Construction of a cyanobacterium synthesizing cyclopropane fatty acids

Microalgae have received much attention as a next-generation source of biomass energy. However, most of the fatty acids (FAs) from microalgae are multiply unsaturated; thus, the biofuels derived from them are fluid, but vulnerable to oxidation. In this study, we attempted to synthesize cyclopropane FAs in the cyanobacterium Synechocystis sp. PCC 6803 by expressing the cfa gene for cyclopropane FA synthase from Escherichia coli with the aim of producing FAs that are fluid and stable in response to oxidization. We successfully synthesized cyclopropane FAs in Synechocystis with a yield of ~ 30% of total FAs. Growth of the transformants was altered, particularly at low temperatures, but photosynthesis and respiration were not significantly affected. C16:1∆ 9 synthesis in the desA−/desD− strain by expression of the desC2 gene for sn-2 specific ∆ 9 desaturase positively affected growth at low temperatures via promotion of various cellular processes, with the exceptions of photosynthesis and respiration. Estimation of the apparent activities of desaturases suggested that some acyl-lipid desaturases might recognize the lipid side chain.