The glutamate dehydrogenase (GDH) catalyses the reversible conversion of glutamate into α-ketoglutarate, which initiates amino acid transamination during cheese ripening. This work has investigated the GDH activity in 39 wild isolates of Lactococcus lactis from raw milk cheeses. Only 25% of the isolates were GDH positive with NAD as the preferred cofactor. L. lactis IFPL953 showed the highest NAD-GDH activity. The GDH activity at the genetic level in the lactococcal isolates was analysed by PCR amplification of the gdh gene in genomic and plasmid DNA. The gdh gene arrangement of L. lactis IFPL953 in its plasmid location was similar to that in the reference strain GDHL. lactis TiL504, suggesting that both lactococci could harbour the same plasmid pGdh442 containing the gdh gene. L. lactis IFPL953 has previously demonstrated a remarkable α-ketoisovalerate decarboxylase activity, which along with its high GDH activity makes the strain particularly useful in enhancing cheese flavour formation.

The authors acknowledge the funding from the Spanish MINEICO (AGL2012-35814, AGL2016-75951-R and P916PTE0233).

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