Wilson, W.H. and Mann, N.H.
Department of Biological Sciences, University of Warwick, Coventry, CV4 7AL, U.K.
Investigations in the last six years have indicated the presence of high concentrations of viruses in seawater. It has been suggested that viruses may be more sensitive to phosphorus limitation than nitrate limitation since viruses have a high nucleic acid to protein ratio. A mesocosm was set up, in a Norwegian fjord, during June 1995 which contained 2 ‘phosphate-limited’ enclosures. Phosphate was added back to these enclosures after 3 weeks ‘limitation’. The main objective of this study was to determine the effect of phosphate status in these enclosures on virus production. A phycoerythrin-containing Synechococcus spp. bloom was observed in one of the ‘phosphate-limited’ enclosures. The effect of viruses on this bloom will be discussed. TEM analysis was used to estimate total virus-like particle (VLP) concentrations. A sharp rise in VLPs were observed after phosphate was added back to the ‘phosphate-limited’ enclosures. Phytoplankton were concentrated from 50 L volumes from each of the enclosures by tangential flow filtration (0.3 µm cut off), before and after phosphate addition. Preliminary results obtained by SDS-PAGE and western analysis on these concentrates, using polyclonal antibodies raised against a marine cyanophage, indicate that viral proteins present in the cellular fraction during ‘phosphate-limitation’ disappear when phosphate is added back to the enclosures. These results are consistent with viruses establishing some sort of psuedo-lysogenic response during phosphate-limitation, hence inhibiting virus production.
