Biosynthesis pathway of flavor compound 3-methylbutanal derived from leucine by Lactococcus lactis 517: From a transcriptomics perspective

This study aimed to investigate the synthesis mechanism of 3-methylbutanal derived from leucine (Leu) by Lactococcus lactis 517 through changes in gene expression. The production of 3-methylbutanal was evaluated during 72 h of incubation using three models, including M17+L. lactis 517, M17+Leu + L. lactis 517, and PBS + Leu + L. lactis 517. The PBS model exhibited the highest level of 3-methylbutanal (434.50 μM) and was employed to explore the pathway of 3-methylbutanal formation by transcriptomic analysis at different time points (0, 6, and 48 h). A total of 1973 genes were detected in L. lactis 517, among which 433 differential genes were identified. Gene ontology and Kyoto encyclopedia of genes and genomes enrichment analysis showed that differential genes mainly involved small molecule catabolism, organonitrogen compound catabolism, proteolysis, lysine biosynthesis, glycolysis, and pentose phosphate pathway. Several key differential genes related to the synthesis of 3-methylbutanal, including ilvE, kdcA, pdhA, pdhB, pdhC, pdhD, pta, ackA, and adh. The inhibition of α-keto acid dehydrogenase (KADH) activity by adding sodium arsenite resulted in a 15.30% decrease in the concentration of 3-methylbutanal. Our data suggest that the synthesis of 3-methylbutanal derived from Leu by L. lactis 517 primarily involves direct decarboxylation by α-keto acid decarboxylase, assisted by the KADH complex.