Promoter engineering for microbial bio-alkane gas production

Successful industrial biotechnological solutions to biofuels and other chemicals production rely on effective competition with existing lower-cost natural sources and synthetic chemistry approaches enabled by adopting low-cost bioreactors and processes. This is achievable by mobilizing Halomonas as a next generation industrial chassis, which can be cultivated under non-sterile conditions. To increase the cost effectiveness of an existing sustainable low carbon bio-propane production strategy, we designed and screened a constitutive promoter library based on the known strong porin promoter from Halomonas. Comparative studies were performed between Escherichia coli and Halomonas using the reporter gene red fluorescent protein (RFP). Later studies with a fatty acid photodecarboxylase-RFP fusion protein demonstrated tuneable propane production in Halomonas and E. coli, with an ∼8-fold improvement in yield over comparable isopropyl-β-D-thiogalactoside-inducible systems. This novel set of promoters is a useful addition to the synthetic biology toolbox for future engineering of Halomonas to make chemicals and fuels.