Project description:Transcriptome analysis of Dunaliella viridis in response to changes in light duration and temperature Time course experiment experiment with 5 evenly spaced time points, t1-t5, and two experimental factors: a) light condition (2 levels: continuous light and light/dark cycle) and b) temperature (2 levels: 25 degrees Celsius and 35 degrees Celsius). Cells grown in the light/dark condition were exposed to a 12 hour light/dark cycle, whereas continuous light samples were grown under constant light conditions. All cells were grown at 25 degrees Celsius for timepoints t1 and t2; at time t3, cells grown in the high temperature condition were raised to 35°C, and kept at this temperature for the remainder of the experiment. Bar-coded samples were sequenced in two separate sequencing runs using 100-nt Illumina RNA-Seq reads. In the first run a single pooled biological replicate was sequenced from each of the 12 combinations of time, light condition and temperature from time points t3 to t5. The bar-coded samples were divided among 4 Illumina Lanes resulting in 48 distinct sequencing data files. In the second run ("Run 2") a single bar-coded biological replicate was sequenced from each of the 10 combinations of time and light condition from time points t1 through t5, with temperature fixed at 25°C.
Project description:Algal biofuel production requires an input of synthetic nitrogen fertilizer. Fertilizer synthesized via the Haber-Bosch process produces CO2 as a waste by-product and represents a substantial financial and energy investment. Reliance on synthetic fertilizer attenuates the environmental significance and economic viability of algae production systems. To lower fertilizer input, the waste streams of algal production systems can be recycled to provide alternative sources of nitrogen such as amino acids to the algae. The halophytic green alga Dunaliella viridis can use ammonium (NH4+) derived from the abiotic degradation of amino acids, and previously, supplementation of NH4+ from glutamine (GLN) degradation was shown to support acceptable levels of growth and increased neutral lipid production compared to nitrate. To understand the effect of glutamine-released NH4+ on algae growth and physiology, metabolite levels, growth parameters, and transcript profiles of D. viridis cultures were observed in a time course after transition from media containing nitrate as a sole N source to medium containing GLN, glutamate (GLU), or a N-depleted medium. Growth parameters were similar between GLN (NH4+) and nitrate supplemented cultures, however, metabolite data showed that the GLN supplemented cultures (NH4+) more closely resembled cultures under nitrogen starvation (N-depleted and GLU supplementation). Neutral lipid accumulation was the same in nitrate and glutamine-derived NH4+ cultures. However, glutamine-derived NH4+ caused a transcriptional response in the immediate hours after inoculation of the culture. The strong initial response of cultures to NH4+ changed over the course of days to closely resemble that of nitrogen starvation. These observations suggest that release of NH4+ from glutamine was sufficient to maintain growth, but not high enough to trigger a cell transition to a nitrogen replete state. Comparative transcript profiling of the nitrogen-starved and nitrate-supplied cultures show an overall downregulation of fatty acid synthesis and a shift to starch synthesis and accumulation. The results indicate that a continuous, amino acid derived slow release of NH4+ to algae cultures could reduce the amount of synthetic nitrogen needed for growth, but optimization is needed to balance nitrogen starvation and cell division.