Efficient production of gamma-aminobutyric acid by engineeredSaccharomyces cerevisiaewith glutamate decarboxylases fromStreptomyces

Gamma-aminobutyric acid (GABA) is an industrially valuable natural product. This study was aimed to establish an efficient food-grade production process of GABA by engineeringSaccharomyces cerevisiaethat is generally recognized as safe (GRAS). GABA can be produced by catalytic decarboxylation ofl-glutamate (l-Glu) by glutamate decarboxylase (GAD, EC4.1.1.15). Two GADs, SsGAD fromStreptomyces sp. MJ654-NF4 and ScGAD fromStreptomyces chromofuscusATCC 49982, were heterologously expressed inS. cerevisiaeBJ5464. The engineered yeast strains were used as whole-cell biocatalysts for GABA production.S. cerevisiaeBJ5464/SsGAD exhibited significantly higher efficient catalytic activity than that ofS. cerevisiaeBJ5464/ScGAD. The optimal bioconversion system consisted of a cell density of OD(600)30, 0.1 Ml-Glu, and 0.28 mM pyridoxal phosphate in 0.2 M Na2HPO4-citric acid buffer with pH 5.4, and the reactions were performed at 50 degrees C for 12 H.S. cerevisiaeBJ5464/SsGAD cells can be reused, and the accumulated GABA titer reached 62.6 g/L after 10 batches with an overall molar conversion rate of 60.8 mol%. This work thus provides an effective production process of GABA using engineered yeast for food and pharmaceutical applications.