(The) impacts of nitrogen and carbon resource availability on polyhydroxyalkanoate-accumulating methanotrophs from freshwater wetlands

Abstract

Aquatic environments account for half of the global methane emissions, with freshwater wetlands being the most significant contributors. Methane is oxidized by methanotrophs in soils under aerobic conditions, partially offsetting these methane fluxes. In addition, some methanotrophs can accumulate polyhydroxyalkanoate (PHA) as an energy storage molecule. In this study, we investigated how the enrichment of PHA-accumulating methanotrophic communities was affected by varying resource availability (i.e., C and N concentrations) at a fixed C/N ratio. High $CH_4$ enrichment was established from an engineering perspective while low $CH_4$ enrichment was set up based on ammonium concentrations in the natural environment. Resource availability altered C-based cell yields, suggesting the significant impacts of C resource concentrations on methanotrophic enrichments. A PHA accumulation test demonstrated that only high $CH_4$ enrichments harbored PHA-accumulating methanotrophs. 16S rRNA gene amplicon sequencing revealed that variable nutrient-supplying conditions influenced microbial community compositions and diversity. The Methylocystis genus was dominant in the high $CH_4$ enrichment leading to a less diverse microbial community, whereas higher diversity was observed in the low $CH_4$ enrichment.