Interactions entre les bacteries et les algues dans une culture continue de phytoplancton naturel soumise aux conditions exterieures

During an experimental continuous culture of natural marine phytoplankton in environmental conditions, microbial and biochemical tests performed to study production of antibacterial and antialgal substances by unicellular algae. Some parameters were further monitored to characterize bacteria and phytoplankton growth. The presence of inhibitors of algal origin was studied both in the water and in the algal biomass at different phases of the culture, through bioassays performed with bacteria (marine pseudomonads and vibrios, and telluric strains) and several algal strains. Interpretation of the results is difficult. Two successive phases appeared during the growth of phytoplankton, with two different algal populations. The unsteady population of phase I was replaced during phase II by a stable one with a higher number of species; this might be due to the auto-inhibition of algae. Heterotrophic bacteria showed similar fluctuations which could be the consequence of algal ectocrines. The regulation of both bacterial and algal populations could be considered through ectocrine production of algal origin.