Enhanced accumulation of γ-aminobutyric acid by deletion of aminotransferase genes involved in γ-aminobutyric acid catabolism in engineered <i>Halomonas elongata</i>

In this study, we were able to increase the yield of GABA by 1.5 times in the GABA-producing <i>H. elongata</i> ZN3 strain by deleting the <i>gabT</i> gene, which encodes GABA-AT, the initial enzyme of the GABA catabolic pathway. We also report the first <i>in vivo</i> evidence for GABA aminotransferase activity of an <i>ectB</i>-encoded DABA-AT, confirming a longstanding speculation based on the reported <i>in vitro</i> GABA-AT activity of DABA-AT. According to our findings, the DABA-AT enzyme can catalyze the initial step of GABA catabolism, in addition to its known function in ectoine biosynthesis. This creates a cycle that promotes adequate substrate flow between the two pathways, particularly during the early stages of high-salinity stress response when the expression of the <i>ectB</i> gene is upregulated.