title: Evolving interactions between diazotrophic cyanobacterium and phage mediate nitrogen release and host competitive ability.
abstract: Interactions between nitrogen-fixing (i.e. diazotrophic) cyanobacteria and their viruses, cyanophages, can have large-scale ecosystem effects. These effects are mediated by temporal alterations in nutrient availability in aquatic systems owing to the release of nitrogen and carbon sources from cells lysed by phages, as well as by ecologically important changes in the diversity and fitness of cyanobacterial populations that evolve in the presence of phages. However, ecological and evolutionary feedbacks between phages and nitrogen-fixing cyanobacteria are still relative poorly understood. Here, we used an experimental evolution approach to test the effect of interactions between a common filamentous, nitrogen-fixing cyanobacterium (Nodulariasp.) and its phage on cellular nitrogen release and host properties. Ecological, community-level effects of phage-mediated nitrogen release were tested with a phytoplankton bioassay. We found that cyanobacterial nitrogen release increased significantly as a result of viral lysis, which was associated with enhanced growth of phytoplankton species in cell-free filtrates compared with phage-resistant host controls in which lysis and subsequent nutrient release did not occur after phage exposure. We also observed an ecologically important change among phage-evolved cyanobacteria with phage-resistant phenotypes, a short-filamentous morphotype with reduced buoyancy compared with the ancestral long-filamentous morphotype. Reduced buoyancy might decrease the ability of these morphotypes to compete for light compared with longer, more buoyant filaments. Together, these findings demonstrate the potential of cyanobacteria-phage interactions to affect ecosystem biogeochemical cycles and planktonic community dynamics.
authors.affiliation: Department of Food and Environmental Sciences/Microbiology and Biotechnology , University of Helsinki , PO Box 56, 00014 Helsinki , Finland.
authors.forename: Johannes
authors.identifier: 0000-0003-1329-2025
authors.initials: J
authors.lastname: Cairns
authors.affiliation: Department of Food and Environmental Sciences/Microbiology and Biotechnology , University of Helsinki , PO Box 56, 00014 Helsinki , Finland.
authors.forename: Sebastián
authors.initials: S
authors.lastname: Coloma
authors.affiliation: Department of Food and Environmental Sciences/Microbiology and Biotechnology , University of Helsinki , PO Box 56, 00014 Helsinki , Finland.
authors.forename: Kaarina
authors.initials: K
authors.lastname: Sivonen
authors.affiliation: Department of Food and Environmental Sciences/Microbiology and Biotechnology , University of Helsinki , PO Box 56, 00014 Helsinki , Finland.
authors.forename: Teppo
authors.identifier: 0000-0001-7206-2399
authors.initials: T
authors.lastname: Hiltunen
keywords: Nodularia sp.; cyanobacteria; cyanophages; eco-evolutionary dynamics; host–parasite interaction; marine nitrogen cycle