Production and characterization of a biodegradable polymer, poly (3-hydroxybutyrate-co-3-hydroxyvalerate), using the type II methanotroph, Methylocystis sp. MJC1

The production of polyhydroxyalkanoates (PHAs) through the biological conversion of methane is a promising solution to address both methane emissions and plastic waste. Type II methanotrophs naturally accumulate a representative PHA, poly(3-hydroxybutyrate) (PHB), using methane as the sole carbon source. In this study, we aimed to produce poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV copolymer) with improved properties compared with PHB, using the type II methanotroph, Methylocystis sp. MJC1. We optimized the pH, valerate concentration, and valerate supply time in a one-step cultivation process using a gas bioreactor to enhance PHBV copolymer production yield and the 3-hydroxyvalerate (3HV) molar fraction. Under the optimal conditions, the biomass reached 21.3 g DCW/L, and PHBV copolymer accumulation accounted for 41.9 % of the dried cell weight, with a 3HV molar fraction of 28.4 %. The physicochemical properties of the purified PHBV copolymer were characterized using NMR, FTIR, TGA, DSC, and GPC.

Automated summary

The production of polyhydroxyalkanoates (PHAs) through the biological conversion of methane offers a promising solution for addressing methane emissions and plastic waste. This study successfully produced poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV copolymer) with improved properties compared to poly(3-hydroxybutyrate) (PHB), using the type II methanotroph, Methylocystis sp. MJC1. Optimization of cultivation conditions resulted in high PHBV copolymer yield and 3-hydroxyvalerate (3HV) molar fraction.