Genetic Manipulation of the Peptidolytic System in Lactic Acid Bacteria

Due to their presumed involvement in product flavour the peptidases of lactic acid bacteria have been subject to extensive research. A major breakthrough was the isolation and purification of the various enzymes to homogeniety. This allowed a reevaluation of the number of different enzymes in one species by careful investigation of their specficities. Moreover, the purified proteins offered novel ways to the genetic analysis of the peptidolytic system. N-terminal amino acid sequences of, and antibodies against, the purifiied peptidases were used to clone the majority of peptidases described for Lactococcus lactis. Some peptidase genes, especially those from a number of lactobacilli, were obtained by complementation of peptidase-negative cloning hosts. Thus, by deduction, the amino acid sequences of these peptidases is known and all belong to known families of peptidases. The recently developed chromosomal integration svstems for LAB have been used to construct (multiple) peptidase-negative mutants in L. lactis. The growth characteristics of these strains are now under study. As a number of the mutants were made in a food grade way their performance in cheesemaking can be evaluated. The review presented will focus on the latest developments in the genetic analysis of peptidases in LAB and will evaluate our current understanding of peptidolvsis by LAB and its importance in dairy fermentations.