Photosynthetic performance, nutrient status and lipid yield of microalgae Chlorella vulgaris and Chlorococcum humicola under UV-B exposure

Abstract

The present study was conducted to examine the photosynthetic performance, nutrient status and lipid yield in microalgae Chlorococcum humicola and Chlorella vulgaris under different durations of UV-B exposure (1/2 h, 1 h, 2 h, 3 h and 4 h). Results revealed that UV-B reduces the photosynthetic performance of photosystem II by altering photosynthetic performance index (Pi ABS ), maximum quantum yield (Fv/Fm), net closing rate of reaction centre (Mo), trapping flux (TRo/RC) and effective antenna size with their respective control. Scanning Electron Microscopy (SEM) exhibited variegated structure and increased cell size by ~15–65% which was more pronounced in the case of C. humicola at 4 h of UV-B. The Energy Dispersive Spectroscopy (EDS) data showed that the content of microelements (C, O, Na, and K) in terms of atomic weight % was found to be significantly increased in C. vulgaris while with C. humicola , it was restricted to carbon (C) only. Further, the high antioxidant (ascorbic acid, cysteine and proline) potential and carotenoid/chl a photoprotection response reflects protection against UV-B in the both algae. In the case of lipid, comparative greater increase in cell size of C. humicola correlated with high lipid yield as compare to C. vulgaris at 2 h of UV-B could be employed in the production of biofuel in sustainable manner. Thus, algae C. humicola could be a best alternative feed stock of lipid and biofuel production in the area receiving high solar radiation. • UV-B exposure of 4 h exhibited toxicity in algae C. humicola and C. vulgaris . • UV-B exposure significantly reduces photo system II performance of both algae. • Under 2 h UV-B exposure lipid yield in C. humicola was higher than C. vulgaris . • SEM-EDS revealed altered essential minerals and cell size in algae under UV-B.