Flocculation and lysis of Microcystis aeruginosa by Paebubacillus sp. A9 and inhibition of microcystin release

Abstract

Algae such as Microcystis aeruginosa, which are involved in cyanobacterial harmful algal blooms (CyanoHABs), pose a serious threat to aquatic organisms and human health, and have become a severe environmental problem. In the search for efficient, eco-friendly and safe approaches to control CyanoHABs, we evaluated the algicidal potential of Paebubacillus sp. A9 (A9) cells, supernatants and cultures with flocculation properties against M. aeruginosa. The results showed that different fractions of A9 exhibited algicidal activity in a dose- and time-dependent manner. Initially, polysaccharides with a series of carboxyl groups released by A9 caused flocculation of M. aeruginosa cells, which was followed by the lysis of algal cells by the algicidal active compounds present in the A9 culture. The algicidal process activated the antioxidant system of M. aeruginosa, as evidenced by a dramatic increase in the activities of catalase (CAT) and superoxide dismutase (SOD) enzyme. Simultaneously, photosynthetic pigments (Chl a), photosynthetic efficiency (Fv/Fm) and maximum relative photosynthetic electron transfer rate (ETRmax) were significantly decreased, indicating the impairment of the photosynthetic system of M. aeruginosa by A9 culture. Notably, inoculation with 6% A9 culture reduced the microcystin-LR (MC-LR) concentration by 90.65% compared to the control. Further analysis of fluorescent dissolved organic contaminants, disinfection by-product precursors, and nitrogen and phosphorus nutrients in the algal culture, confirmed the environmentally safety of the A9-mediated algicidal process. Therefore, Paebubacillus sp. A9 be a potential candidate for controlling M. aeruginosa-induced CyanoHABs through its ”flocculation–lysis–degradation” mechanism, coupled with nutrient regulation.