Abstract
The wine lactic acid bacteria Oenococcus ?ni has to cope with harsh environmental conditions including an acidic pH, a high alcoholic content, non-optimal growth temperatures, and growth inhibitory compounds such as fatty acids, phenolic acids and tannins. We here describe characterisation and cloning of the O. ?ni omrA gene encoding a protein belonging to the ATP-binding cassette superfamily of transporters. The OmrA protein displays the highest sequence similarity with the subfamily of ATP-dependent multidrug resistance (MDR) proteins, most notably the bacterial Lactococcus lactis LmrA homologue of the human MDR1 P-glycoprotein. The omrA gene proved to be a stress-responsive gene since its expression was increased at high temperature or under osmotic shock. The OmrA protein function was tested in Escherichia coli, and consistent with the omrA gene expression pattern, OmrA conferred protection to bacteria grown on a high salt medium. OmrA also triggered bacterial resistance to sodium laurate, wine and ethanol toxicity. The homologous LmrA protein featured the same stress-protective pattern than OmrA when expressed in E. coli, and the contribution to resistance of both OmrA and LmrA transporters was decreased by verapamil, a well-known inhibitor of the human MDR1 protein. Genes homologous to omrA were detected in other wine lactic acid bacteria, suggesting that this type of genes might constitute a well-conserved stress-protective molecular device.
Article Outline
1. Introduction
2. Materials and methods
2.1. Materials
2.2. Strains and growth conditions
2.3. Plasmids used
2.4. Construction of a probe specific to the omrA gene of O. ?ni
2.5. Southern blot analysis
2.6. Cloning of the O. ?ni omrA gene by inverse PCR
2.7. RNA isolation and RT-PCR analysis
2.8. Resistance assays
3. Results
3.1. Cloning of the O. ?ni MDR1-homologous omrA gene
3.2. The omrA gene is a stress-responsive gene
3.3. The Omra and Lmra proteins protect bacteria against multiple stress
3.4. Homologous genes in other lactic acid bacteria
4. Discussion
Acknowledgements
References