Production of gamma-aminobutyric acid by Escherichia coli using glycerol as a sole carbon source

BACKGROUND: In the biodiesel industry, crude glycerol is produced in huge quantities as a by-product, and therefore, the economic conversion of crude glycerol into a value-added product is a priority. One possible way of achieving such a conversion is to feed glycerol to Escherichia coli cells so that they can grow and produce valuable products such as gamma-aminobutyric acid (GABA) at the same time. RESULTS: Four E. coli strains were compared for their growth rates and GABA production using glycerol as sole carbon source. GABA production was associated with cell growth by constitutively expressed mutant glutamate decarboxylase that exhibited activity at neutral pH. Simple treatment of crude glycerol with phosphoric acid resulted in a fermentable grade of glycerol, and the superb strain, W, converted 2.0 g L⁻¹ of crude glycerol into 0.15 g L⁻¹ of GABA in 12 h in a batch culture. In a fed-batch type culture with pH titration, the strain W converted overall 15 g L⁻¹ of crude glycerol into 0.98 g L⁻¹ of GABA in 36 h. CONCLUSION: It is possible to convert crude glycerol into GABA in a growth-associated manner using E. coli W, and the strain will serve as a base strain for future metabolic engineering approaches.