AQUATIC MICROBIAL ECOLOGY Aquat Microb Ecol Vol. 51: 13–21, 2008 doi: 10.3354/ame01183 Published April 24 INTRODUCTION Viruses are key components of aquatic ecosystems that affect material and energy flow through food webs and may influence species succession and community composition. Although viruses infecting freshwater Cyanobacteria were isolated as early as the 1960s (Safferman & Morris 1963), aquatic ecolo- gists paid little attention to these phytoplankton para- sites until high abundances of viruses were reported in a variety of aquatic environments (Torrella & Morita 1979, Bergh et al. 1989, Proctor & Fuhrman 1990). Since then, ongoing work has consistently demon- strated that viruses are abundant, diverse, and active members of marine and freshwater ecosystems, and there are many excellent reviews of the aquatic virus literature (Fuhrman 1999, Wilhelm & Suttle 1999, Wommack & Colwell 2000, Brussaard 2004, Suttle 2005). Early studies of virus-like particles in freshwater environments demonstrated that they were most abun- dant in eutrophic lakes (Bergh et al. 1989), were detectable in an ultra-oligotrophic lake (Klut & Stock- ner 1990), and their abundance was positively related to chlorophyll a concentration, bacterial abundance, bacterial production, and lake trophic status (Maranger & Bird 1995). Subsequent work has, for the most part, corroborated these findings and demon- strated that viruses are present in diverse freshwater environments including rivers (Farnell-Jackson & Ward 2003), Antarctic lakes of varying salinity (Lay- bourn-Parry et al. 2001), meromictic lakes (Jacquet et al. 2005), an alkaline hypersaline lake (Jiang et al. 2004), oligotrophic lakes (Klut & Stockner 1990, Vrede et al. 2003), mesotrophic lakes (Hennes & Simon 1995, Wilhelm & Smith 2000), and eutrophic lakes and reser- voirs (Fischer & Velimirov 2002, Weinbauer et al. 2003). Despite this growing body of knowledge of © Inter-Research 2008 · www.int-res.com *Email: steven.short@utoronto.ca Diversity of algal viruses in various North American freshwater environments Steven M. Short*, Cindy M. Short Department of Biology, University of Toronto Mississauga, 3359 Mississauga Road North, Mississauga, Ontario L5L 1C6, Canada ABSTRACT: To examine algal virus (Phycodnaviridae) genetic diversity in freshwater environments, gene fragments were cloned and sequenced from a river and a reservoir in Colorado, USA, and 2 dif- ferent lakes in Ontario, Canada using PCR methods that target a diverse subset of known Phycod- naviridae DNA polymerase genes. Numerous phycodnavirus gene sequences were obtained from every sample, and rarefaction analysis of the sequence libraries demonstrated that virus richness was variable among different sample locations, and among samples collected from the same location at different times. Phylogenetic analysis of the unique sequences from each sample indicated that most sequences from the same geographic region (i.e. Colorado or Ontario) clustered together, but several exceptions were also observed. Phylogenetic analysis also demonstrated that the sequences obtained were more closely related to sequences from cultivated marine phycodnaviruses belonging to the genus Prasinovirus than to those from cultivated freshwater phycodnaviruses from the genus Chlorovirus. Overall, phycodnavirus sequences originating from cultivated marine viruses and marine clone libraries were not genetically distinct from the freshwater phycodnavirus sequences reported in this study. KEY WORDS: Phycodnaviridae · Algal viruses · DNA polymerase · Diversity · Phylogeny Resale or republication not permitted without written consent of the publisher