An Engineered Methanogenic Pathway Derived from the Domains Bacteria and Archaea

A plasmid-based expression system wherein mekB was fused to a constitutive Methanosarcina acetivorans promoter was used to express MekB, a broad-specificity esterase from Pseudomonas veronii, in M. acetivorans. The engineered strain had 80-fold greater esterase activity than wild-type M. acetivorans. Methyl acetate and methyl propionate esters served as the sole carbon and energy sources, resulting in robust growth and methane formation, with consumption of >97% of the substrates. Methanol was undetectable at the end of growth with methyl acetate, whereas acetate accumulated, a result consistent with methanol as the more favorable substrate. Acetate was consumed, and growth continued after a period of adaptation. Similar results were obtained with methyl propionate, except propionate was not metabolized.