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

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, ecofriendly 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.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study evaluated the algicidal potential of Paebubacillus sp. A9 against Microcystis aeruginosa and found that certain fractions of A9 exhibited algicidal activity. A9 induced flocculation of algal cells and subsequently lysed the cells through the release of algicidal compounds in the culture. The algicidal process activated the antioxidant system of M. aeruginosa and resulted in damage to the photosynthetic system. Inoculation with 6% A9 culture reduced the concentration of microcystin-LR (MC-LR) by 90.65%. Therefore, Paebubacillus sp. A9 may be a potential candidate for controlling M. aeruginosa-induced cyanobacterial harmful algal blooms through a flocculation-lysis-degradation mechanism and nutrient regulation.