Identification of a tyrosine decarboxylase gene (tdcA) in Streptococcus thermophilus 1TT45 and analysis of its expression and tyramine production in milk.

In this study, a tyrosine decarboxylase gene (tdcA) was identified in 1 among 83 Streptococcus thermophilus strains tested. Its sequence, nearly identical to that of a tdcA of Lactobacillus curvatus, indicated a horizontal gene transfer event. Transcription in milk and the formation of critical levels of tyramine were observed in the presence of tyrosine