Distribution of viruses and bacteria in relation to diagenetic activity in an estuarine sediment

The distribution of viruses and bacteria was investigated in relation to bacterial sulfate reduction and total respiration (production of dissolved inorganic carbon, [DIC]) in a coastal sediment. Viral and bacterial abundance ranged from about 0.5 X 10(8) to 8 X 10(8) viruses cm(-3) and 0.1 X 10(8) to 4 X 10(8) bacteria cm(-3) in the upper 16 cm of the sediment and showed large and systematic changes within scales of a few centimeters. In general, viral abundance was highest in the sediment surface (0-1 em); however subsurface peaks at 3-5 cm depth associated with increased diagenetic activity were also observed. The virus-bacterium ratio ranged from 1.4 to 7.8 and increased significantly with depth in the upper 6 cm (P <0.001). Viral abundance showed significant positive correlation with both bacterial abundance and activity (P much less than 0.001), suggesting that the distribution and abundance of viruses were closely coupled to the activity of the bacterial community and that viruses are produced by bacteria within the sediment. The significant coupling between viral abundance and sulfate reduction rate and DIC production is the first indication of viral production associated with diagenetic active bacteria in marine sediments. This coupling between viral abundance and bacterial activity and the distinct pattern of vertical distribution show that viruses are a dynamic component of the benthic community. The morphological analysis indicated that interstitial viral communities were dominated by long (>1 mum) filamentous forms with a helical symmetry. Several types of these filamentous forms were observed, as well as a variety of tailed forms with icosahedral symmetry. Filamentous forms are rarely found in the water column, which suggests that they are adapted to the benthic environment and specific to the interstitial hosts.