S135: Photons to Fuels: Metabolic Pathway Manipulation for Starch, Oils or Hydrogen in Photosynthetic Microorganisms

Photosynthetic microorganisms are able to synthesize a portfolio of renewable energy carriers which can alleviate the concerns associated with fossil energy utilization. Our research efforts have focused on manipulating biosynthetic pathways leading to starch, triacylglycerols, fatty acid secretion, isoprenes or hydrogen gas. Recent advances in each of these fronts will be presented. We demonstrate that manipulation of the starch biosynthetic genes in Chlamydomonas reinhardtii significantly increases starch accumulation at the expense of protein synthesis and cell growth. Importantly, this phenotype occurs in nutrient replete medium and does not significantly compromise photosynthetic efficiencies under laboratory culturing conditions.  This is contrast to our observations using “push” approaches, which often attenuate oxygen evolution. We have also used thioesterase gene expression in the diatom Phaeodactylum tricornutum as a proof of principle to demonstrate that shorter chain fatty acids accumulate in the lipid bodies of this phototroph.  Thioesterase expression enables fatty acid secretion from Synechococcus sp. PCC 7002. Manipulation of the isoprene biosynthetic pathway has been successfully achieved in the cyanobacterium Synechocystis sp. PCC6803 and Synechococcus sp. PCC 7002 to produce b-caryophyllene, a significant component of the oleoresin found in the “diesel tree”, Copaifera officinalis. Isolated knockouts in both of the hydrogenase genes in Chlamydomonas reinhardtii have been attained and mechanisms to integrate hydrogen and carbon metabolisms in this alga will be discussed. Lastly, we sequenced and developed transformation protocols for the oleaginous alga Nannochloropsis gaditana, a particularly promising production strain. Genomic insights and next generation modifications to improve productivities will be presented.