EXPERIMENTAL-STUDY OF THE EFFECT OF SYNECHOCYSTIS SP. (PICOCYANOBACTERIA) ON THE BEHAVIOR OF SOME BACTERIA OF SANITARY INTEREST

In aquatic ecosystems, bacterial behaviour is controlled by several bi otic factors, especially by microalgae. The aim of this study is to de termine the effect of a picocyanobacteria Chroococcale : Synechocystis sp. on the behaviour of some bacteria (Escherichia coli, Salmonella s p. 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 controlle d conditions of light and temperature. Extracellular and intracellular products released by this microalga were tested on the bacteria. Extr acellular products obtained at the supernatant of algal culture in sta tionary phase, reduced E. coli and Salmonella sp, growth and stimulate d 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 fo r the axenic and the non axenic algal strain. The results showed that the presence of heterotrophic bacteria increased the reduction of E. c oli and Salmonella sp. growth by extracellular and intracellular produ cts of Synechocystis sp.. Blooms of this picocyanobacteria in waste st abilization ponds of Marrakesch, could explain the dynamics and surviv al of bacteria studied in this ecosystem which functions under an arid mediterranean climate.