Producing poly-3-hydroxybutyrate with a high molecular mass from methane

Poly-3-hydroxybutyrate (PHB) and other polyesters can be produced by variou s species of bacteria. Of the possible carbon sources, methane could provid e a suitable substrate for the production of PHB. Methane is cheap and plen tiful - not only as natural gas, but also as biogas. The methanotrophic str ain Methylocystis sp. GB 25 DSMZ 7674 is able to accumulate PHB in a brief non-sterile process. The studies were carried out using a 7-1 and a 70-1 pr essure bioreactor. Cultivation was performed in two stages: a continuous gr owth phase (dilution rate 0.17 h(-1)) and a PHB accumulation phase under de ficiency conditions of an essential nutrient (ammonium, phosphorus or magne sium) in batch culture. The PHB content of biomass was as high as 51%; effi ciency was highest during the first 5 h of the product formation process. T he maximum PHB yield relative to the methane consumed was estimated to be 0 .55 g g(-1). The PHB produced is of very high quality, having a high molecu lar mass of up to 2.5 x 10(6) Da. (C) 2001 Elsevier Science B.V. All rights reserved.