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Sensitivity of cyanobacteria to a potential biological control agent, bacterium SG‐3

Cyanobacteria cause many problems in freshwater ecosystems. For example, the production of off‐flavor compounds by cyanobacteria causes serious problems in catfish aquaculture. Control of cyanobacteria is generally limited to treatment with copper compounds, which are non‐selective and sometimes ineffective at controlling certain species of cyanobacteria. Biological control could provide selective management by removing unwanted species while leaving desirable algae species. A bacterium (SG‐3) (NRRL B‐30043) lyses a number of planktonic species of cyanobacteria including bloom‐forming species of Anabaena and Oscillatoria . We tested SG‐3 for activity against 10 isolates, representing seven species, of mat‐forming cyanobacteria within the genera Oscillatoria, Lyngbya , and Phormidium . Plugs (0.5 cm diameter) were cut from mats of the cyanobacterium, inoculated with liquid cultures of SG‐3, and incubated as static cultures. The reduction in dry weights ranged from –0.5% to 90% compared to the untreated controls and appeared to be species specific. For example, dry weight reductions of Oscillatoria deflexoides and O. amoena ranged from 80 to 90% whereas the reduction of O. limosa tended to be lower at 36 to 72%. Although results varied among and within species, they indicate that this bacterium could have potential for use as a biological control for mat‐forming cyanobacteria. Light microscopic observations indicate the bacteria do not penetrate the cyanobacteria cells. Currently, we are studying the possible causes of the observed cell lysis.