Sequencing of the Tyrosine Decarboxylase Cluster of Lactococcus lactis IPLA 655 and the Development of a PCR Method for Detecting Tyrosine Decarboxylating Lactic Acid Bacteria

Abstract

The enzymatic decarboxylation of tyrosine produces tyramine, the most abundant biogenic amine in dairy products—especially in cheeses. The screening of lactic acid bacteria isolated from different artisanal cheeses and a number of microbial collections identified 22 tyramine-producing strains belonging to different genera. The Lactococcus lactis strain IPLA 655 was selected, and the genes encoding a putative tyrosyl tRNA synthetase, a tyrosine decarboxylase (tdcA), and a tyrosine-tyramine antiporter, found together as a cluster, were sequenced. The disruption of tdcA yielded a strain unable to produce tyramine. Comparison of the L. lactis IPLA 655 tdcA gene with database tdcA sequences led to the design of two primers for use in a PCR method that identified potential tyramine-producing strains. The proposed method can use purified DNA, isolated colonies, milk, curd, and even cheese as a template. Molecular tools for the rapid detection of tyramine-producing bacteria at any time during the fermentation process could help prevent tyramine accumulation in fermented foods. The proposed technique could be of great use to the food industry.