In dilution cultures, marine planktonic Archaea are subject to mortality due to viral lysis. It has been shown that the frequency of lysogenized bacterial cells increases with depth and that marine Archaea constitute a numerically dominant group in the meso- and bathypelagic zone. These recent findings serve as the motivation for the proposed project, which is addressing the lack of knowledge on the functional role of planktonic Archaea in the meso- and bathypelagic zone by studying the relationship to thei r viruses.
The first objective is to determine the phylogenetic affiliation (Bacteria, Euryarchaeota, Crenarchaeota) of the lysogenized cells and to determine changes over depth. Objective one will be tackled by using a virus-dilution approach to measure t he fraction of lysogenized prokaryotic cells in combination with catalysed reporter deposition fluorescence in situ hybridisation (CARD-FISH) to determine the phylogenetic affiliation of the bacterial cells.
The second objective is to determine the dynamic s of dominant populations of lytic and lysogenic viruses and their hosts over depth and across seasons in relation to total virio- and bacterioplankton community composition. This will be achieved by using population specific virioplankton probes, prepared by randomly amplified polymorphic DNA polymerase chain reaction (RAPD-PCR). Subsequently, these probes will be used to identify dominant populations of lytic and lysogenic viruses by pulsed-field gel electrophoresis (PFGE) and hybridization analysis. Upon infection, lysogenic viruses integrate their genome into the genome of the host.
Thus, it will also be possible to track the populations of lysogenized prokaryotes. The third objective is to determine the partial nucleotide sequences of the genomes of dominant lysogenic viruses by cloning and sequencing to assess the phylogenetic affiliation of these lysogenic viruses. For the first time, archaeal viruses and their hosts will be studied in a pelagic system.
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