The present study shows that the formation of AABA is widely distributed within P. acidilactici species. To our knowledge, this has not been reported for other LAB species. Additionally, all P. acidilactici strains produced alanine and degraded serine and threonine in vitro, suggesting the two latter amino acids are the precursors for the alanine and AABA formation. The purified recombinant aminotransferase Aat was active under conditions encountered in a cheese environment (pH 5.5, elevated salt concentrations). The study of the functional involvement of Aat in the in vivo AABA metabolism of P. acidilactici is currently ongoing. The unreduced growth rate of the knockout strain in MRS broth indicates that aat is not essential for the growth of P. acidilactici. Further broth based and eventually cheese experiments will be performed to reveal the role of Aat in the in situ formation of AABA.
