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Studies on Lipid Metabolism under Nutrient Limitation in Microalgae, Chlorella sorokiniana

Jithesh Vijayan, University of Nebraska - Lincoln


In the past two decades algal biofuels have emerged as a promising source of renewable energy. Algal biofuels can be of different forms including hydrogen, oil based biodiesel and starch based ethanol. Although some strides have been made in developing algae as a reliable source of oil, much is still to be done. One of the primary obstacle in this is the lack of understanding of the underlying mechanisms. Works reported in this thesis aids in furthering of our knowledge on how microalgae accumulate oil under nutrient limitation. To that extend, roles of two signaling systems, Reactive Oxygen Species (ROS) and Target Of Rapamycin (TOR), in Chlorella sorokiniana under nitrogen limitation are presented. Under nitrogen limitation C. sorokiniana accumulates ROS by downregulating the scavenging mechanism and actively increasing the synthesis. This increase in ROS level induces the degradation of monogalactosyldiacylglycerol, a plastidial lipid. Fatty acid from MDGD is channeled to oil biosynthesis. This in turn leads to chlorosis, degreening of cells. Chapter 3 details how TOR signaling is affected under nitrogen limitation and this leads to a reduction in fatty acid synthesis, an essential substrate for synthesis of glycerolipids including oil. Downregulation of fatty acid synthesis under nitrogen limitation is by transcriptional control of key enzymes involved in the process, namely Acetyl-CoA Carboxylase and Fatty Acid Synthase. TOR mediated downregulation of fatty acid synthesis under nitrogen limitation is common to C. sorokiniana and Chlamydomonas reinhardtii, a model organism in algal research. Chapter 4 presents a comparative analysis of nitrogen and phosphorus limitation in C. sorokiniana using a transcriptomic approach. Both conditions accumulate oil to varying levels. ROS accumulation is specific to nitrogen limitation and therefore chlorosis occurs only in nitrogen limitation not under phosphorus limitation. Nitrogen limitation induces an early growth arrest while phosphorus limitation does not. This provides a new avenue to explore and and for biotechnological intervention to produce more oil in C. sorokiniana.

Subject Area

Biology|Plant sciences|Biochemistry

Recommended Citation

Vijayan, Jithesh, "Studies on Lipid Metabolism under Nutrient Limitation in Microalgae, Chlorella sorokiniana" (2019). ETD collection for University of Nebraska-Lincoln. AAI27667280.