Changes in glycolytic activity of Lactococcus lactis induced by low temperature

The effects of low-temperature stress on the glycolytic activity of the lac tic acid bacterium Lactococcus lactis were studied. The maximal glycolytic activity measured at 30 degrees C increased approximately 2.5-fold followin g a shift from 30 to 10 degrees C for 4 h in a process that required protei n synthesis, Analysis of cold adaptation of strains with genes involved in sugar metabolism disrupted showed that both the phosphoenolpyruvate depende nt sugar phosphotransferase system (PTS) subunit HPr and catabolite control protein A (CcpA) are involved in the increased acidification at low temper atures. In contrast, a strain with the PTS subunit enzyme I disrupted showe d increased acidification similar to that in the wild-type strain. This ind icates that the PTS is not involved in this response whereas the regulatory function of 46-seryl phosphorylated HPr [HPr(Ser-P)] probably is involved. Protein analysis showed that the production of both HPr and CcpA was induc ed severalfold (up to two- to threefold) upon exposure to low temperatures, The las operon, which is subject to catabolite activation by the CcpA-HPr( Ser-P) complex, was not induced upon cold shock, and no increased lactate d ehydrogenase (LDH) activity was observed. Similarly, the rate-limiting enzy me of the glycolytic pathway under starvation conditions, glyceraldehyde-3- phosphate dehydrogenase (GAPDH), was not induced upon cold shock. This indi cates that a factor other than LDH or GAPDH is rate determining for the inc reased glycolytic activity upon exposure to low temperatures. Based on thei r cold induction and involvement in cold adaptation of glycolysis, it is pr oposed that the CcpA-HPr(Ser-P) control circuit regulates this factor(s) an d hence couples catabolite repression and cold shock response in a function al and mechanistic way.