Resource availability governs polyhydroxyalkanoate (PHA) accumulation and diversity of methanotrophic enrichments from wetlands

Abstract

<jats:p>Aquatic environments account for half of global CH<jats:sub>4</jats:sub> emissions, with freshwater wetlands being the most significant contributors. These CH<jats:sub>4</jats:sub> fluxes can be partially offset by aerobic CH<jats:sub>4</jats:sub> oxidation driven by methanotrophs. Additionally, some methanotrophs can convert CH<jats:sub>4</jats:sub> into polyhydroxyalkanoate (PHA), an energy storage molecule as well as a promising bioplastic polymer. In this study, we investigate how PHA-accumulating methanotrophic communities enriched from wetlands were shaped by varying resource availability (i.e., C and N concentrations) at a fixed C/N ratio. Cell yields, PHA accumulation, and community composition were evaluated in high (20% CH<jats:sub>4</jats:sub> and 10 mM NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup>) and low resource (0.2% CH<jats:sub>4</jats:sub> and 0.1 mM NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup>) conditions simulating engineered and environmental settings, respectively. High resource availability decreased C-based cell yields, while N-based cell yields remained stable, suggesting nutrient exchange patterns differed between methanotrophic communities at different resource concentrations. PHA accumulation was only observed in high resource enrichments, producing approximately 12.6% ± 2.4% (m/m) PHA, while PHA in low resource enrichments remained below detection. High resource enrichments were dominated by <jats:italic>Methylocystis</jats:italic> methanotrophs, while low resource enrichments remained significantly more diverse and contained only a minor population of methanotrophs. This study demonstrates that resource concentration shapes PHA-accumulating methanotrophic communities. Together, this provides useful information to leverage such communities in engineering settings as well as to begin understanding their role in the environment.</jats:p>