Toxicity of the antiparasitic lipopeptide biosurfactant SPH6 to green algae, cyanobacteria, crustaceans and zebrafish

A lipopeptide with biosurfactant properties produced by the bacterium Pseudomonas H6 (SPH6) has antiparasitic effects and may serve as an alternative to chemotherapeutants against aquatic pathogens in aquaculture. We have elucidated its ecotoxicological potential by short-term standardized tests, including a growth rate inhibition test with algae (Raphidocelis subcapitata), a lethality test on the cyanobacteria Phormidium autumnale, a lethality test using crustaceans (Daphnia magna), a fish embryo acute toxicity test and a fish acute toxicity test using zebrafish (Danio rerio). The decrease of the biosurfactant concentration in zebrafish test water during 24 h was measured. The toxicity for crustaceans was highest (LC₅₀ = 20 mg/L), followed by the test with the zebrafish embryo (LC₅₀ = 27 mg/L). The juvenile zebrafish fish (complete mortality occurred between 40 and 80 mg/L), the cyanobacteria (LC₅₀ = 80 mg/L) and the green algae (EC₅₀ = 170 mg/L) showed higher tolerance. The determination of SPH6 concentrations in fish tank (up to 50 % elimination over 24 h) suggested that the compound may become adsorbed to tank walls, absorbed by fish or degraded. Further studies should determine its impact under different environmental settings (e.g. temperature) relevant for different branches of the aquaculture sector.