Polyhydroxyalkanoates accumulation by Methylobacterium organophilum CZ-2 during methane degradation using citrate or propionate as cosubstrates

Methylobacterium organophilum CZ-2 synthesized polyhydroxyalkanoates (PHAs) under nitrogen limitation with CH₄ as carbon source and when either citrate or propionate was added as cosubstrates. The highest PHAs content (y_PHA) in closed flasks was obtained in the CH₄-citrate and CH₄-propionate experiments attaining values of 0.82 and 0.68, respectively. M. organophilum CZ-2 cultivated in bioreactors with citrate and continuous CH₄ addition yielded a final PHAs concentration of 143 g m^-3 containing hydroxybutyrate (HB), hydroxyvalerate (HV) and hydroxyoctanoate (HO), in a 55:35:10 ratio, with, y_PHA of 0.88 and a CH₄ elimination capacity (EC) of 20 g m^-3h^-1. With propionate, the y_PHA was 0.3 and the EC around 8 g m^-3h^-1. From ¹H and ¹³C NMR experiments it was found that the polymer produced with CH₄-citrate contained six different monomers: 3HB, 3HV, 4HV, 4-hydroxyheptanoate (4HH), 3HO and 4HO, showing the great versatility of this PHAs producing bacterium.