Role of Predatory Bacteria in the Termination of a Cyanobacterial Bloom

Changes in cyanobacterial abundance and in the occurrence of bacteria capable of lysing cyanobacteria were monitored over a period of 6 months (May to October 1998) in eutrophic Brome Lake (Quebec, Canada), in which dense cyanobacterial blooms recur regularly. By screening lake water, we isolated two strains of lytic bacteria from the family Cytophagaceae. When tested on 12 cyanobacteria and 6 heterotrophic bacteria, strain 1 lysed only Anabaena flos-aquae and strain 2 lysed only Synechococcus cedorum, Synechococcus leopoliensis, Synechococcus elongatus, and Anacystis nidulans: both liquid and agar-grown cultures of these cyanobacteria were lysed. The number of plaque-forming units of bacteria increased dramatically during the decline of the bloom. The results are consistent with an important role for these host-specific lytic bacteria in control and elimination of cyanobacterial blooms in this lake.