Intracellular PHB conversion in a Type II methanotroph studied by C-13 NMR

Poly-beta -hydroxybutyrate (PHB) formation under aerobic conditions via inc orporation of [C-13-2]acetate as a cosubstrate and its intracellular degrad ation under anaerobic conditions in a Type II methanotroph was studied by C -13 NMR. During PHB synthesis in the presence of labelled acetate, low leve ls of beta -hydroxybutyrate, butyrate, acetone, isopropanol, 2,3-butanediol and succinate were observed. Subsequent anaerobic PHB breakdown showed enh anced levels of these products at the expense of PHB. Fermentative metaboli sm occurring during anaerobic pHD degradation was confirmed in experiments with fully C-13-enriched cells, which were grown on C-13-labelled methane. beta -hydroxybutyrate, butyrate, acetate, acetone, isopropanol, 2,3-butaned iol and succinate were detected as multiple C-13-labelled compounds in the culture medium. Our results suggest that intracellular PHB degradation can be used as a reserve energy source by methanotrophs under anoxic conditions .