Autolysis of Lactococcus lactis

During cheese making, autolysis of Lactococcus lactis starter bacteria affects cheese flavour development through release of intracellular enzymes. The gene for the major autolysin in L. lactis, N-acetyl muramidase (AcmA), has been cloned and sequenced. The activity of AcmA alone, however, does not explain the huge variation in the extent of autolysis found in commercial L. lactis starter strains. Many such strains have multiple cell wall hydrolases that can be seen as different sized clearance bands in zymograms. In addition, the recently completed L. lactis subsp. lactis IL1403 genome sequence shows the presence of several open reading frames that putatively encode cell wall hydrolases having up to 42% predicted amino acid identity to AcmA. These enzymes could have roles in the autolysis of L. lactis. In this paper, we review the literature on autolysis of L. lactis and provide experimental evidence, based on Western blot and zymogram analysis, that commercial L. lactis starter strains express varying levels of AcmA and contain other cell wall hydrolases.