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Aquatic Microbial Ecology

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AME 11:65-77 (1996)  -  doi:10.3354/ame011065

Cycling of marine dissolved organic matter. I. An experimental system

Zweifel UL, Blackburn N, Hagström Å

The degradation of dissolved organic carbon (DOC), together with bacterial growth and mortality, was studied in a multi-stage flow-through system. Particle-free sterile seawater was used as growth substrate and fed into vessels containing bacteria and viruses with or without flagellates. The residence time spanned from 30 to 1800 h. The rate of net organic carbon consumption decreased 3 orders of magnitude with increasing residence time (from 0.45 to 0.001 μM C h-1). Interestingly, we found a significantly higher DOC consumption in the presence of flagellates (1.3 to 10 times higher). Viruses were abundant in all culture vessels (1.7 to 6.5 × 1010 l-1), indicating active virus production within the system. The number of nucleoid-containing bacteria decreased with increasing residence time from 68% of the total count at the shortest residence time to 30% at the longest residence time. Also, with bacteria only, the total number of bacteria decreased at the longest residence time. We argue that with a long residence time the internal cycling of organic matter increased and that the fraction of viable bacteria decreased substantially resulting in a large fraction of 'ghosts'.

DOM · Degradation · Bacteria · Viability · Remineralization · Virus

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