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(-3)h(-1). With propionate, the y(PHA) was 0.3 and the EC around 8 g m(-3)h(-1). From H-1 and C-13 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. (C) 2012 Elsevier Ltd. All rights reserved.