The Effect of Salinity Stress and Nitrogen Depletion on Neutral Lipid Production by the Green Microalgae Auxenochlorella and Chlorella

During the past decade, microalgae have been studied as potential sources for biofuel production. In this study, two species of green microalgae were isolated from Weston Park pond in Sheffield, UK and identified using 18S rDNA sequencing as Auxenochlorella and Chlorella. The neutral lipid (triacylglycerol, TAG) content of Auxenochlorella and Chlorella was measured using the fluorescent dye Nile Red. Neutral lipid, in the form of TAG, can easily be converted to biodiesel using transesterification. Therefore, the effects of stress conditions on neutral lipid accumulation by both microorganisms were tested to evaluate their potential for the production of biodesel. For salinity stress, the highest percentage TAG content (24%) was found in Auxenochlorella cells grown at 0.8 M NaCl for three weeks. For Chlorella, the highest TAG was 26% in cells grown at 1 M NaCl for 4 weeks. Neutral lipid accumulation also increased significantly with nitrogen starvation for 4 weeks reaching 44% in Auxenochlorella, while in Chlorella, it was 70%. Therefore, the percentage of neutral lipid accumulated was much higher under nitrogen stress than under salinity stress.