Production of Polyhydroxyalkanoates with the Fermentation of Methylorubrum extorquens Using Formate as a Carbon Substrate

Deriving both carbon and energy from formate, a single-carbon substrate, for the microbial production of value-added products allows its use as the main feedstock in biorefinery, with consequent environmental and economic benefits. Methylorubrum extorquens AM1, a strain capable of growth solely on formate, is a known producer of the biopolymer polyhydroxyalkanoate (PHA), during nitrogen-deficient growth. Based on findings from our previous report, the gene ftfL was selected for overexpression to enhance growth and PHA production using formate. Its overexpression in a poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)-producing strain yielded improved growth and a 1.4-fold increase in PHBV production. The strain could thus be tested for long-term fermentation, intended for optimized growth and production in formate. A customized fermentation regimen was established by incorporating both the conventional two-phase fermentation method for PHA production and a repeated fed-batch fermentation process designed to resolve the problem of sodium accumulation. The poly-3-hydroxybutyrate and PHBV copolymer-producing strains resulted in 11.07 g/L and 2.76 g/L of bio-degradable polymers, respectively, in the fermentation process.