1. ¹Department of Biological Oceanography, Royal Netherlands Institute for Sea Research, Texel, The Netherlands
2. ²Laboratoire d'Océanographie de Villefranche, Université Pierre et Marie Curie Paris VI, UMR 7093, Villefranche-sur-Mer, France

Correspondence: GJ Herndl, Department of Biological Oceanography, Royal Netherlands Institute for Sea Research, PO Box 59, AB 1790 Den Burg, Texel, The Netherlands. E-mail: herndl@nioz.nl

Received 13 March 2008; Revised 13 May 2008; Accepted 15 May 2008; Published online 12 June 2008.

Abstract

Viral diversity has been studied in a variety of marine habitats and spatial and seasonal changes have been documented. Most of the bacteriophages are considered host specific and are thought to affect fast growing prokaryotic phylotypes more than slow growing ones. We hypothesized that viral infection and consequently, lysis occurs in pulses with only a few prokaryotic phylotypes lysed at any given time. Thus, we propose that the newly produced viruses represent only a fraction of the viral diversity present at any given time. Virioplankton diversity was assessed by pulsed-field gel electrophoresis in the surface waters of three distinct areas of the North Sea during the spring and summer. Bulk virioplankton diversity was fairly stable in these waters. Viral diversity produced by the indigenous bacterioplankton, however, exhibited day-to-day variability with only a few bands produced at any given time. These bands frequently matched bands of the in situ virioplankton; however, bands not present in the band pattern of the in situ virioplankton community were also found. These new bands probably indicate infection and subsequent release of viruses from bacterioplankton phylotypes previously not infected by these specific viruses. Overall, our results demonstrate that viral infection and lysis are rather dynamic processes. The main targets of viral infection are changing apparently on time scales of hours to days indicating that viral infection might effectively regulate and maintain bacterioplankton diversity.