The relationship between Chlorella sp. and zinc oxide nanoparticles: Changes in biochemical, oxygen evolution, and lipid production ability

In this study, the effect of different concentrations (50, 100, and 200 mg L-1) of zinc oxide nanoparticles (ZnO-NP) on the biochemical changes, oxygen evolution, and lipid production in Chlorella sp. were analyzed. The growth rate, oxygen evolution capacity, total carotenoids and protein, starch, and neutral lipid were determined using UV spectrophotometer, oxytherm electrode system, microplate, and fluorescence spectrometer, respectively. Triacylglycerol, polysaccharides, and oligosaccharides were quantified using FT-IR. The results of FT-IR, TGA, and XRD analysis revealed the existence of stretching mode of Zn-O bond (496 cm(-1)), thermal stability, and crystalline domain size (18.7 nm) of ZnO-NP. Among the three concentrations, increased specific growth rate (0.72-fold) and oxygen evolution capacity (0.96-0.90 nmol/min) without aggregation was obtained in 50 mg L-1 of ZnO-NP treated cells. Conversely, no complete inhibition was observed in the growth and oxygen evolution at higher concentrations. The optimal concentration (50 mg L-1) of ZnO-NP demonstrated that the highest level of total carotenoids (1.23-fold), total protein (1.68-fold), starch (2.26-fold), neutral lipid (6.08-fold), and triacylglycerol (8.21-fold) were recorded on day 2. We conclude that 50 mg L-1 of ZnO-NP treatment enhanced the production of neutral lipids and triacylglycerol without complete inhibition of growth.