Abstract
Biosynthesis of poly-3-hydroxybutyrate (PHB) by Methylocystis hirsuta from natural gas in two different media was studied for the first time. After selection of the suitable medium, the effect of two key parameters such as methane to air ratio and nitrogen content on the PHB production was determined in a bubble column bioreactor using a full factorial design. It was found that both of these factors had a significant effect on the PHB accumulation (42.5% w/w of cell dry weight). PHB production by M. hirsuta, unlike other methanotrophic bacteria, was found to be a growth associated metabolite. Subsequently, the PHB production was carried out in a forced-liquid vertical tubular loop bioreactor (VTLB) at optimum condition determined in the bubble column bioreactor. The PHB content of biomass was 51.6% w/w of cell dry weight (CDW) in the VTLB. These results indicated that the loop bioreactors specially are suitable candidates for PHB production from natural gas.