PHAGES INFECTING BLOOM-FORMING CYANOBACTERIA SHOW HIGH SEQUENCE AND PHENOTYPIC VARIABILITY

Bloom-forming cyanobacteria are an increasing global phenomenon that negatively impact aquatic environments worldwide. These blooms are comprised of multicellular cyanobacteria that form filaments or colonies. Both phages and eukaryotic grazers play a significant role in the top-down control of cyanobacteria. While there are eukaryotic grazers that have the potential to temporarily prevent cyanobacterial blooms or control their biomass, the role of phages in cyanobacteria bloom dynamics is poorly understood. In order to expand our knowledge of phages infecting bloom-forming cyanobacteria, we have isolated 15 cyanophages from Lake Kinneret (Israel), using Cylindrospermopsis raciborskii and Aphanizomenon ovalisporum as hosts. The host range of these phages varied from a single host to broad host range. Some phages infected both filamentous and unicellular strains. Electron microscopy imaging of the phages show they belong to siphoviridae and podoviridae families and differ by their tail and head morphologies (even within a family). Sequence analysis of a subset of the phages suggest that these phages are Lambda-like, although the genes shared by the different phages and Lambda vary, and there is no nucleotide or amino acid similarity between the newly isolated strains. Moreover, although approximately 85% of their genes have unknown function, many genes have high similarity to genes found in prophages, suggesting these phages may be lysogenic under different conditions or in other hosts than the ones we analyzed. The phenotypic and genotypic diversity of these phages, that were all isolated at the same time from the same location, suggest that phages infecting bloom-forming cyanobacteria are extremely diverse. Additionally, the various host range patterns and the sequence similarity to prophages suggest that these phages have multifaceted interactions with their hosts.