Growth reduction of Microcystis aeruginosa by clay ball elution solution

Abstract

Abstract Clay is a natural material, and its transportation via rivers to estuaries is influenced by man-made structures. We hypothesized that chemicals eluted from clay affect bloom bacteria. To evaluate this hypothesis, we created an environment in which bacteria were separated from clay using clay balls. When Microcystis aeruginosa was incubated with clay balls, the growth rate at and after the late exponential phase decreased by two-thirds compared to that of Microcystis incubated without a clay ball. The clay ball adsorbed ammonia and phosphorus at neutral pH, but this was not the main reason for the growth reduction. Incubation in Microcystis aeruginosa (MA) medium made of a clay ball-soaked solution, a cement ball-soaked solution, a silicate solution, and distilled water revealed that the growth of Microcystis was significantly lower in the MA medium made of the clay ball-soaked solution, whereas there was no difference in growth among the other solutions. None of the solutions exerted a negative influence on the growth of Achnanthidium minutissimum. These results suggest that the growth reduction of Microcystis was due to a combined effect by silicate and other chemical compounds eluted from the clay ball. These findings may improve our understanding of cyanobacterial blooms and enhance water management.