Enhancement of Poly(β-hydroxybutyrate) Production from Methanol by Methylobacterium Extorquens Using Mixed Substrates

Poly-β-hydroxybutyrate (PHB), produced by several species of bacteria, hasattracted great attention as a biodegradable and biocompatible compoundwith almost similar properties of polypropylene. Unfortunately, its use iscurrently limited due to high production costs. One of the most common methods forovercoming this constraint is the use of inexpensive substrates, like methanol.Another strategy which involves the increase in carbon yield which can directlyaffect the production costs. One method to increase carbon yield is the use of mixedsubstrates. Therefore, for PHB production the effects of three sources of carbon,ethanol, sodium acetate, and glucose were studied as substrates in different concentrations mixed with methanol. It was found that PHB concentration and PHB content increased by addition of ethanol and acetate, but glucose addition did not have any significant effect on PHB production. Calculation of carbon yield under the best condition indicated that it increased about 3 times by addition of acetate