Effects of glyphosate at environmentally relevant concentrations on the growth of and microcystin production by Microcystis aeruginosa

The use of glyphosate, which is a well-known sterilant herbicide, has been growing rapidly because the area under the cultivation of genetically modified crops that are tolerant to this herbicide has increased. Glyphosate can enter into aquatic systems through many different ways. However, information on the potential risks of glyphosate at environmentally relevant levels to aquatic systems is still limited. In this study, we selected the cyanobacterium Microcystis aeruginosa FACHB905 (M. aeruginosa) as a model organism to evaluate the effects of glyphosate at environmentally relevant concentrations on the former's growth and microcystin (MC) production. Our results show that low levels of glyphosate stimulate the growth of M. aeruginosa. Subsequently, there was significant increase in the total MC-LR and intracellular MC-LR, but not in extracellular MC-LR, after exposure to 0.1-2 mg/L of glyphosate. The increase in total MC-LR is mainly due to the effects of glyphosate on the cell density of M. aeruginosa. The data provided here show that low level of glyphosate in a water body is a potential environmental risk factor that stimulates the growth and enhances MC production in M. aeruginosa, which should arouse great concern.