2). For the phylogenetic analysis, different T4-type phages and g23 clones of marine and terrestrial environments from referred marine and paddy T4 subgroups (Filée et al., 2005; Wang et al., 2009a, b) Z-VAD-FMK clinical trial including the closest relative clones were used. The Bayesian tree obtained in our study is shown in Fig. 3. Our results revealed that neither of the Lake Baikal sequences was grouped into T-evens, PseudoT-evens or SchizoT-evens. The majority of g23 clones from Lake Baikal formed nine deep-branching clusters (B1–B9) with reliable support (79–100%). Two Lake Baikal clusters (B3 and B4) belonged to the ExoT-evens group of marine cyanophages. Clusters B1, B5 and four separate Lake Baikal clones

were grouped with marine or paddy soil T4 subgroups

(Marine groups III, IV; Paddy groups III, VI, VII). The rest of the Baikalian clusters (B2, B6–B9) were separate and the accessory of these clusters to any referred T4-type phage subgroups has not been determined. The most unique sequence found in our study was a clone S0508/1-1. It was clustered with two clones from Japanese paddy fields (KuCf-Jun12-17 and Ch-Cf-Sep22-11) obtained by Wang et al. (2009a). Apparently, this Ixazomib datasheet sequence had originated from an ancestor other than Lake Baikal phage sequences (Fig. 3). In this study, we analyzed the diversity of the T4-type bacteriophages in Northern and Southern Baikal using a PCR strategy based on the partial sequencing Reverse transcriptase of the g23 gene. We also compared these data with the composition and abundance of autotrophic picocyanobacteria and heterotrophic bacteria that are the most probable hosts for T4-like phages. We found that the populations of both bacterial and autotrophic plankton in Northern and Southern Baikal basins were significantly different. Northern Baikal was characterized by a high level of picocyanobacterial development. In contrast to this basin, the predominant numbers of heterotrophic bacteria were registered in Southern Baikal. The differences

in phytoplankton biomass were also recorded, and so the abundance of phytoplankton in Southern Baikal was much higher (Sakirko et al., 2009). Our study showed differences between the sequences of the T4 g23 gene obtained from Northern and Southern Baikal. Five Lake Baikal clusters (B1–B4, B7) were mainly composed of clones from the Northern basin while B5, B6 and B8 generally included clones from the Southern basin. Recently, Sandaa & Larsen (2006) demonstrated pronounced seasonal dynamics of the viral populations in Norwegian coastal waters and showed its correlation with the changes in the abundance of possible hosts. Following from this, we supposed that the biodiversity and quantity of bacterial plankton, autotrophic plankton and phytoplankton in two basins of Lake Baikal have determined a structure of viral communities in general and T4 bacteriophages in particular.