Intracellular PHB conversion in a Type II methanotroph studied by (13)C NMR.

Poly-beta-hydroxybutyrate (PHB) formation under aerobic conditions via incorporation of [(13)C-2]acetate as a cosubstrate and its intracellular degradation under anaerobic conditions in a Type II methanotroph was studied by (13)C NMR. During PHB synthesis in the presence of labelled acetate, low levels of beta-hydroxybutyrate, butyrate, acetone, isopropanol, 2,3-butanediol and succinate were observed. Subsequent anaerobic PHB breakdown showed enhanced levels of these products at the expense of PHB. Fermentative metabolism occurring during anaerobic PHB degradation was confirmed in experiments with fully (13)C-enriched cells, which were grown on (13)C-labelled methane. beta-hydroxybutyrate, butyrate, acetate, acetone, isopropanol, 2,3-butanediol and succinate were detected as multiple (13)C-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.