Gene expression and lipid accumulation in green microalga chlamydomonas reinhardtii (137c) under salt stress condition

Abstract

Biodiesel is an important alternative energy that can reduce CO2 emission, the main cause of Global warming. Algal biomass has been considered to be the third generation biofuels. One of the important strategies that enhance lipid accumulation; precursor of biodiesel production, is stress cultivation. High salt concentration is one of a potential approach to enhance lipid accumulation in microalgae. Here, we investigated the impacts of salt on lipid accumulation in green microalga Chlamydomonas reinhardtii (137c). The results revealed that higher concentrations of NaCl, KCl, and LiCl led to increasing of saturated fatty acid contents for 1.8, 1.2, and 1.1 folds compared with control condition. Poly-unsaturated fatty acid contents were found to be statistically significant decreased. The expression level of seven genes involved in lipid biosynthesis was examined under NaCl stress. PDH2, MAT, and KAS2 were up-regulated significantly for 1.83 ± 0.20, 1.82 ± 0.06, and 1.70 ± 0.05 folds, respectively. In this study, we were interested in the expression ChMAT and overexpression of SynMAT in the model freshwater cyanobacterium Synechococcus elongatus PCC 7942. Expression of ChMAT could be detected at transcriptional level but not translational level. In case of SynMAT overexpressor, gene and protein expression obviously detected. Under different growth phase of SynMAT/7942, gene and protein expressions were not different. SynMAT and SynLACS mRNA expression under salt stress; however, seemed to be down-regulated. Fatty acid composition was modulated in the overexpressor. FAMEs analysis demonstrated that overexpression of SynMAT in S. elongatus PCC 7942 resulted in increasing of total saturated fatty acid while mono-unsaturated fatty acid content was decreased. Moreover, overexpression of SynMAT affected to the content of C16 and C18 in particular. This study would lead to the improvement of lipid accumulation in microalgae or cyanobacteria in the future.