Abstract

Eukaryotic marine microalgae like Dunaliella spp. have great potential as a feedstock for liquid transportation fuels because they grow fast and can accumulate high levels of triacylgycerides with little need for fresh water or land. Their growth rates vary between species and are dependent on environmental conditions. The cell cycle, starch and triacylglycerol accumulation are controlled by the diurnal light:dark cycle. Storage compounds like starch and triacylglycerol accumulate in the light when CO2 fixation rates exceed the need of assimilated carbon and energy for cell maintenance and division during the dark phase. To delineate environmental effects, we analyzed cell division rates, metabolism and transcriptional regulation in Dunaliella viridis in response to changes in light duration and growth temperatures. Its rate of cell division was increased under continuous light conditions, while a shift in temperature from 25°C to 35°C did not significantly affect the cell division rate, but increased the triacylglycerol content per cell several-fold under continuous light. The amount of saturated fatty acids in triacylglycerol fraction was more responsive to an increase in temperature than to a change in the light regime. Detailed fatty acid profiles showed that Dunaliella viridis incorporated lauric acid (C12:0) into triacylglycerol after 24 hours under continuous light. Transcriptome analysis identified potential regulators involved in the light and temperature-induced lipid accumulation in Dunaliella viridis.

Highlights

  • Marine microalgae have been investigated for their great potential as feedstocks for renewable liquid transportation fuels because they could replace petroleum-derived fuels without competing for resources like land or fresh water required for food and feed production [1,2]

  • Because regulation of oil accumulation and cell division are diurnally regulated in algae [21,22,23], we studied the responses of Dunaliella spp. to changes in photoperiod as well as temperature, and the combination of both environmental effects

  • For a detailed metabolic and genomic analysis of the regulation underlying this response, we selected Dunaliella viridis dumsii because it showed the highest oil increase under induction when grown under LL at elevated temperature in comparison to other strains

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Summary

Introduction

Marine microalgae have been investigated for their great potential as feedstocks for renewable liquid transportation fuels because they could replace petroleum-derived fuels without competing for resources like land or fresh water required for food and feed production [1,2]. Several Dunaliella spp. grow well under high levels of salt, which reduces culture contamination with other microorganisms or pathogens [5,6]. Dunaliella spp. lack a cell wall [4], which enables the extraction of oil droplets by osmotic shock in freshwater as one of the most inexpensive and environmental friendly ways to extract oil from algae cultures [10]. Despite all these useful traits of Dunaliella for bioenergy production, production of algae oil for liquid transportation fuels is commercially not viable. We focused our research on the regulation of cell division rates and oil content in Dunaliella by environmental control

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