Abstract
Microalgae are used as a source of lipids for the production of biofuels. Most algae produce neutral lipids under stress conditions. Here, lipid accumulation by the unicellular alga Chlamydomonas reinhardtii was examined during cultivation under iron-limiting conditions. Severe iron stress caused the cells to accumulate a significant amount of lipid, specifically triacylglycerols (TAGs), by compromising the growth. Semi-quantitative measurements by Fourier transform infrared (FTIR) spectroscopy showed an increase in both carbohydrate and lipid content in iron-stressed C. reinhardtii cells compared to control. Analysis by flow cytometry and thin layer chromatography confirmed that severe iron deficiency-induced TAG accumulation to fourfold higher than in iron-replete control cells. This accumulation of TAGs was mostly degraded from chloroplast lipids accompanied by overexpression of diacylglycerol acyltransferase (DGAT2A) protein. Furthermore, liquid chromatography-mass spectrometry (LC-MS) analysis demonstrated significantly enhanced levels of C16:0, C18:2, and C18:3 fatty acids (FAs). These results indicate that iron stress triggers the rapid accumulation of TAGs in C. reinhardtii cells. The enhanced production of these lipids caused by the iron deficiency may contribute to the efficient production of algal biofuels if we escalate to the photobioreactor’s growth conditions.
Highlights
Photosynthetic algae capture solar energy and store it as chemical energy in the form of starch and lipids, triacylglycerols (TAGs) (Merchant et al, 2007)
We recently reported the effect of iron stress conditions on cellular biomass and the proteins involved in lipid biosynthesis in C. reinhardtii (Devadasu et al, 2019)
Traces of iron were utilized by the cells for initial multiplication in the iron-deficient medium, so genuine iron stress only occurred after the first cell division
Summary
Photosynthetic algae capture solar energy and store it as chemical energy in the form of starch and lipids, triacylglycerols (TAGs) (Merchant et al, 2007). Nitrogen starvation severely inhibits algal growth and induces TAG accumulation in C. reinhardtii cells (James et al, 2011). We hypothesized that two-stage iron starvation, i.e., cells initially subjected to iron deficiency are further cultured in an iron-depleted medium to cause severe iron starvation, might effectively induce lipid accumulation in C. reinhardtii. This so-far untested treatment regime could offer a simple way of increasing lipid content in microalgae. Its genome has been sequenced; it is easy to grow in culture and has a wellcharacterized response to adverse environmental conditions This organism was selected to investigate the influence of two-stage iron starvation on TAG accumulation. Severe iron starvation conditions significantly increased the production of TAGs, which will help to make biofuel production for more efficient
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