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Bacterioplankton cell death: competition between flagellate grazing and viral lysis and the role of bacterioplankton cell wall-derived dissolved organic matter in the ocean (BADE)

Project leader: Prof.dr. G.J. Herndl

Financier: NWO Council for Earth and Life Sciences

The project focuses on the mechanisms regulating bacterioplankton death and the fate of refractory bacterioplankton-derived dissolved organic matter (DOM) in the oceanic water column. Based on preliminary experiments performed in our laboratories and on recent findings by other research groups there is evidence that bacteria might contribute more to the oceanic DOM pool than assumed hitherto. Particularly, we will focus on the role of the bacterioplankton capsule in regulating protist grazing and viral infection, the interaction between protist grazing, prophage induction and virus production and on the role of viral lysis on the release of cell wall-derived DOM. The cell wall derived DOM will be assessed by measuring peptidoglycan compounds and D-/L-amino acids characteristic for the bacterial cell wall. Measurements will be made in situ during cruises throughout the water column of the North Atlantic and the western Mediterranean Sea and in controlled laboratory experiments. The number of bacteria enumerating capsulated bacteria. This will allow us to determine the relation between metabolically active cells and the expression of a polysaccharide capsule. This technique is the basis to elucidate the role of the capsule in potentially regulating protist grazing and viral lysis. Furthermore, the protist- and viral-mediated production of dissolved peptidoglycan and the combined enantiomeric amino acids will be determined in laboratory experiments and compared with in situ concentrations of these compounds and its utilization in the different depth layers of the water column. This study will enable us to obtain a holistic view on the role of the polysaccharide capsule of bacterioplankton cells on predation by protests, viral infection and the formation mechanisms of refractory bacterial-derived DOM. Thus we will obtain a mechanistic understanding of the fate of this potentially important source of oceanic DOM and its major sinks.