A new nucleic acid stain, SYBR Green I, can be used for the rapid and accurate determination of viral and bacterial abundances in diverse marine samples. We tested this stain with formalinpreserved samples of coastal water and also from depth profiles (to 800 m) from sites 19 and 190 km offshore, by filtering a few m1 onto 0.02 pm pore-size filters and staining for 15 min. Comparison of bacterial counts to those made with acridine orange (AO) and virus counts with those made by transmission electron microscopy (TEM) showed very strong correlations. Bacterial counts with A 0 and SYBR Green 1 were indistinguishable and almost perfectly correlated (r2 = 0.99). Virus counts ranged widely, from 0.03 to 15 X 10' virus ml-l. Virus counts by SYBR Green 1 were on the average higher than those made by TEM, and a SYBR Green 1 versus TEM plot yielded a regression slope of 1.28. The correlation between the two was very high with an value of 0.98. The precision of the SYBR Green I method was the same as that for TEM, with coefficients of variation of 2.9%. SYBR Green I stained viruses and bacteria are intensely stained and easy to distinguish from other particles with both older and newer generation epifluorescence microscopes. Detritus is generally not stained, unlike when the alternative dye YoPro I is used, so this approach may be suitable for sediments. SYBR Green I stained samples need no desalting or heating, can be fixed with formalin prior to filtration, the optimal staining time is 15 min (resulting in a total preparation time of less than 25 min), and counts can be easily performed at sea immediately after sampling. This method may facilitate incorporation of viral research into most aquatic microbiology laboratories.

Viruses are the most abundant biological organisms of the world's oceans. Viral infections are a substantial source of mortality in a range of organisms-including autotrophic and heterotrophic plankton-but their impact on the deep ocean and benthic biosphere is completely unknown. Here we report that viral production in deep-sea benthic ecosystems worldwide is extremely high, and that viral infections are responsible for the abatement of 80% of prokaryotic heterotrophic production. Virus-induced prokaryotic mortality increases with increasing water depth, and beneath a depth of 1,000 m nearly all of the prokaryotic heterotrophic production is transformed into organic detritus. The viral shunt, releasing on a global scale approximately 0.37-0.63 gigatonnes of carbon per year, is an essential source of labile organic detritus in the deep-sea ecosystems. This process sustains a high prokaryotic biomass and provides an important contribution to prokaryotic metabolism, allowing the system to cope with the severe organic resource limitation of deep-sea ecosystems. Our results indicate that viruses have an important role in global biogeochemical cycles, in deep-sea metabolism and the overall functioning of the largest ecosystem of our biosphere.

Mesocosms filled with 80 liters of coastal seawater

Sea-surface warming, sea-ice melting and related freshening, changes in circulation and mixing regimes, and ocean acidification induced by the present climate changes are modifying marine ecosystem structure and function and have the potential to alter the cycling of carbon and nutrients in surface oceans. Changing climate has direct and indirect consequences on marine viruses, including cascading effects on biogeochemical cycles, food webs, and the metabolic balance of the ocean. We discuss here a range of case studies of climate change and the potential consequences on virus function, viral assemblages and virus-host interactions. In turn, marine viruses influence directly and indirectly biogeochemical cycles, carbon sequestration capacity of the oceans and the gas exchange between the ocean surface and the atmosphere. We cannot yet predict whether the viruses will exacerbate or attenuate the magnitude of climate changes on marine ecosystems, but we provide evidence that marine viruses interact actively with the present climate change and are a key biotic component that is able to influence the oceans' feedback on climate change. Long-term and wide spatial-scale studies, and improved knowledge of host-virus dynamics in the world's oceans will permit the incorporation of the viral component into future ocean climate models and increase the accuracy of the predictions of the climate change impacts on the function of the oceans.

A nested-PCR method was used to detect the occurrence of human adenovirus in coastal waters of Southern California. Twenty-to forty-liter water samples were collected from 12 beach locations from Malibu to the border of Mexico between February and March 1999. All sampling sites were located at mouths of major rivers and creeks. Two ultrafiltration concentration methods, tangential flow filtration (TFF) and vortex flow filtration (VFF), were compared using six environmental samples. Human adenoviruses were detected in 4 of the 12 samples tested after nucleic acid extraction of VFF concentrates. The most probable number of adenoviral genomes ranged from 880 to 7,500 per liter of water. Coliphages were detected at all sites, with the concentration varying from 5.3 to 3332 PFU/liter of water. F-specific coliphages were found at 5 of the 12 sites, with the concentration ranging from 5.5 to 300 PFU/liter. The presence of human adenovirus was not significantly correlated with the concentration of coliphage (r ‫؍‬ 0.32) but was significantly correlated (r ‫؍‬ 0.99) with F-specific coliphage. The bacterial indicators (total coliforms, fecal coliforms, and enterococci) were found to exceed California recreational water quality daily limits at 5 of the 12 sites. However, this excess of bacterial indicators did not correlate with the presence of human adenoviruses in coastal waters. The results of this study call for both a reevaluation of our current recreational water quality standards to reflect the viral quality of recreational waters and monitoring of recreational waters for human viruses on a regular basis.