4-04: Lipid production in Rhodobacter sphaeroides: from photosynthetic membranes to biofuels

Rhodobacter sphaeroides is a facultative bacterium that can grow via aerobic or anaerobic respiration, photosynthesis, or fermentation. Under low oxygen and anaerobic conditions R. sphaeroides develops invaginations of the cytoplasmic membrane, called intracytoplasmic membranes (ICM), which increase its membrane surface area and allow for synthesis of the photosynthetic apparatus that harvests light energy. We are using this physiologic increase in phospholipid membrane under anaerobic conditions to investigate the underlying increase in fatty acid biosynthesis and its regulatory mechanisms. Here we show that total fatty acid content increases by 3-4 times per cell under low oxygen and anaerobic growth conditions. We have found that anaerobic induction of lipid synthesis is dependent on multiple regulatory pathways that collaborate to induce photosynthetic capabilities of the bacterium, yet none of them alone are capable of inducing increased lipid production. To identify other gene products that may induce anaerobic lipid production, we have performed a genome-wide screen, using the lipophilic dye Nile Red, for mutations that increase lipid production under aerobic growth conditions. Several such lesions have been identified, and we are currently investigating how these gene products impinge on membrane lipid accumulation. Once characterized, these regulatory mechanisms will be used to increase fatty acid production in this and other microbial systems for the production of commercially relevant lipid products. These studies will provide critical insight into the regulation and requirements of bacterial lipid biosynthesis and accumulation; knowledge that will be critical for the engineering of this and/or other microorganisms for large-scale biological oil production.