Stress induced lipid production in Chlorella vulgaris: Relationship with specific intracellular reactive species levels

Abstract

Microalgae have significant potential to be an important alternative energy source, but the challenges to the commercialization of bio-oil from microalgae need to be overcome for the potential to be realized. The application of stress can be used to improve bio-oil yields from algae. Nevertheless, the understanding of stress effects is fragmented due to the lack of a suitable, direct quantitative marker for stress. The lack of understanding seems to have limited the development of stress based strategies to improve bio-oil yields, and hence the commercialization of microalgae-based bio-oil. In this study, we have proposed and used the specific intracellular reactive species levels (siROS) particularly hydroxyl and superoxide radical levels, separately, as direct, quantitative, markers for stress, irrespective of the type of stress induced. Although ROS reactions are extremely rapid, the siROS level can be assumed to be at pseudo-steady state compared to the time scales of metabolism, growth and production, and hence they can be effective stress markers at particular time points. Also, the specific intracellular (si-) hydroxyl and superoxide radical levels are easy to measure through fluorimetry. Interestingly, irrespective of the conditions employed in this study, that is, nutrient excess/limitation or different light wavelengths, the cell concentrations are correlated to the siROS levels in an inverse power law fashion. The composite plots of cell concentration (y) and siROS (x) yielded the correlations of y = k1 · x(-0.7) and y = k2 · x(-0.79) , for si-hydroxyl and si-superoxide radical levels, respectively. The specific intracellular (si-) neutral lipid levels, which determine the bio-oil productivity, are related in a direct power law fashion to the specific hydroxyl radical levels. The composite plot of si-neutral lipid levels (z) and si-hydroxyl radical level (x) yielded a correlation of z = k3 · x(0.65) . More interestingly, a nutrient shift caused a significant change in the sensitivity of neutral lipid accumulation to the si-hydroxyl radical levels.

Size of Paramecium bursaria individuals under cold and dark conditions

“…Chlorella species (including the photobiont, C. variabilis) generally produce starch to store photosynthates (Reisser 1987(Reisser , 1988Luo et al 2010). However, recent studies show that Chlorella algae also produce lipids or oils prolifically under certain conditions (Přibyl et al 2012;Chen et al 2013;Menon et al 2013). It is therefore likely that the achromic drops observed in the present study were lipids and that photobionts may produce large quantities of lipids under cold, dark conditions.…”

Synergistic effect of UV radiation and nutrient limitation on Chlorella fusca (Chlorophyta) cultures grown in outdoor cylindrical photobioreactors

“…However, it is noteworthy that lipid peroxidation did not happen in the full nutrient treatment, which can be attributed to the full effec-tiveness of repair mechanisms that had no limitation from nutrient availability. Nutrient limitation is known to induce ROS production and decrease the repair capability of a cell (Berges & Falkowski 1998, Logan et al 1999, Bucciarelli & Sunda 2003, Menon et al 2013). Here, the combined effect of limitation of essential nutrients like N and S needed for oxidative repair mechanisms under PAB conditions resulted in increased lipid peroxidation (Lesser et al 1994, Litchman et al 2002, Van De Poll et al 2005.…”

Phycoremediation-Coupled Biomethanation of Microalgal Biomass

“…This, in turn, depends on the cultivation conditions. For instance, microalgae accumulate lipids under nitrogen starvation conditions (Menon et al, 2013) and carbohydrates under phosphorous limitations (Markou et al, 2013). Hence, the biomass composition of the same alga may differ when grown in different types of wastewater, depending on the nutrient profile of the wastewater (Prajapati et al, 2014c).…”