Effects of biological control agents on nuisance cyanobacterial and diatom blooms in freshwater systems

Abstract

Biological control agents such as bacteria and ciliates were tested alone and in combination for their abilities to decrease densities of the warm-weather cyanobacterium, Microcystis aeruginosa, and the cold-weather centric diatom, Stephanodiscus hantzschii. The growth of Microcystis aeruginosa was effectively suppressed by the algicidal bacterium, Streptomyces neyagawensis, and the predator heterotrich ciliate, Stentor roeselii. However, co-treatment increased the algal density rather than decreasing it, suggesting that Streptomyces neyagawensis and Stentor roeselii have an antagonistic relationship. Additional experiments revealed that the density of Stephanodiscus hantzschii was effectively reduced by the bacterium, Pseudomonas putida, and by the abovementioned strain of Stentor roeselii. Co-treatment had a greater antialgal effect than treatment with either bio-agent alone, indicating that the two act synergistically. These results suggest the potential antialgal efficacy of treatments with multiple biological control agents, providing new insight that may be useful for the bioremediation of nuisance algal blooms in freshwater.