An essential role for arginine catabolism in the acid tolerance of Lactococcus lactis MG1363

During anaerobic growth, the neutrophilic bacterium Lactococcus lactis produces lactic acid which leads to medium acidification until a pH of about 4.5. L. lactis MG1363 can develop an adaptive response to acidity commonly referred to as acid tolerance response (ATR). ATR dramatically improves the acid tolerance of the strain and can be induced by incubation at pH 5. Using two-dimensional protein electrophoresis, we found that ornithine carbamoyl transferase (ArcB) is induced during the development of ATR in chemically-defined medium. To determine its importance in acid tolerance of L. lactis, the corresponding gene was mutagenized. We showed that the arcB mutant is more sensitive to acidity than the wild-type strain. We also demonstrated that L. lactis displays an arginine-dependent ATR in defined medium. Altogether, our results suggest a crucial role for the arginine deiminase pathway in the acid tolerance of L. lactis MG1363.