Interactions microalgues-bactéries en système expérimental bispécifique : effets sur la croissance de Dunaliella sp.

The use of algae-bacteria mixed culture has been suggested to improve performance of industrial microalgae culture. The present study aims to investigate impact of selected bacteria on Dunaliella sp. growth. 97 bacteria strains were isolated from a variety of marine microalgae cultures. The diversity of strains revealed members of α-and γ-proteobacteria, Cytophaga-Flavobacterium-Bacteroides and grampositive. A two-phase approach was then implemented to select bacteria that improve Dunaliella sp. growth, using an original high-throughput experimental device. Although a majority of bacteria induced performance reduction for Dunaliella sp., some resulted in significant improvements. In nitrogenlimited batch culture, the Alteromonas sp. bacteria demonstrated a promoting effect on algal biomass accumulation and nitrogen yield. We assumed that higher culture yields were related to remineralization by Alteromonas sp of organic nitrogen released by Dunaliella sp. Conversely, in continuous culture, results suggested competition of bacteria for the limiting nitrogen. The apparent conflicting resutls between experiments may be related to balance between microalgae and bacteria populations and remaining nutrients. These results point out the potential of mixed cultures to improve Dunaliella sp. production. They also highlight complexity of underlying phenomena and the need for further work before considering application to industrial Dunaliella sp. production.