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 (nTiO). 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 nTiO on Microcystis flos-aquae and Pseudokirchneriella subcapitata during inter-specific interaction was investigated. The specific growth rate (d) of M. flos-aquae exposed to nTiO 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 nTiO. The chlorophyll-a and total chlorophyll content of the monocultures of M. flos-aquae exposed to nTiO increased while other co-culture treatments significantly decreased these parameters. The experimental treatments, UVB, nTiO, and UVB + nTiO had differential effects on the pigment content of P. subcapitata. The total protein content, intracellular HO, 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 nTiO 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 nTiO in aquatic ecosystems.