8 Egypt. J. Bot. 2 nd International conference, 29-30 April, Minia Univ., pp. 113 س124 (2012) _________________________________________________________________________ *Correspondence author, E-mail: alimali@mu.edu.eg Mobile: 01224220938 Seasonality, Distribution and Host Range Analysis of Cyanophage Infected Phormidium orientale Ali M. Ali*, El-Naghy, M. A, El-Katatny, M. S. Soma, A. Badry Department of Botany and Microbiology, Faculty of Science, Minia University, El-Minia, Egypt. NOVEL VIRUS causing lysis of a culture of the cyanobacterium Phormidium orientale was isolated from the Rice field in El-Qalubia governorate, Egypt. The virus named Phormidium orientale virus Egypt-Rice 1 (POVE-R1) was isolated by liquid lysis and plate techniques. The widespread occurrence of the Rice field Phormidium virus was recorded in May and November 2010. Our results for screening of the virus in other three freshwater places in El-Minia Governorate showed that the virus was detected in El-Moheit drainage (May and August 2010), in Nile River (May 2010) and surprisingly not detected in El-Ibrahimia canal. Phormidium orientale virus was found to be very specific in its infection to Phormidium orientale and not infect any other Phormidium sp., Synechocystis sp. or Nostos sp. involved in this study. Keywords: Cyanophages, Phormidium, host range, Rice field. Virus ecology deals with the interaction of viruses with their host cells in the environment and the effects such interaction have on the composition and productivity of particular habitats. This field is still relatively new and many processes by which viruses influence hosts still widely unknown. To investigate and understand virus ecology, it is necessary to study the distribution, host range and seasonality of the viruses in the environment. Viruses are everywhere, most probably all organisms have viruses infecting them and viruses seem to have many hosts (Bamford et al., 2005a). In aquatic environments, the virus abundance have been observed to be higher than the host abundance whether these environments is a sea, a freshwater environment (Wommack and Colwell, 2000), or an environment with high salinity like the Dead sea (Oren et al., 1997). Viruses have not only been isolated from common environments such as oceans (Espejo and Conelo, 1968) and seawage (Olsen et al., 1974) but also from extreme conditions like hot springs (Jaatinen et al., 2008), fermented fish source (Paluing, 1982) and Arctic sea ice (Borriss et al., 2003). Many studies have indicated the ecological importance of viruses in global biogeochemical nutrient cycles (Weinbauer, 2004). Viruses are known to be an abundant and dynamic component in the aquatic microbial communities that can regulate the biomass production and species composition of varied microorganisms and other life forms like bacteria and phytoplankton (Singh et al., 2012). Cyanobacteria, also called blue-green algae, are photosynthetic prokaryotes that only require carbon dioxide, light and an inorganic substrate to survive. Most cyanobacteria have the potential to form blooms, with some producing considerable toxins during these events. The factors that control their abundance and diversity include temperature, nutrient availability, sinking, and mortality due to grazing and viral lysis. Viruses infected Cyanobacteria as hosts are called cyanophages. These cyanophages play an essential role in aquatic and global ecosystem. All cyanophages isolated from aquatic environments are A