The world crude oil supply is decreasing at an alarming rate and no longer represents a long-term solution to meet energy needs. Development of renewable energy is required to meet transport fuel demands. Algal biofuels represent a potentially viable option. Diatom strain, RGd-1, isolated from Yellowstone National Park, produces high concentrations of lipids that can be used for biodiesel production. To increase cell numbers, RGd-1 was grown in six silica concentrations; without added silica, four silica concentrations within the soluble range (0.5-2mM), and one just above the soluble range (2.5 mM). Increasing the silica concentration resulted in an increase in total cell numbers and dry cell weight. Silica depletion was verified by ICP-MS. When grown in higher silica concentrations the medium reached higher pH, which remained elevated for the remainder of each experiment. Once silica was depleted, the rate of Nile Red fluorescence increased. Unlike green algae and other diatoms, nitrate was never depleted when using the standard Bolds Basal Medium concentration (2.94 mM). However, based on previous studies, approximately 1/3 of the original nitrate concentration (1 mM) was utilized once cells reached stationary phase. Therefore, 1mM of nitrate was added to potentially induce a dual nitrate and silica stress. Sodium bicarbonate was added to cells grown with each of the aforementioned nitrate concentrations. Coupling nitrate limitation with sodium bicarbonate addition resulted in higher Nile Red fluorescence compared to other conditions. RGd-1 fatty acids exist primarily as C16:0, C16:1, C18:1-3 and C20:5, averaging at approximately 35, 30, 16 and 10%, respectively of the total lipid content. With exception of cells grown without added silica, the lipid content per biomass was approximately the same (20-30% (w/w) TAG (Triacylglycerol) and 50-60% (w/w) fatty acid methyl ester (FAME) grown under all conditions within the soluble range. However, when factoring in the dry cell weight from each system, it was found the TAG and FAME concentration increased with silica concentration.
Diatom biofuels: Optimal nutrient requirements for lipid production, Thesis Defense by Karen M. Moll, M.S. Candidate, department of microbiology, Montana State University, August 2012