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

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 similar to 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.