Polyhydroxybutyrate Production from Methane and Carbon Dioxide by a Syntrophic Consortium of Methanotrophs with Oxygenic Photogranules without an External Oxygen Supply

Here, a syntrophic process was developed to produce polyhydroxy-beta-butyrate (PHB) from a gas stream containing CH4 and CO2 without an external oxygen supply using a combination of methanotrophs with the community of oxygenic photogranules (OPGs). The co-culture features of Methylomonas sp. DH-1 and Methylosinus trichosporium OB3b were evaluated under carbon-rich and carbon-lean conditions. The critical role of O-2 in the syntrophy was confirmed through the sequencing of 16S rRNA gene fragments. Based on their carbon consumption rates and the adaptation to a poor environment, M. trichosporium OB3b with OPGs was selected for methane conversion and PHB production. Nitrogen limitation stimulated PHB accumulation in the methanotroph but hindered the growth of the syntrophic consortium. At 2.9 mM of the nitrogen source, 1.13 g/L of biomass and 83.0 mg/L of PHB could be obtained from simulated biogas. These results demonstrate that syntrophy has the potential to convert greenhouse gases into valuable products efficiently.

Automated summary

A syntrophic process utilizing methanotrophs and oxygenic photogranules (OPGs) was developed to produce polyhydroxy-beta-butyrate (PHB) from a gas stream containing CH4 and CO2 without external oxygen supply. The role of O2 in the synergy was confirmed and M. trichosporium OB3b with OPGs was selected for methane conversion and PHB production. Nitrogen limitation stimulated PHB accumulation in methanotrophs but hindered the growth of the syntrophic consortium. Under a nitrogen source concentration of 2.9 mM, 1.13 g/L of biomass and 83.0 mg/L of PHB could be obtained from simulated biogas. These results demonstrate the efficient conversion of greenhouse gases into valuable products through syntrophy.