The need for an economically-feasible, carbon-neutral fuel source rises as rates of carbon emissions increase and climate change persists. Diatom biodiesel is currently being researched as a carbon-neutral alternative to petroleum. Biochemical engineering, a method utilized to increase lipid accumulation in microalgae for harvest, works by stressing algal cultures in order to bias their metabolism towards lipid (fat) production. Although Nitrogen (N) is the most common limiting-nutrient in research, Silicon (Si) is also vital to diatom cell growth and division, and therefore its limitation would also cause an accumulation of lipids in cells. In fact, Si-limitation has yielded higher lipid content in diatoms than N-limitation without any of the severe physiological damage, making it a prime candidate for biochemical engineering of microalgae biodiesel. Two different species of diatom, Thalassiosira rotula and Coscinodiscus radiatus, were cultured and grown in a silicon- deficient media (20μM-Si) and in a silicon-rich media (80 μM-Si) to observe how differences in environmental Si affected frustule1 size, diatom growth rates, and lipid accumulation. We also stained the cells with dyes to observe Si frustules and lipid content, then took photographs with a fluorescent microscope for qualitative analysis. Our results suggested that diatom species had a greater impact on growth rate than Si treatment. Since all diatom species have different rates of growth, Si uptake and metabolism, it could be more prudent to focus on which species of diatom, rather than which nutrient-limitations, are best suited for biodiesel production
