Lactococcus lactis LM0230 contains a single aminotransferase involved in aspartate biosynthesis, which is essential for growth in milk

Amino acid aminotransferases (ATases), which catalyse the last biosynthetic step of many amino acids, may have important physiological functions in La ctococcus lactis during growth in milk. In this study, the aspartate ATase gene (aspC) from L. lactis LM0230 was cloned by complementation into Escher ichia coli DL39. One chromosomal fragment putatively encoding aspC was part ially sequenced. A 1179 bp ORF was identified which could encode for a 393 aa, 43.2 kDa protein. The deduced amino acid sequence had high identity to other AspC sequences in GenBank and is a member of the I gamma family of AT ases, Substrate-specificity studies suggested that the lactococcal AspC has ATase activity only with aspartic acid (Asp), An internal deletion was int roduced into the L, lactis chromosomal copy of aspC by homologous recombina tion. The wild-type and mutant strain grew similarly in defined media conta ining all 20 amino acids and did not grow in minimal media unless supplemen ted with asparagine (Asn), The mutant strain was also unable to grow in or significantly acidify milk unless supplemented with Asp or Asn, These resul ts suggest that only one lactococcal ATase is involved in the conversion of oxaloacetate to Asp, and Asp biosynthesis is required for the growth of L. lactis LM0230 in milk. Amino acid aminotransferases (ATases), which cataly se the last biosynthetic step of many amino acids, may have important physi ological functions in Lactococcus lactis during growth in milk.