High-level resistance to oxidative stress in Lactococcus lactis conferred by Bacillus subtilis catalase KatE.

Lactococcus lactis, a lactic acid bacterium widely used for food fermentations, is often exposed to damaging stress conditions. In particular, oxidative stress leads to DNA, protein and membrane damages that can be lethal. As L. lactis has no catalase, the impact of production of the Bacillus subtilis haem catalase KatE on its oxidative stress resistance was tested. This cytoplasmic catalase was engineered for extracellular expression in L. lactis with an optimization strategy based on fusion to the nisin-inducible promoter and a lactococcal signal peptide (SP(Usp45)). The production of KatE by L. lactis conferred an 800-fold increase in survival after 1 h exposure to 4 mM hydrogen peroxide, and a 160-fold greater survival in long-term (3 days) survival of aerated cultures in a cydA mutant, which is unable to respire. The presence of KatE protected DNA from oxidative damage and limited its degradation after long-term aeration in a cydA/recA mutant, defective in DNA repair. L. lactis is thus able to produce active catalase that can provide efficient antioxidant activity.