Phylogenetic analysis of Lactococcus lactis subspecies based on decoding the sequence of the pepT tripeptidase gene, the pepV dipeptidase gene and 16S rRNA

Tripeptidase (PepT) and dipeptidase (PepV), the enzymes located in the final stage of the intracellular proteolytic system, were demonstrated to be distributed widely in lactic acid bacteria, especially in lactococci. Both the tripeptidase genes (pepT) and dipeptidase genes (pepV) of 15 lactococcal strains consisting of the type and domestic strains were cloned and sequenced using normal and TAIL PCR methods. Amino acid sequences of these enzymes were highly conserved among strains. Evolutionary distance trees based on the sequence of 1239 nucleotides of pepT and 1416 nucleotide of pepV showed a similar cluster as that obtained from the 1499 fragment of the 16S rRNA. Based on this profile, the species Lactococcus lactis is reasonably divided into three subspecies groups, subsp. lactis, cremoris, and hordniae, as in the current classification. Figure of trees from pepT and pepV were essentially identical to each other and slightly more intricate than that from 16S rRNA. The K nuc values obtained from pepT and pepV genes were approximately ten times as high as that from 16S rRNA. Considering these results, phylogenetic analysis based on pepT and pepV genes may aid in a more precise index of classification of L. lactis subspecies. PepT and PepV seem to have evolved in similar directions in lactococci.