AME 27:103-110 (2002)  -  doi:10.3354/ame027103

Reconsidering transmission electron microscopy based estimates of viral infection of bacterio- plankton using conversion factors derived from natural communities

Markus G. Weinbauer1,*, Christian Winter2, Manfred G. Höfle1

1GBF - German Research Centre for Biotechnology, Department of Environmental Microbiology, Mascheroder Weg 1, 38124 Braunschweig, Germany
2Netherlands Institute for Sea Research (NIOZ), Department of Biological Oceanography, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands
*Present address: Laboratoire d¹Océanographie de Villefranche (LOV), PB 28, 06234 Villefranche, France. E-mail:

ABSTRACT: The frequency of virus infected bacterial cells (FIC) was estimated in surface waters of the Mediterranean Sea, the Baltic Sea and the North Sea using the frequency of visibly infected cells (FVIC) as determined by transmission electron microscopy (TEM) and published average conversion factors (average 5.42, range 3.7 to 7.14) to relate FVIC to FIC. A virus dilution approach was used to obtain an independent estimation of FIC in bacterioplankton, and we provide evidence for the reliability of this approach. Across all investigated environments, FIC ranged from 2.4 to 43.4%. FIC data using both approaches were well correlated; however, the values were higher using the virus dilution approach. This indicates that the TEM approach has the potential to reveal spatiotemporal trends of viral infection; however, it may underestimate the significance of viral infection of bacteria when average conversion factors are used. Using data from the virus dilution approach and the TEM approach, we calculated new conversion factors for relating FVIC to FIC (average 7.11, range 4.34 to 10.78). Virally caused mortality of bacteria estimated from published FVIC data of marine and freshwater systems and using the new conversion factors ranged from not detectable to 129%, thus confirming that viral infection is a significant and spatiotemporally variable cause of bacterial cell death.

KEY WORDS: Phage · Virus · Mortality · Lysogeny · Latent period

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