Isoprene production in Synechocystis under alkaline and saline growth conditions

Photosynthesis for the generation of isoprene in cyanobacteria was demonstrated with Synechocystis, entailing a process where a single host microorganism acts as both photocatalyst and processor, photosynthesizing and emitting isoprene hydrocarbons. A practical aspect of the commercial exploitation of this process in mass culture is the need to prevent invading microorganisms that might cause a culture to crash, and to provide an alternative to freshwater in scale-up applications. Growth media poised at alkaline pH are desirable in this respect, as high pH might favor the growth of the cyanobacteria, while at the same time discouraging the growth of invading predatory microbes and grazers. In addition, demonstration of salinity tolerance would enable the use of seawater for cyanobacteria cultivations. However, it is not known if Synechocystis growth and the isoprene-producing metabolism can be retained under such theoretically non-physiological conditions. We applied the gaseous/aqueous two-phase photobioreactor system with Synechocystis transformed with the isoprene synthase gene (SkIspS) of Pueraria montana (kudzu). Rates of growth and isoprene production are reported under control, and a combination of alkalinity and salinity conditions. The results showed that alkalinity and salinity do not exert a negative effect on either cell growth or isoprene production rate and yield in Synechocystis. The work points to a practical approach in the design of cyanobacterial growth media for applications in commercial scale-up and isoprene production.