Photosynthetic efficiency and compositional alterations in microalgae Chlorella vulgaris in response to changes in the pH condition

摘要

Present investigation on the effect of varying extracellular pH conditions (pH 6.5-10.5) on growth, accumulation of cell constituents and photosynthetic performance of microalga Chlorella vulgaris revealed that slightly alkaline pH (7.5-8.5) was the preferred pH range for growth, synthesis of protein and carbohydrate. Whereas total organic carbon (TOC) and lipid content in the microalga gradually increased with pH ranging ranging from 6.5 to 10.5. The FTIR results on total lipid (1740 cm- 1), lipid/carbohydrate (1740/1650 cm- 1) and lipid/protein (1740/1040 cm- 1) ratio in the cells grown at pH 6.5, 8.5 and 10.5 supported the above observation on the estimated amount of macromolecules. The chlorophyll fluorescence induction kinetics (OJIP), exhibiting various photosynthetic parameters, showed initial improvement in the photosynthetic efficiency between pH 6.5-8.5, followed by pH dependent declining pattern. Addition of HCO3- (20 mM) showed little effect on the photosynthetic electron transport. Theenergy dependent quenching parameters of chlorophyll fluorescence like ABS/RC, NPQ and qE, usually associated with the energy state of the membrane, registered an increasing trend with rising pH (pH 6.5-10.5). Use of energy inhibitors DNP, CCCP and electron acceptors/donors (methyl viologen and phena-zine methosulphate) on ABS/RC, NPQ and qE suggested that pH dependent regulation of photosynthetic performance in C. vulgaris was tightly coupled with proton gradient of the membrane and that was reversedby the energy uncouplers like DNP and CCCP or electron acceptor like MV.