Interaction of copper oxide nanoparticles with the cyanobacterium Synechococcus sp.: toxic effects and oxidative stress development
摘要
Cyanobacteria of the genus Synechococcus represent a globally distributed and ecologically important group of prokaryotic microalgae. The existing knowledge on the effect of copper oxide nanoparticles (CuO NPs) on the physiology and functioning of this group of microorganisms is fragmentary. In the presented study, a comprehensive evaluation of the toxic effects of CuO NPs on physiological parameters of the phycoerythrin-containing cyanobacterium Synechococcus sp., BS 9001 was carried out. It was shown that a significant decrease in the specific growth rate of Synechococcus sp. was observed at the content of pollutant in the medium above 0.5 mg L−1. Increasing of CuO NPs concentration leads to an increase in the proportion of cells with low pigment content and low functional (matabolic) activity. However, even under extremely unfavorable growth conditions, a cluster of cells resistant to the effect of CuO NPs is registered in the population. The toxic effect of CuO NPs on photosynthetic activity of Synechococcus sp. is manifested in a decrease in the quantum efficiency of photosynthesis and the relative rate of electron transport. Analysis of morphophysiological changes in Synechococcus sp. cells showed a pronounced elongation of cells, indicating the development of morphological defects upon exposure to CuO NPs due to disruption of the division process. The study did not reveal aggregation of Synechococcus sp. cells with CuO NPs. The effect of mechanical exposure to CuO NPs was expressed only in the damage of cell membrane integrity. Increasing the concentration of CuO NPs in the medium led to a change in the pigment composition of Synechococcus sp., a decrease in the ratio of phycoerythrin to chlorophyll and an increase in the ratio of phycourobilin to phycoerythrobilin in the cells were observed, which is associated with dissociation of the latter in antenna complexes. Exposure to low-frequency CuO NPs led to a progressive increase in the production of reactive oxygen species (ROS) and a decrease in the metabolic activity of Synechococcus sp. cells, indicating the development of oxidative stress. The increase of ROS in cells correlated with the deterioration of all studied physiological and biochemical parameters of Synechococcus sp., indicating the inability of the defense mechanisms of the studied cyanobacterium to cope with the induced oxidative damage. The obtained results contribute to understanding the mechanisms of toxic effect of metal oxide nanoparticles on cyanobacteria and assessing the ecological consequences of their ingestion into the environment.