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.
