Co-Occurrence of Toxic Bloom-Forming Cyanobacteria Planktothrix, Cyanophage, and Symbiotic Bacteria in Ohio Water Treatment Waste: Implications for Harmful Algal Bloom Management

Cyanobacterial blooms are increasingly becoming more intense and frequent, posing a public health threat globally. Drinking water treatment plants that rely on algal bloom-affected waters may create waste (water treatment residuals, WTRs) that concentrates contaminants. Source waters may contain harmful cyanobacteria, cyanophages (bacteriophages that infect cyanobacteria), and bacteria. Cyanophages are known to affect bloom formation and growth dynamics, so there is a need to understand viral-host dynamics between phage and bacteria in these ecosystems for managing cyanobacteria. This study isolated and characterized lytic cyanophages from WTRs of a HAB-affected lake in Ohio that infect toxic bloom-forming filamentous cyanobacteria <i>Planktothrix agardhii</i>. Phage infections in the Lake Erie cyanobacteria culture were examined visually and via microscopy and fluorometry. Whole genome sequencing and metagenomic analyses were also conducted. Observed changes in <i>Planktothrix</i> included sheared and shriveled filaments, reduced clumping, and buoyancy changes. Photosynthetic pigmentation was unexpectedly more apparent during phage infection. Metagenomic analyses identified nineteen phages and seven other co-existing bacterial genera. Annotated bacterial genomes contained metabolic pathways that may influence phage infection efficiency. Viral genomes were successfully tied to microbial hosts, and annotations identified important viral infection proteins. This study examines cyanobacterial-phage interactions that may have potential for bioremedial applications.