Promoting the simultaneous removal of Microcystis bloom and microcystin-RR by Bacillus sp. AK3 immobilized on floating porous glass pellets

Abstract

Harmful cyanobacterial blooms are global pollution problems. Algicidal bacteria, an effective method to control cyanobacteria that is widely studied in the laboratory, is often less effective when used in natural environments. A bacterium Bacillus sp. AK3, which has algicidal and microcystin-RR (MC-RR) degradation abilities, was used in this study. We determined the efficacy of Bacillus sp. AK3 in removing Microcystis sp. AARL C028 and MC-RR under laboratory conditions. Based on the results, Bacillus sp. AK3 can remove 100% of Microcystis sp. AARL C028 and 73% of extracted-MC-RR within 3 days, respectively. To improve the application of bacteria under natural cyanobacterial bloom conditions, floating porous glass pellets (FPGPs) were synthesized to serve as supporting material for bacterial immobilization. Based on SEM images, Bacillus sp. AK3 cells adhered to the surface of FPGPs by the action of the bacterial extracellular matrix. Bacillus sp. AK3 immobilized on FPGPs exhibited a higher algicidal efficiency than freely suspended cells. Under natural Microcystis spp. bloom conditions, the FPGPs can maintain the bacterial cells attached on their surface at around 19 × 107 CFU g−1. Bacillus sp. AK3 immobilized on FPGPs can reduce Microcystis spp. cells, chlorophyll-a content, and MC-RR by 82, 80, and 72%, respectively, within 8 days. The buoyancy of the FPGPs promotes contact between immobilized bacteria and cyanobacterial blooms floating on the water surfaces and facilitates re-collection.