The Effect of Chromium on Photosynthesis and Lipid Accumulation in Two Chlorophyte Microalgae

Heavy metals have adverse effects on microalgae growth and metabolism. Photosynthesis and lipid profile are quite sensitive to heavy metal toxicity. The impact of chromium (Cr) on growth and photosynthetic activity of Dictyosphaerium pulchellum and Micractinium pusillum exposed to different concentrations (0 – 500 μg L-1) was investigated for 11 days. The influence of Cr on cell density and cell number followed similar trends, indicating a possible correlation among these growth responses. A significant (p < 0.05) increase in lipid content was observed with the increasing concentration of Cr however, growth was suppressed at higher concentrations exceeding 100 μg L-1. Addition of Cr in the cell culture medium showed a negative effect on quantum yield (Fv/Fm) and a photosynthetic inhibition of > 65% was noted in both species at 500 μg L-1. However, the lipid gravimetric analysis presented inner cell lipid content up to 36% and 30% of dry weight biomass for D. pulchellum and M. pusillum, respectively. The effects of chromium on growth and lipid accumulation in both microalgae species was concentration and exposure time dependent. This shows that an appropriate concentration of chromium in culture medium could be beneficial for higher lipid accumulation in freshwater eukaryotic microalgae species.