Freshwater cyanobacterial bloom formation has been identified as one of the major environmental issues across the globe. Cyanobacterial blooms risk human and animal health  due to exposure to cyanotoxins. Because of cyanobacterial complexity, the development of efficient and universal cyanobacterial control strategies is challenging. In Sri Lanka, cyanobacterial blooms are becoming an environmental issue and to provide a solution this study was designed to develop a bacteria-based formulation to control cyanobacterial blooms. The major concerns in the formulation development were efficient immobilization and survival of bacteria, targeted delivery, effective cyanobacteria degradation, and minimal impact on the  receiving environment. Four different lignocellulosic materials; corn husk, rice husk, rice straw, and sugarcane bagasse, along with a widely used bacterial carrier; sodium alginate, were selected as bacteria carriers. Bacteria immobilization was improved by alkaline treatment. All carrier materials were able to maintain high bacteria viability with >10⁷ colony forming units (CFU) per one gram of material up to 49 days of incubation. The impact of carrier materials on the quality of receiving water was assessed by measuring pH, electrical conductivity, salinity,  dissolved oxygen demand, turbidity, total dissolved solids, and chemical oxygen demand (COD). Except COD, the effect was minimal in waters that received sodium alginate and rice husk and in the favorable level according to the national water quality regulations. Hence, those  two materials were selected for formulation development. Previously characterized twenty-two  native bacterial strains with cyanolytic and cyanotoxin degradation were used for the screening. Their ability to form biofilms was tested and the risk of spreading antibiotic resistance were  assessed by calculating the Multiple Antibiotic Resistance (MAR) index. Finally, the antagonistic effect was tested to select suitable strains for forming consortia. The best  performing isolates with strong biofilm formation, non-antagonistic and having the lowest MAR  index were Exiguobacterium acetylicum KAW 7 and Pseudomonas sp. GIRI 4 strain. Both rice  husk and sodium alginate showed growth enhancement in the tested filamentous cyanobacteria;  Oscillatoria, Nostoc, and Pseudanabaena and colony-forming Microcystis. This may be due to the utilization of rice husk and sodium alginate carrier materials as a nutrient source by cyanobacteria. Therefore, further experiments were focused on talc powder as an inorganic, inert and non biodegradable carrier material. The impact of talc on the water quality was found minimal. The overall quality parameters were in the range of Ambient Water Quality Standard of National Environmental Regulations. Talc-based formulation made with KDM41 strain showed 3.6× 10⁷ CFU/g bacteria viability tested after 5 weeks of incubation, maintaining a  high shelf life. The talc based KDM41 bacteria formulation showed 35% of cell lysis of Microcystis; the mostly reported bloom forming cyanobacteria in Sri Lanka. This formulation also did not show any negative effect on non-targeted aquatic life tested with Lemna minor, Azolla sp. and Poecilia reticulate. These results highlight that talc is a promising alternative to organic carrier material to deliver cyanolytic bacteria to water. To the best of my knowledge, for the first time in Sri Lanka, this study reveals the potential of developing bacteria-based formulation to control  freshwater cyanobacterial blooms.

Keywords: Bacteria formulation, Bacterial Carriers, Cell Lysis, Talc, Water quality, Cyanolytic 
bacteria