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Viral infection of prokaryotic plankton during early formation of the North West Atlantic Deep Water

Markus G. Weinbauer*, Christian Griebler, Hendrik M. van Aken,Gerhard J. Herndl

*Corresponding author:

ABSTRACT: Viral abundance was assessed in different water masses of the NW Atlantic and the development of viral abundance, lytic viral infection and lysogeny was followed in the first ca. 5000 km (corresponding to ca. 50 yrs) of the western branch of the North Atlantic Deep Water (NADW) in the oceanic conveyor belt. Viral abundance was significantly higher in the 100m layer than in the NADW (2400-2700m depth) and the Denmark Strait Overflow Water (2400-3600m depth). The virus-to-prokaryote ratio (VPR) increased with depth ranging from 32-43 for different water masses of the bathypelagic ocean thus, corroborating the enigma of high viral abundance in the dark ocean. The O2-minimum layer (250-600m) showed also high viral abundances and VPRs. Viral abundance, a viral subgroup and VPRs decreased in a non-linear form with the distance from the NADW origin. Viral production (range, 0.2-2.4 x 107 viruses l-1) and the fraction of lytically infected cells (range, 1 to 22%) decreased with increasing distance from the formation site of the NADW. Conservative estimations of virus-mediated mortality of prokaryotes in the NADW averaged 20±12%. The fraction of the prokaryotic community with lysogens (harboring a functional viral DNA) in the NADW averaged 21±14%. Hence we conclude that 1) viral abundance and subgroups differed between water masses, 2) virus-mediated mortality of prokaryotes as well as lysogeny are significant in the dark ocean, and 3) the lysogenic life strategy becomes more important than the lytic life style during the early formation of the NADW.