Enrichments of methanotrophic-heterotrophic cultures with high poly-β-hydroxybutyrate (PHB) accumulation capacities.

Methanotrophic–heterotrophic communities were selectively enriched from sewage sludge to obtain a mixed culture with high levels of poly-β-hydroxybutyrate (PHB) accumulation capacity from methane. Methane was used as the carbon source, N2 as sole nitrogen source, and oxygen and Cu content were varied. Copper proved essential for PHB synthesis. All cultures enriched with Cu could accumulate high content of PHB (43.2%–45.9%), while only small amounts of PHB were accumulated by cultures enriched without Cu (11.9%–17.5%). Batch assays revealed that communities grown with Cu and a higher O2 content synthesized more PHB, which had a wider optimal CH4:O2 range and produced a high PHB content (48.7%) even though in the presence of N2. In all methanotrophic–heterotrophic communities, both methanotrophic and heterotrophic populations showed the ability to accumulate PHB. Although methane was added as the sole carbon source, heterotrophs dominated with abundances between 77.2% and 85.6%. All methanotrophs detected belonged to type II genera, which formed stable communities with heterotrophs of different PHB production capacities.