Impact of nitrogen limitation on biomass, photosynthesis, and lipid accumulation in Chlorella sorokiniana
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Induction of oil accumulation in algae for biofuel production is often achieved by withholding nitrogen. However, withholding nitrogen often reduces total biomass yield. In this report, it is demonstrated that Chlorella sorokiniana will not only accumulate substantial quantities of neutral lipids when grown in the absence of nitrogen but will also exhibit unimpeded growth rates for up to 2 weeks. To determine the physiological basis for the observed increase in oil and biomass accumulation, we compared photosynthetic and respiration rates and chlorophyll, lipid, and total energy content under ammonia replete and deplete conditions. Under N-depleted growth conditions, there was a 64 % increase in total energy density and a ∼20-fold increase in oil accumulation relative to N-replete growth leading to a 1.6-fold greater total energy yield in N-depleted than in N-replete cultures. We propose that the higher energy accumulation in N-depleted cultures is due to enhanced photosynthetic energy capture and conversion associated with reduced chlorophyll levels and reduced self-shading as well as a shift in metabolism leading to the accumulation of oils.
KeywordsMicroalgae Chlorella sorokiniana Photobioreactor Lipid production Biofuels Photosynthesis
We thank Paige Pardington for her help in assisting with the photobioreactors during this experiment. This work is supported by the U.S. Department of Energy under contract DE-EE0003046 awarded to the National Alliance for Advanced Biofuels and Bioproducts for RTS and TS and by the Center for Animal Health and Food Safety at New Mexico State University for TS.
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