Hosted by: Arthur Grossman
Our recent research efforts have focused on manipulating photosynthetic and biosynthetic pathways leading to starch, triacylglycerols, medium-chain fatty acids, a suite of terpenoids, or H2 in photosynthetic microorganisms. We demonstrate that manipulation of starch biosynthetic genes in the green alga Chlamydomonas reinhardtii can increase starch accumulation at the expense of protein synthesis and cell division in nutrient replete media where starch accumulation is relatively limited. Introduction of C10 and C15 terpenoid synthases was successfully achieved in the cyanobacteria Synechocystis sp. PCC6803 and Synechococcus sp. PCC 7002 to produce, and in most cases secrete, -caryophyllene, a significant component of the oleoresin found in the “diesel tree” (Copaifera officinalis), limonene and bisabolene. We have also used thioesterase gene expression in the diatom Phaeodactylum tricornutum and Synechococcus sp. PCC 7002 to synthesize medium-chain fatty acids, which are secreted from Synechococcus sp. PCC 7002, or accumulate in the triacylglycerols of P. tricornutum. Glycogen and starch synthesis has been knocked out in Synechococcus sp. PCC 7002 and C. reinhardtii, respectively to increase metabolic substrates for lipid accumulation. In Synechococcus sp. PCC 7002, only limited increases in lipid products are observed despite the availability of metabolic precursors, which are instead secreted into the medium. In starchless mutants of C. reinhardtii, we observe modest increases in total fatty acid content, but significant increases in internal metabolites that are not being effectively captured for fatty acid synthesis. In sum, additional metabolic engineering efforts are required to fully capitalize on our current “push/pull” strategies. Photosynthetic microorganisms are in the dark for half of the diel cycle and we have conducted extensive research examining and manipulating the “dark” metabolism of C. reinhardtii, and these efforts underscore our current limitations in predicting metabolic rearrangements resulting from metabolic pathway disruption. Lastly, we are developing synthetic biology tools for the oleaginous alga Nannochloropsis gaditana, a particularly promising biofuel production strain. Genomic insights and next generation modifications to improve productivities will be presented.