BACTERIAL PROTECTION OF MICROALGAE FACING CHEMICAL STRESS 

BARRIER (ANR PRCE ANR-22-CE34-0021) is a proof of concept project with multidisciplinary expertise for demonstrating, from the laboratory to a pilot process, that selected bacteria can protect microalgae when growing in various waters including produced water, seawater or wastewaters containing toxic compounds, providing higher algal resilience, productivity and bioremediation efficiency in saline wastewater treatments. Saline wastewater is a stubborn pollution source representing one of the most serious environmental problems occurring on land formations and in water reservoirs. In BARRIER project, natural microalgae and associated bacteria will be selected on organic and metallic toxic compounds. Microalgae-bacteria assemblages will be built, optimized through modeling and tested in large-scale mass culture processes using industrial wastewaters. Microalgae are promising organisms for producing a wide range of commodities (biofuel, bioplastics, …) including recycling and valuation of liquid and gaseous effluents. However, this is hindered by the difficulty to grow microalgae in contaminated waters, where various toxic may reduce their growth, and can even contribute to dramatic crash of the culture. Recent advances have shown that, when associated with a specific cluster of bacterial species, the resilience of assemblage can be significantly stronger than the microalgae alone.

Microalgae-bacteria consortia are shaped by complex interactions. Microalgae stimulate bacterial growth by the release of carbon exudates, whereas bacteria supply algae with vitamins and nutrients. Although the microalgae-bacteria relationships through metabolite exchanges are well studied, little is known however regarding the impact of chemical contaminants on the interactions between both microalgae and bacteria. Further experimental studies are required to understand the algae-bacteria interactions in the context of chemical pollution pressure in order to propose innovative strategies for improving the resilience of microalgae assemblage in contaminated effluents.

Four objectives in BARRIER project:

• To evidence the role of bacteria in the protection of microalgae against contamination, by analyzing physiological responses of microalgae under controlled exposure to toxic chemicals.

• To characterize the fate of toxic chemicals and organic matrix during the biodegradation/immobilization processes.

• To model and predict the role of interactions between microalgae and associated bacteria when exposed to combined toxic chemicals.

• To demonstrate in realistic outdoor pilot conditions that a selected microalgae-bacteria association provides a better resilience of the mass culture process and thus increases the yearly microalgal productivity and bioremediation processing in saline wastewaters with toxic contaminants.

BARRIER will perform complementary laboratory experiments in controlled and outdoor conditions with an upscaling approach using cultures of microalgae species and bacteria isolated from a contaminated environment.