Variability in gene content and expression of the thioredoxin system in Oenococcus oeni

•O. oeni PSU-1 genome contains three trxA genes, a trxB gene, and a ferredoxin reductase annotated gene.•trxA1 is present in few O. oeni strains, and it has an HGT origin from Lb. plantarum.•The expression of the thioredoxin system genes in O. oeni is mostly strain-dependent.•trxA3 is overexpressed in all strains and plays a crucial role in the ethanol and acidity stress response.

The thioredoxin system protects against oxidative stress through the reversible oxidation of the thioredoxin active center dithiol to a disulphide. The genome of Oenococcus oeni PSU-1 contains three thioredoxin genes (trxA1, trxA2, trxA3), one thioredoxin reductase (trxB) and one ferredoxin reductase (fdr) which, until recently, was annotated as a second thioredoxin reductase. For the first time, the entire thioredoxin system in several O. oeni strains isolated from wine has been analysed. Comparisons at the DNA and protein levels have been undertaken between sequences from O. oeni and other genera and species, and the genera Leuconostoc and Lactobacillus were found to present the highest similarities. The gene most frequently absent from a collection of 34 strains and the sequences annotated in the NCBI database was trxA1. Moreover, phylogenetic analysis suggested that this gene was horizontally transferred from Lactobacillus to O. oeni. Strain-dependent expression profiles were determined in rich and in wine-like media. General over-expression was detected after inoculation into wine-like medium, with trxA3 being the most highly expressed gene. The increased transcriptional levels of the thioredoxin genes are indicative of the crucial role of this system in the O. oeni response to wine harsh conditions.