| No water, no life. It is necessary to pay attention to water environment and ecological condition. Therefore, we studied the virioplankton of Lake Donghu, including several contents: 1. study on mophological diversity of virioplankton; 2. the spatial and temporal distribution of virioplankton in Lake Donghu; 3. study on genome size virioplankton; 4. the isolation of bacteriophages. The main results are given as follows: 1. The morphological diversity of virioplankton was studied by transmoission electron microscope (TEM) in station 6, 7and 8 located in center of Shuiguohu, Guozhenghu and Tanglinhu of Lake Donghu respectively. 76 species viruses with approximately spherical heads were observed, including 26 species virioplankers of Siphoviridae, 27 species virioplankters of Myoviridae, 12 species virioplankters of Podoviridae, 2 species virioplankters of Tectiviridae, 2 species virioplankters of Cystoviridae, 2 species virioplankters of Fuselloviridae, a species virioplankton of Corticoviridae and 4 species other mophological viruses. In addition, some Filovirus, Baculovirus, bullet-shaped and pleomorphic virioplankton were also observed. These results showed that most virioplankters were bacteriophages and cyanophages in Lake Donghu. 2. The distribution of virioplankton was measured in 8 stations of Lake Donghu by TEM. According to capsid diameter, virioplankters of Lake Donghu were separated into four groups < 30 nm, 30-60 nm, 60-80 nm, > 80 nm. The most abundant size class was the 30–60 nm group. The percentages of tailed virioplankton three center stations all closed to 50%, but at other stations ,tailed virioplankters only account for 14.41-31.11%, showing that there were many eukaryotic viruses accompanying wasterwater input in these stations. In 8 stations, virioplankton abundances ranged from 7.68 ×108 ml-1 to 3.03 ×109 ml-1, with a mean of 1.72 ×109 ml-1, which are among the highest reported for any natural aquatic environment to date. Virioplankton abundances were revealed highest numbers in stations located near the bank and lowest numbers in the three center stations. Among three center stations, two stations located in hypereutrophic and eutrophic regions were significantly higher than those of mesotrophic region. Virioplankton abundances of stations located near wastewater mouth were significantly lower than those of stations located about 55m away from the bank, but higher than those of center stations. These results showed that the distribution of virioplankton of Lake Donghu may related to trophic level of water envirioment and wasterwater input . 3. During July 2003 to June 2004, virioplankton abundance and viral population structure were measured in station 6, 7 and 8. the dominant virioplankton group was 30-60 nm, about 62% in all three stations. The frequencies of tailed virioplankton were all close to 50% in three sampled stations. The frequency distribution of viral capsid diameters and tailed viruses did not change significantly with season in the study During the one year, virioplankton abundances in three sampled stations were higher in spring than that in other seasons, and the lowest virioplankton enumeration were observed in winter. Virioplankton and chlorophyll a showed significant correlation, suggest that many virioplankters were produced by phytoplankton 4. Genome size of virioplankton was detected by pulsed field gel electrophoresis (PFGE) in Lake Donghu during March 2005. The genome size of virioplankton ranged from 15 to 300kb, Genome size of most virioplankters belonged to 20-60 kb. Five nucleic acid bands were observed, being 20 kb, 50 kb, 100 kb, 150 kb and 250 kb respectively. 5. Two bacteriophages (P1 and P2) belonging to Podoviridae were isolated from guozhenghu. P1 is virulent bacteriophage, with 128 nm head size and 28 nm tail length. P2 is temperate bacteriophage, with 125 nm head size and 24 nm tail length.
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