Influence of Silver, Zinc Oxide and Copper Oxide Nanoparticles on the Cyanobacterium Calothrix elenkinii

Abstract

An investigation was undertaken to compare the effect of different concentrations of three metal nanoparticles i.e. silver (Ag), zinc oxide (ZnO) and copper oxide (CuO), on a cyanobacterium Calothrix elenkinii. Chlorophyll accumulation in C. elenkinii acclimatised to Ag NPs after 1 week at concentrations of 0.1 and 0.5 mg L−1, while it reduced at 1.0 mg L−1. A similar trend was recorded with CuO NPs, in terms of protein content with incubation time. Nitrogen-fixing potential also showed a gradual increase with Ag NPs, up to concentrations of 0.2 mg L−1 during incubation of 1 week, but sharply decreased at 0.5 mg L−1 after 48 h. Both the nitrogen-fixing potential and protein content were stimulated in the presence of CuO NPs. ZnO NPs, in general, were not compatible with the growth and metabolic activities of this cyanobacterium. Microscopic studies revealed the aggregation of NPs on the surface of C. elenkinii filaments, resulting in distinct morphological changes, particularly enhanced hormogonia and akinete formation. It is envisaged that with the increase in incubation period, C. elenkinii acclimatised to counteract the effect of Ag and CuO NPs and utilise them for its growth. The adaptive strategies of this cyanobacterium make it an ideal model system for future nanotoxicological studies.