Experimental study of the effect of Synechocystis sp. (picocyanobacteria) on the behaviour of some bacteria of sanitary interest

In aquatic ecosystems, bacterial behaviour is controlled by several biotic factors, especially by microalgae. The aim of this study is to determine the effect of a picocyanobacteria Chroococcale : Synechocystis sp. on the behaviour of some bacteria (Escherichia coli, Salmonella sp. and non-O1 Vibrio cholerae:). Blooms of this algae occur during hot periods in wastewater stabilization ponds of Marrakesch. The alga was isolated from the ponds and cultivated in the laboratory at controlled conditions of light and temperature. Extracellular and intracellular products released by this microalga were tested on the bacteria. Extracellular products obtained at the supernatant of algal culture in stationary phase, reduced E. coli and Salmonella sp, growth and stimulated growth of non-O1 V. cholerae. Intracellular products obtained after lysing algal cells by ether, reduced E. coli and Salmonella sp. growth. The effect of products released by Synechocystis sp. was compared for the axenic and the non axenic algal strain. The results showed that the presence of heterotrophic bacteria increased the reduction of E. coli and Salmonella sp. growth by extracellular and intracellular products of Synechocystis sp.. Blooms of this picocyanobacteria in waste stabilization ponds of Marrakesch, could explain the dynamics and survival of bacteria studied in this ecosystem which functions under an arid mediterranean climate.