Production of 4-hydroxybutyric acid by metabolically engineered Mannheimia succiniciproducens and its conversion to γ-butyrolactone by acid treatment

γ-Butyrolactone (GBL) is an important four carbon (C4) chemical, which has a wide range of industrial applications. GBL can be produced by acid treatment of 4-hydroxybutyric acid (4-HB), which is a derivative of succinic acid. Heterologous metabolic pathways were designed and established in succinic acid overproducing Mannheimia succiniciproducens LPK7 (ldhA pflD pta ackA mutant) by the introduction of heterologous genes that encode succinyl-CoA synthetase, CoA-dependent succinate semialdehyde dehydrogenase, and either 4-hydroxybutyrate dehydrogenase in LPK7 (p3S4CD) or succinate semialdehyde reductase in LPK7 (p3SYCD). Fed-batch cultures of LPK7 (p3S4CD) and LPK7 (p3SYCD) resulted in the production of 6.37 and 6.34 g/L of 4-HB (molar yields of 0.143 and 0.139), respectively. Finally, GBL was produced by acid treatment of the 4-HB obtained from the fermentation broth with molar yield of 0.673. This study demonstrates that 4-HB, and potentially other four carbon platform chemicals, can be produced by the engineered rumen bacterium M. succiniciproducens.