Poster (download) Tatyana Vladimirovna Butina1, Yurij Sergeevich Bukin2, Igor Veniaminovich Khanaev31Laboratory of Analytical and Bioorganic Chemistry LIN SB RAS Irkutsk, Russia, tvbutina@mail.ru2Laboratory of Genosystematics LIN SB RAS Irkutsk, Russia, bukinyura@mail.ru3Laboratory of Ichthyology LIN SB RAS Irkutsk, Russia, igkhan@lin.irk.ru Sponges are the oldest multicellular invertebrates (phylum Porifera); they are ecologically important components of marine and freshwater benthic environments. Associated communities of sponges include a variety of microorganisms: fungi, algae, archaea, bacteria and viruses. The aim of this study was to elucidate the genetic diversity of viruses in the community of Baikal endemic sponges Baikalospongia bacillifera using metagenomic approach. We have shown for the first time a high genetic, potential taxonomic and functional diversity of dsDNA viruses in these Baikal sponges. Identified viral sequences belonged to 28 viral families that infect a wide range of organisms. The bacteriophages of the Myoviridae, Siphoviridae and Podoviridae families dominated in the samples. The viruses of the Phycodnaviridae, Poxviridae Mimiviridae, Herpesviridae, Baculoviridae, Polydnaviridae and Iridoviridae families were also the most numerous. Viral communities of visually healthy and diseased Baikal sponges were significantly different. Analysis of viral sequences has indicated 22 functional categories of proteins and revealed a wide variety of structural viral proteins and enzymes. Among those the genes of proteins involved in the metabolism of host cells were also identified. Thus, the role of viruses in sponges may be both in the regulation of the number and diversity and in the maintenance of the vital activity of their hosts and the associated community as a whole.