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Marine Ecology Progress Series

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MEPS 221:47-57 (2001)  -  doi:10.3354/meps221047

Population dynamics and diversity of phytoplankton, bacteria and viruses in a seawater enclosure

A. Larsen1,*, T. Castberg1, R. A. Sandaa1, C. P. D. Brussaard2, J. Egge3, M. Heldal1, A. Paulino3, R. Thyrhaug1, E. J. van Hannen4, G. Bratbak1

1Department of Microbiology, University of Bergen, Jahnebakken 5, 5020 Bergen, Norway
2Department of Biological Oceanography, Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands
3Department of Fisheries and Marine Biology, University of Bergen, Bergen High Technology Centre, 5020 Bergen, Norway
4Department of Microbial Ecology, Centre for Limnology, Netherlands Institute of Ecology, PO Box 1299, 3600 BG Maarssen, The Netherlands

ABSTRACT: We now know that the abundance of free viruses in most marine environments is high. There is still, however, a lack of understanding of their occurrence and distribution and of in situ relationships between viral and host communities in natural environments. This may be partly due to methodological limitations. Our main aim was therefore to perform a case study in which a variety of methods were applied in order to give an improved, high-resolution description of the microbial communities in a natural environment. In order to do this we combined light microscopy (LM), transmission electron microscopy (TEM), flow cytometry (FCM), PCR denaturing gradient gel electrophoresis (PCR-DGGE) and pulsed-field gel electrophoresis (PFGE) and studied the diversity and succession of algae, bacteria and viruses in a nutrient enriched seawater enclosure. In the enclosure we experienced a situation where the development of the dominating algal population, which consisted of several flagellate species, was followed by proliferation of several different size-classes of viruses. The total bacterial number decreased markedly during the flagellate bloom but the community composition was maintained and the diversity remained high. Our results indicate a close linkage between various algal, bacterial and viral populations and show that virioplankton do not necessarily terminate algal and bacterial blooms but that they keep the host populations at non-blooming levels.

KEY WORDS: Bacteria · DGGE · Diversity · Flow cytometry · Light microscopy · PFGE · Phytoplankton · Virus

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