Expression of glr gene encoding glutamate racemase in Bacillus licheniformis WX-02 and its regulatory effects on synthesis of poly-γ-glutamic acid

The glr gene, which encodes glutamate racemase involved in the conversion of l-glutamic acid to its D-isomer, was cloned and expressed in Bacillus licheniformis WX-02. Overexpression of the glr gene not only increased the production of poly-gamma-glutamic acid (gamma-PGA) by 22.5% but also increased the proportion of d-glutamate in gamma-PGA from 77 to 85%. The activity of glutamate racemase was higher than in the original strain throughout cultivation. This is the first report that overexpression of the glr gene could enhance the l- and d-glutamate conversion in B. licheniformis WX-02 and increase the proportion of d-glutamate in gamma-PGA and the yield of gamma-PGA.