P8: Effects of culture conditions on microbial lipid accumulation in the batch cultivation of Methylomicrobium sp. with methane as sole carbon source

Methanotrophs have been utilized for bioremediation and biocatalysis for decades due to the versatile enzyme, methane monooxygenase (MMO). This enzyme catalyzes the first step in methanotrophy, the controlled oxidation of methane to methanol and allows the methanotroph to utilize methane as both carbon and energy source.  Methanotrophic bacteria have the ability to convert methane to all cellular components and thus have the potential to serve as a production platform for the conversion of methane into valuable products including biofuels via lipid biosynthetic pathways and catalytic hydrodeoxygenation upgrading. Because of the relatively low price of natural gas and increasing demands of liquid transportation fuels, attention has begun to turn to methanotrophic bacteria for biofuel production. In this study, the optimal conditions for cell growth and production of lipids were determined in batch cultivation of a mutantMethylomicrobium sp. in bottle cultures. Plackett–Burman design was applied to optimize the culture medium composition for higher cell density and lipid concentration with CH₄ as sole carbon source. The influence of MMO related trace elements on lipid production was also investigated. Through Box-Behnken design and response surface methodology, the optimal culture temperature, pH, and nitrogen source were investigated for improving lipid yield from CH₄. Temperatures ranging from 20-35⁰C and pH values from 7-11 were tested in the study. Nitrate, ammonia, urea, and glycine were also explored in batch cultures. By using the optimal culture conditions and modified culture medium, cell density, lipid concentration, and lipid yield on CH₄ were maximized.