Anti-biofilm and anti-fouling agent from Agardhiella subulata (Rhodophyta)

Macroalgae biomass of the coastal brackish lake of Ganzirri (Messina, Italy) needs to be periodically removed and treated as waste. Bacterial biofilm formation is one of the most relevant concerns in a wide range of domains, from aquaculture to marine environmental aspects, including biofouling. Natural polysaccharides, including carragenans from red macroalgae, have been considered as alternative materials promising for marine anti-fouling coatings. In an ongoing screening for novel environment-friendly anti-biofouling molecules, in this study, crude polysaccharide (κ-carrageenan, A1), extracted from Agardhiella subulata (Rhodophyta), collected from Lake of Ganzirri (Italy), was evaluated for its effects on biofilm formation of the following fish pathogens relevant in aquacultures: Listonella anguillarum, Vibrio harveyi, V. parahaemolyticus and Photobacterium damselae subsp. piscicida, and human pathogens Pseudomonas aeruginosa and Staphylococcus aureus. All bacterial strains produced biofilms on polystyrene surfaces with different capabilities. A1 showed dose-dependent (50-400 μg/mL) inhibitory activity on the biofilm formation without exerting antibacterial activity. At the highest concentration 400 μg/mL, A1 showed antibiofilm activity against V. harveyi (52.8%), S. aureus, (51.6%), P. piscicida (48%), P. aeruginosa (44.5%), and L. anguillarum (32.8%). As assessed by the surface coating assay and the microbial adhesion onto hydrocarbons, A1 was able to inhibit the bacterial adhesion to polystyrene surfaces and modify their cell-surface properties (charges/hydrophobicity). Furthermore, A1 showed high emulsifying activity (E24 up to 70%). The results suggested that the algal extract, due to surfactant and antiadhesive properties, hindered the first phases of the biofilm formation. Moreover, based on different toxicity assays, using Artemia salina and Danio rerio, and bioluminescence assay with V. harveyi (G5), A1 was not toxic indicating its safety and potential use for marine environmental applications. As a non-biocide, non-toxic, and biodegradable polysaccharide, with surfactant and antiadhesive properties, could be proposed to design and develop biofilm control measures in aquaculture and as an eco-friendly alternative to chemical anti-fouling substances.