Contribution of virus-induced lysis and protozoan grazing to benthic bacterial mortality estimated simultaneously in microcosms

Ulrike R. Fischer, Claudia Wieltschnig, Alexander K.T. Kirschner, Branko Velimirov*

*Corresponding author for this work

Research output: Journal article (peer-reviewed)Journal article

34 Citations (Scopus)


In contrast to the water column, the fate of bacterial production in freshwater sediments is still a matter of debate. Thus, the importance of virus-induced lysis and protozoan grazing of bacteria was investigated for the first time simultaneously in a silty sediment layer of a mesotrophic oxbow lake. Microcosms were installed in the laboratory in order to study the dynamics of these processes over 15 days. All microbial and physicochemical parameters showed acceptable resemblance to field data observed during a concomitant in situ study, and similar conclusions can be drawn with respect to the quantitative impact of viruses and protozoa on the bacterial compartment. Viral decay rates ranged from undetectable to 0.078 h-1 (average, 0.033 h-1), and the control of bacterial production from below the detection limit to 36% (average, 12%). The contribution of virus-induced lysis of bacteria to the dissolved organic matter pool as well as to benthic bacterial nutrition was low. Ingestion rates of protozoan grazers ranged from undetectable to 24.7 bacteria per heterotrophic nanoflagellate (HNF) per hour (average, 4.8 bacteria HNF-1 h-1) and from undetectable to 73.3 bacteria per ciliate per hour (average, 11.2 bacteria ciliate-1 h-1). Heterotrophic nanoflagellate and ciliates together cropped up to 5% (average, 1%) of bacterial production. The viral impact on bacteria prevailed over protozoan grazing by a factor of 2.5-19.9 (average, 9.5). In sum, these factors together removed up to 36% (average, 12%) of bacterial production. The high number of correlations between viral and protozoan parameters is discussed in view of a possible relationship between virus removal and the presence of protozoan grazers.

Original languageEnglish
Pages (from-to)1394-1407
Number of pages14
JournalEnvironmental Microbiology
Issue number8
Publication statusPublished - Aug 2006
Externally publishedYes

ASJC Scopus subject areas

  • Microbiology
  • Ecology, Evolution, Behavior and Systematics


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