Cyanophages

Abstract

Summary: Cyanophages, phages that infect cyanobacteria, are amongst the most abundant biological entities on the planet. They exert profound influences on the community structures of their hosts and on the biogeochemical cycles in which their hosts participate. Indeed, some cyanophages may directly contribute to the carbon cycle by a viral form of photosynthesis. The impact of cyanophages on natural populations has several dimensions. Cyanophages may cause population collapses, but where standing stocks are maintained cyanophages may influence genetic diversity and strain succession. The relationship is reciprocal and changes in host diversity will feedback into fluctuations in phage diversity. It is not clear yet to what extent phage infection competes with protistan grazing as the two major biotic causes of cyanobacterial mortality, but it is becoming apparent that there are subtle interactions between these two processes. This is in part related to the potential ability of cyanophages to alter the phenotype of the infected cell, not only via lysogeny, but also during the normal lytic infection cycle and during pseudolysogeny. Genomic analysis of cyanophages is revealing the extent to which cyanophages can modify the metabolism of the host cell via the acquisition of host-derived genes such as those involved in photosynthesis, carbon metabolism and nutrient acquisition.