Biosynthesis of polyhydroxybutyrate from methane and carbon dioxide using type II methanotrophs.

Methane (CH) and carbon dioxide (CO) are the dominant greenhouse gases (GHGs) that are increasing at an alarming rate. Methanotrophs have emerged as potential CH and CO biorefineries. This study demonstrated the synchronous incorporation of CH and CO into polyhydroxybutyrate (PHB) for the first time using C-labeling experiments in methanotrophs. By supplying substantial amounts of CO, PHB content was enhanced in all investigated type II methanotrophic strains by 140 %, 146 %, and 162 %. The highest content of PHB from CH and CO in flask-scale cultivation reached 38 % dry cell weight in Methylocystis sp. MJC1, in which carbon percentage in PHB from CO was 45 %. Flux balance analysis predicted the critical roles of crotonyl-CoA carboxylase/reductase and phosphoenolpyruvate carboxylase in CO recycling. This study provided proof of the conversion of GHGs into a valuable and practical product using methanotrophic bacteria, contributing to addressing GHG emissions.