A new method for evaluation of antifouling activity of molecules against microalgal biofilms using confocal laser scanning microscopy-microfluidic flow-cells

Abstract Regulatory developments regarding antifouling molecules encourage the search for non-toxic substances. Evaluation tools must evolve to highlight anti-adhesion effects rather than growth inhibition. The work presented here aimed at developing a method based on confocal laser scanning microscopy-microfluidic flow-cells in order to characterize microalgal biofilms. The first part of the work was dedicated to the setting-up of experimental parameters allowing the production of microalgal biofilms. The results obtained showed that it was indeed possible to produce reproducibly biofilms. The size of microalgal strains appeared to be a key-parameter in the adhesion rate and cells adhesion strength. Cylindrotheca closterium cells adhered in lower amount but formed denser biofilms than Porphyridium purpureum . The second part of the work focused on the evaluation of a known antifouling molecule, dibromohemibastadin-1 (DBHB). A comparison with the conventionally used method, multi-well plates experiments, was established. The multi-well plates experiments allowed the determination of minimum inhibitory concentration (MIC) for growth and adhesion inhibition (around 80 μM). The flow-cells combined with confocal laser scanning microscopy (CLSM) enabled the observation of biofilm, the determination of kinetics parameters of adhesion and an estimation of the adhesion strength.