Effects of environment-relevant concentrations of antibiotics on seawater Chlorella sp. biofilm in artificial mariculture effluent

Abstract

Attached cultivation of microalgae using mariculture effluent could simultaneously realize cost-effective biomass production and effluent polishing, and the obtained microalgal biofilm could be readily applied to aquatic animals that feed directly on biofilms. However, the widespread existence of antibiotics in mariculture effluent may have inhibitory effects on microalgae. Existing studies regarding the influences of antibiotics on microalgae were overwhelmingly mostly conducted in suspended freshwater cultures, and the explored antibiotic concentrations were several orders of magnitudes higher than realist effluent, rendering limited guidance for practical applications. This study, therefore, studied three commonly observed antibiotics in mariculture effluent, i.e. sulfamethoxazole (SMX), tetracycline (TL), and clarithromycin (CLA), and explored their effects on attached seawater Chlorella sp. growth, nutrients removal, and antioxidative properties at environment-relevant concentrations (0.1–200 μg/L). Hormesis was shared among the three antibiotics, and highest biofilm density (14.6 g/m2) was observed under 0.1 μg/L SMX. SMX displayed strongest chlorophyll impairment, while SMX, TL, and CLA respectively favored lipid (up to 42.4 %), protein (up to 39.6 %), and polysaccharides (up to 65.4 %) accumulation. Highest correlation between biofilm density and extracellular polymeric substances (EPS) contents as well as highest total nitrogen (TN) removal were observed under TL exposure, while total phosphorus (TP) removal among all groups met the strictest local discharge standard for mariculture effluent (TP < 0.2 mg/L). Antioxidative responses revealed least stress towards attached seawater Chlorella sp. under TL treatment, while best acclimation under SMX exposure. Potential coping mechanisms of this microalgae under each antibiotic exposure were proposed as well. This study expands the knowledge of microalgae biofilm under environment-relevant concentrations of antibiotics.