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Abstract

Batch cultures of natural bacterial communities were grown in filter-sterilized seawater
from coastal and open-ocean sites. Natural coastal seawater was supplemented with up to
500 μg/l of various nitrogen containing substrates like putrescine, cadaverine, glutamic acid,
serine and ammonia. The removal of these compounds was monitored by high performance
liquid chromatography. Increases in bacterial cell number during the batch culture were counted
with an epifluorescence microscope after acridine organe staining (AODC). All compounds were
removed from coastal seawater cultures within 48 hours with no corresponding increase in
bacterial yield or growth rate relative to control (unsupplemented) cultures. Shipboard experiments with open-ocean deep water (1500 m) showed similar results, but slower removal of
the added substrates from seawater. Indicators of metabolic activity such as glucose and glutamic
acid uptake and mineralization potentials per cell and ratio of colony forming units (CFU) to
total cell counts (AODC) increased markedly during the growth phase. This mixed culture
approach could therefore help estimate heterotrophic potentials of compounds that are difficult
to degrade over reasonable incubation times with natural bacterial communities and also
elucidate the biochemical fate of these compounds.