Application of a Non-halogenated Solvent, Methyl Ethyl Ketone (MEK) for Recovery of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB-co-HV)] from Bacterial Cells

Conventional solvent-based methods are still the most practical approaches for recovery of polyhydroxyalkanoate (PHA) polymer from cellular biomass, even though potential alternatives exist, including chemical, mechanical, and enzymatic methods. It is still necessary, however, to avoid dangerous and environmentally unfriendly solvents (e.g., chloroform and dichloromethane) in the polymer recovery process. In the work presented here, we applied various solvent systems to recover PHA from Ralstonia eutropha and recombinant Escherichia coli cells. It was demonstrated that methyl ethyl ketone (MEK) is a promising solvent for PHA recovery from bacterial cells, particularly for the copolymer poly(hydroxybutyrate-cohydroxyvalerate) [P(HB-co-HV)], exhibiting > 90% polymer recovery. Even though MEK did not solubilize PHAs to the same extent as chloroform, it can recover a comparable amount of polymer because of its processing advantages, such as the low viscosity of the MEK/PHA solution, and the lower density of MEK as compared to cellular components. MEK was found to be the best alternative, non-halogenated solvent among examined candidates for recovery of P(HB-co-HV) from cells. The MEK treatment of PHAcontaining cells further allowed us to eliminate several costly and lengthy steps in the extraction process, such as cell lysis, centrifugation, and filtration.