Marine Algal Viruses: Review of Phycovirus and Cyanophage Biology and Ecological Significance

Viruses specific to marine eukaryotic algae (phycoviruses) and cyanobacteria (cyanophages) are now recognised as ubiquitous in the world’s oceans and specificity has been determined for many species of both microand macroalgae. Algae have evolved mechanical, chemical and genetic defences against infection, however viruses potentially regulate several metabolic processes in marine plants. Virus-induced physiological damage results in changes to the biomass, photosynthetic and nutrient uptake rates in both microand macroalgae. Use of lysis products resulting from viral infection is potentially an important nutrition of marine plants in oligotrophic systems. Viral infection may adversely effect the reproductive capability of both microand macroalgae, by causing lysis of mature cells and gametophytes, respectively. Toxin production by marine cyanobacteria may be dependant on lysogeny by temperate phages. Viruses potentially influence community composition in mixedalgal populations, and have been shown to be responsible for the termination of algal blooms. Marine phycoviruses are genetically diverse in terms of gene sequence and genome size, however their morphology is similar. The distribution of phycoviruses in marine environments strongly reflects that of hosts. The use of phycoviruses in tracking harmful algal blooms and the use of algal chemical defences in preventing or treating human disease represent promising areas of future research.