Microbial Conversion of Methane into poly-β-hydroxybutyrate (PHB): Growth and intracellular product accumulation in a type II methanotroph

Abstract

The biochemical pathways of methane to poly-β-hydroxybutyrate (PHB) in type II methanotrophs have been analyzed and used to propose stoichiometric equations for cell biomass and PHB. Conditions necessary for PHB accumulation in a batch culture of Methylocystis parvus OBBP were studied. In nitrogen limited cultures PHB started accumulating in the declining growth phase and maximum rate of PHB formation occurred during the late growth and early stationary phases. Inoculum age had an effect on maximum level of intracellular PHB, which increased with inoculum age up to ca. 70% of the cell dry weight using a 70 h inoculum. It has been shown that oxygen and methane requirements are high and pose a great stress on the mass transfer in the system; this limits the obtainment of high cell concentrations. When conditions for increased mass transfer of both CH 4 and O 2 were used, 5 g/ l of cells could be produced. Finally an enrichment strategy was investigated so that cells would start accumulating PHB earlier during the growth phase. Alternatives to increase cell mass concentrations are discussed.