Effect of ultraviolet radiation (type B) and titanium dioxide nanoparticles on the interspecific interaction between Microcystis flos-aquae and Pseudokirchneriella subcapitata.

Anthropogenic activities have led to the depletion of the ultraviolet radiation screening ozone layer, exposing aquatic biota to its harmful effects. Also, the rising applications of nanotechnology are resulting in the release and contamination of aquatic ecosystems with engineered nanometals like titanium dioxide nanoparticles (nTiO2). The rise in ultraviolet radiation interacts with nanometals, increasing their bioactivities to susceptible aquatic organisms such as algae and cyanobacteria. The effect of ultraviolet radiation B (UVB) and nTiO2 on Microcystis flos-aquae and Pseudokirchneriella subcapitata during inter-specific interaction was investigated. The specific growth rate (d-1) of M. flos-aquae exposed to nTiO2 increased significantly under monoculture conditions but was suppressed during co-culture with P. subcapitata. Contrarily, UVB stimulated the growth of the cyanobacterium regardless of the presence or absence of the green microalgae. However, there was a general decline in the growth of P. subcapitata following cultivation with M. flos-aquae and exposure to UVB and nTiO2. The chlorophyll-a and total chlorophyll content of the monocultures of M. flos-aquae exposed to nTiO2 increased while other co-culture treatments significantly decreased these parameters. The experimental treatments, UVB, nTiO2, and UVB + nTiO2 had differential effects on the pigment content of P. subcapitata. The total protein content, intracellular H2O2, peroxidase (POD), and glutathione S-transferase (GST) activity of both M. flos-aquae and P. subcapitata increased at varying degrees as a function of the treatment condition. Microcystin content was highest in co-cultures exposed to UVB. The results of this study suggest that increasing levels of nTiO2 and UVB significantly alter the growth and cellular metabolic activity of M. flos-aquae and P. subcapitata, but the cyanobacterium will probably be favored by increasing UVB levels and its interaction with nanometals like nTiO2 in aquatic ecosystems.

Effects of the antimalarial lumefantrine on Lemna minor, Raphidocelis subcapitata and Chlorella vulgaris.

Lumefantrine is used to treat uncomplicated malaria caused by pure or mixed Plasmodium falciparum infections and as a prophylactic against recrudescence following artemether therapy. However, the pharmaceutical is released into the aquatic environment from industrial effluents, hospital discharges, and human excretion. This study assessed the effects of lumefantrine on the growth and physiological responses of the microalgae Chlorella vulgaris and Raphidocelis subcapitata (formerly known as Selenastrum capricornutum and Pseudokirchneriella subcapitata) and the aquatic macrophyte Lemna minor. The microalgae and macrophyte were exposed to 200-10000 µg l-1 and 16-10000 µg l-1 lumefantrine, respectively. Lumefantrine had a variable effect on the growth of the aquatic plants investigated. There was a decline in the growth of R. subcapitata and L. minor post-exposure to the drug. Contrarily, there was stimulation in the growth of Chlorella vulgaris. All experimental plants had a significant increase in lipid peroxidation, which was accompanied by an increase in malondialdehyde content. Peroxidase activity of L. minor increased only at low lumefantrine concentrations, while the opposite occurred at higher levels of the drug. Incubation in lumefantrine contaminated medium significantly up-regulated the activity of R. subcapitata cultures. Glutathione S-transferase of L. minor exposed to lumefantrine treatments had substantially higher activities than the controls. Our findings suggest lumefantrine could have adverse but variable effects on the growth and physiology of the studied aquatic plants.