THE LACTIC-ACID STRESS-RESPONSE OF LACTOCOCCUS-LACTIS SUBSP LACTIS

The lactic acid tolerance response (LATR) of the lactic acid bacterium Lactococcus lactis subsp. lactis has been studied. A dramatic increas e in survival to a severe acid stress (pH 3.9) was obtained by preexpo sing the cells for 30 min to a mildly acid shock at pH 5.5. Whole-cell protein extract analysis revealed that during the acid tolerance resp onse 33 polypeptides are induced over the level of naive cells. Among these are the major heat shock proteins DnaK and GroEL. In conjunction with a previous report (Hartke et al. 1994), the results establish th at L. lactis can adapt to lactic acid exposure in two different ways: a logarithmic phase LATR, which may be activated by protons, and a sta tionary-phase LATR, which needs no activation by protons. Both systems are independent of de novo protein synthesis.