The aminotransferase Aat initiates 3-phenyllactic acid biosynthesis in Pediococcus acidilactici .

The function of the aminotransferase Aat (GenBank Protein WP_159211138) from FAM 18098 was studied . For this purpose, the gene was replaced with an erythromycin resistance gene using the temperature-sensitive shuttle plasmid pSET4T_Δ. The knockout was verified by PCR and genome sequencing. Subsequently, the differences between the metabolism of the knockout and of the wild-type strain were investigated by determining the free amino acids and organic acids in culture supernatants. It was found that the knockout mutant no longer synthesized 3-phenyllactic acid (PLA) and 4-hydroxyphenyllactic acid (HPLA). Additionally, the mutant strain no longer catabolized phenylalanine. Metabolic pathway analysis using the KEGG database indicate that cannot synthesize α-ketoglutarate that is a predominant amino-group acceptor in many transamination reactions. To study the transfer of the amino group of phenylalanine, the wild-type strain was incubated with [N] phenylalanine. Mass spectrometry showed that during fermentation, [N] alanine was formed, indicating that pyruvic acid is an amino group acceptor in . The present study shows that Aat plays a crucial role in PLA/HPLA biosynthesis and pyruvic acid is an amino acceptor in transamination reactions in .