Kaori Ohki
Department of Marine Science, School of Marine Science and Technology, Tokai University, Shimizu, Shizuoka 424-8610 Japan.
Recent studies suggest that cyanophages (viruses which infect cyanobacteria) play an important ecological role in marine environments. However, most known cyanophages are virulent types which kill the host shortly after infection. We found that considerably large numbers of marine cyanobacteria of section III isolated from different areas harbored lysogenized cyanophages; complete cell lysis was induced within several days after addition of mitomycin C (1 µ g/ml) or a brief UV-illumination in 16 strains out of 28. Occurrence of phage particles in cells prior to lysis induced by mitomycin C was confirmed in three Phormidium strains, persicinum (Provacoli strain), NIBB 1044 and NIBB1048, and Trichodesmium sp. NIBB1067. Cyanophages isolated from these strains were different in morphology, restriction fragment patterns of DNA and immunological characteristics. Some fraction of phages were in the lytic cycle even under the normal growth conditions; the fraction of phages in the lytic cycle varied depending on many factors including the culture conditions of the host cells. The possible role of lysogenic cyanophages on cyanobacterial populations in marine environment will be discussed.