Relationships between bacteria and cyanobacteria in the Marrakech waste stabilisation ponds

In waste stabilisation pond systems the interactions between algae and bact eria have an important ecological effect and appeared to play a key role in the self-purification process. The aim of the present study is to evaluate the interactions between two axenic cyanobacteria: Synechocystis sp, and P seudanabaena sp. with heterotrophic bacteria and some pathogenic bacteria: E. coli, Salmonella sp, and non-O1 V. cholerae. The results obtained showed that Synechocystis sp. (planktonic cyanobacterium) and Pseudanabaena sp. ( benthic cyanobacterium) stimulated the growth and the survival of heterotro phic bacteria and non-Ol V. cholerae and reduced the survival of E. coil an d Salmonella. Blooms of these cyanobacteria during hot periods which are a particularity in stabilisation ponds of Marrakech, could explain the dynami cs of bacteria studied in this sewage treatment process. The presence of he terotrophic bacteria, showing relative high densities during hot periods, c ould be considered as an important biotic factor which led to the cyanobact eria blooms in the Marrakech ponds which function under an arid Mediterrane an climate.