Dynamics of Cyanophage-like Particles and Algicidal Bacteria Causing Microcystis aeruginosa Mortality

Abstract

The dynamics of cyanophage-like particles and algicidal bacteria that infect the bloom-forming cyanobacterium Microcystis aeruginosa was followed in a hypereutrophic pond from September 1998 to August 1999. The densities of M. aeruginosa ranged between 4.0 105 and 1.9 107 cells ml 1, whereas those of algicidal bacteria were between 4.0 and 5.1 102 plaque-forming units (PFU) ml 1 and those of cyanophage-like particles were between 5.0 102 and 7.1 103 PFU ml 1. A significant relationship was found between the densities of algicidal bacteria and M. aeruginosa (r 0.81, n 69, P 0.001), suggesting that the dynamics of the algicidal bacteria may regulate the abundance of M. aeruginosa. Occasional peaks of density of cyanophage-like particles were detected in October, June, and August, when sharp declines in M. aeruginosa cell densities were also observed. The densities of cyanophage-like particles became undetectable when the abundance of M. aeruginosa was low, suggesting the density-dependent infection of M. aeruginosa by cyanophage-like particles. Thus, we suggest that infections of both algicidal bacteria and cyanophage-like particles are important biological agents that decompose blooms of M. aeruginosa in freshwater environments.