Physiological effects of starchless mutations, sta6 (BAFJ5) and sta7-10, on metabolic carbon partitioning in Chlamydomonas reinhardtii
Robert E. Jinkerson1, Victoria H. Work2, Randor Radakovits1, Jonathan E. Meuser2, Lee G. Elliott2, and Matthew C. Posewitz1
1) Department of Chemistry & Geochemistry, Colorado School of Mines, Golden, CO 80401, USA
2) Division of Environmental Science and Engineering, Colorado School of Mines, 1500 Illinois St., Golden, Colorado 80401, USA
Phototrophic microorganisms (PSMs) are capable of efficiently converting sunlight, CO2, and water into a diverse array of renewable bioenegy carriers. Moreover, PSMs are able to grow in diverse environments, such as salt water and industrial waste streams, and do not accumulate large quantities of recalcitrant biomass, such as lignin and cellulose. Despite these positive attributes, significant challenges remain prior to using PSMs in an economically viable biofuel process. Neither photon conversion efficiencies, nor metabolic pathways, are currently optimized for anthropologic energy production. Carbon is partitioned between the two predominate energy storage molecules, starch and lipids, and despite the significance of these molecules the metabolic, enzymatic, and regulatory mechanisms controlling the partitioning of metabolites into these distinct carbon stores are poorly understood in algae. We investigated Chlamydomonas reinhardtii mutants with disrupted starch synthesizing enzymes, sta6 (ADP-glucose pyrophosphorylase) and sta7 (isoamylase), and two complemented strains of sta7. When these starch synthesizing enzymes are disrupted a starch-less phenotype results with increased lipid content, decreased acetate utilization, altered growth rates and decreased photosynthetic oxygen evolution compared to a control strain, CC124. This decrease in overall anabolic processes is in stark contrast to the complemented strains of sta7 which produce greater quantities of cellular starch and lipid than CC124, in both nitrogen replete and deplete medium.
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