Background: Marine ecosystems contain benthic microalgae and bacterial species that are capable of secreting extracellular polymeric substances (EPS), suggesting that settlement of these microorganisms can occur onsubmerged surfaces, a key part of the first stage of biofouling. Currently, anti-fouling treatments that helpcontrol this phenomenon involve the use of biocides or antifouling paints that contain heavy metals, whichover a long period of exposure can spread to the environment. The bacterium Alteromonas sp. Ni1-LEM has an inhibitory effect on the adhesion of Nitzschia ovalis, an abundant diatom found on submerged surfaces.

Results: We evaluated the effect of the bioactive compound secreted by this bacterium on the EPS of biofilms andassociated epiphytic bacteria. Three methods of EPS extraction were evaluated to determine the mostappropriate and efficient methodology based on the presence of soluble EPS and the total protein and carbohydrate concentrations. Microalgae were cultured with the bacterial compound to evaluate its effect on EPS secretion and variations in its protein and carbohydrate concentrations. An effect of the bacterial supernatant on EPS was observed by assessing biofilm formation and changes in the concentration of proteins and carbohydrates present in the biofilm.

Conclusions: These results indicate that a possible mechanism for regulating biofouling could be through alteration of biofilm EPS and alteration of the epiphytic bacterial community associated with the microalga.