A Three‐Pronged Synergistic Approach to Increase the Biofeedstock Viability of Chlorella vulgaris

Abstract

Over the last several decades, the global temperature has increased at an alarming rate, increasing the need for efficient renewable energy sources. 1 Microalgae are a promising source of biodiesel due to their high rate of lipid accumulation, but are not efficient enough to produce biofuel on a scale matching current fuel needs. 2Chlorella vulgaris is a fast‐growing unicellular green microalga with a high percent of lipids per biomass, making it a promising candidate for biodiesel production. Previous research has used two approaches to increase the accumulation of lipids and photosynthetic activity: the addition of exogenous glycerol or the addition of excess Mn2+. When used separately, the addition of glycerol increases neutral lipid production in C. vulgaris while the addition of Mn2+ increases photosynthetic capacity. 3 Glycerol was found to be directly incorporated into the triacylglycerol (TAG) backbone, which allowed for an increased flux toward TAG synthesis without significantly changing the energy exerted. Manganese was shown to increase the rate of electron transfer through photosystem II, increasing the overall photosynthetic output. While it was assumed that combining these conditions would further optimize the cultures for lipid production, this was not the case: when used simultaneously, they decrease TAG production. To improve lipid productivity, a three‐pronged synergistic approach was taken combining Mn2+‐replete conditions, nitrogen deprivation, and exogenous glycerol. Nitrogen was deprived from the cells, because under nitrogen deplete conditions cells shift away from protein synthesis and towards energy storage compounds that can be used to produce TAGs. Cultures were then monitored for turbidity, chlorophyll content, lipid productivity, biomass, and TAG content. Cells grown using this three‐pronged approach showed an increase in the amount of TAGs produced over time as the glycerol concentrations were increased. This novel approach can be used to increase lipid synthesis to increase biofuel feasibility.Support or Funding Information#NNX15AI01H.D.S. was supported from the Marshall University Department of Chemistry alumni donors to the Marshall University Department of Chemistry’s Summer Undergraduate Research Fellowship.D.R.J.K. and A.L.S. were supported by the National Science Foundation under Cooperative Agreement No. OIA‐1458952. A.L.S. was also funded by the NASA West Virginia Space Grant Consortium, Grant #NNX15AK74A and Training Grant