity of all those genes through 57 O. oeni genomes; however, seven variable regions of genomic plasticity could be determined for their different presence observed among these strains. Regions 3 and 5 had the typical hallmarks of horizontal transfer, suggesting that the strategy of acquiring genes from other bacteria enhanced the fitness of O. oeni strains. Certain genes related to stress resistance were described in these regions, and similarities of putative acquired regions with other lactic acid bacteria species were found. Some genomic fragments present in all the strains were described and another new genomic island harbouring a threonine dehydrogenase was found. The association of selected sequences with adaptation to wine was assessed by screening 31 O. oeni strains using PCR of single genes, but no sequences were found to be exclusive to highly performing malolactic fermentation strains. This study provides new information about the genomic variability of O. oeni strains contributing to a further understanding of this species and the relationship of its genomic traits with the ability to adapt to stress conditions.