Impairment of benthic diatom adhesion and photosynthetic activity by 2E,4E-decadienal.

Within biofilms, microorganisms are exposed to a wide range of chemicals released by phototrophic organisms. Those chemicals are likely to influence the dynamics and functioning of biofilms. 2E,4E-decadienal (DD) is a polyunsaturated aldehyde produced by diatoms which is known to induce adverse effects in many aquatic organisms. It has been shown to inhibit the adhesion and motility of one benthic diatom. The aim of this article was to determine if the effects of DD on diatom adhesion were widespread and if it could affect biofilm formation and functioning. The adhesion of 5 of 10 benthic diatom strains was strongly inhibited at 2.5 μg ml(-1) DD. This indicates a high variability in diatom sensitivity to DD. Several experiments in microcosms showed that the presence of DD diffusing from a substrate decreased biofilm formation. This effect was dose-dependent and persisted for 72 h, though the molecule is highly volatile. Using a PHYTO-PAM fluorometer, we also showed that the effective quantum efficiency of charge separation of PSII of biofilms exposed to DD was negatively affected. This indicates a decrease in the efficiency of the photochemical processes. All these results suggest that the presence of DD-producing strains may have a significant impact on the composition and physiology of biofilms.