Spatial and temporal distribution of virioplankton and bacterioplankton in a brackish environment (Lake of Ganzirri, Italy)

Temporal and spatial changes of viral and bacterial abundance were examined in relation to environmental factors and hydrography at five stations between May 2000 and July 2001 in the brackish lake of Ganzirri (Sicily, Italy). Virioplankton abundance ranged from 5.26 x 104 to 7.54 x 108 VLP ml-1 (on average 1.38 x 108 particles ml-1) and was significantly higher at the three eutrophic stations located in the lake of Ganzirri (Stations 1, 2, and 3) than in the channel connecting the lake with the Straits of Messina. The virus-to-bacterium abundance ratio (VBR range, 0.4–117; average: 14) showed the highest values in channel connecting the lake of Ganzirri with the meromictic lake of Faro. VBR values <1.0 were found in summer 2000 in relation with peculiar hydrographic constraints. Virioplankton distribution was dependent on salinity, and on dilution of the oligotrophic waters flowing from the Straits. Virioplankton was closely related with bacterioplankton indicating a close coupling between viruses and host cell abundance.