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Applied and Environmental Microbiology, August 2001, p. 3481-3487, Vol. 67, No. 8
Marine Environment Division, Environmental
Assessment Department, National Institute for Resources and
Environment, AIST, MITI, Tsukuba, Ibaraki 305-8569, Japan
Received 6 December 2000/Accepted 30 May 2001
Nitrate flux between sediment and water, nitrate concentration
profile at the sediment-water interface, and in situ sediment denitrification activity were measured seasonally at the innermost part
of Tokyo Bay, Japan. For the determination of sediment nitrate concentration, undisturbed sediment cores were sectioned into 5-mm
depth intervals and each segment was stored frozen at
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.8.3481-3487.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Presence of Nitrate-Accumulating Sulfur Bacteria
and Their Influence on Nitrogen Cycling in a Shallow Coastal
Marine Sediment
30°C. The
nitrate concentration was determined for the supernatants after
centrifuging the frozen and thawed sediments. Nitrate in the uppermost
sediment showed a remarkable seasonal change, and its seasonal maximum
of up to 400 µM was found in October. The directions of the diffusive
nitrate fluxes predicted from the interfacial concentration gradients
were out of the sediment throughout the year. In contrast, the
directions of the total nitrate fluxes measured by the whole-core
incubation were into the sediment at all seasons. This contradiction
between directions indicates that a large part of the nitrate pool
extracted from the frozen surface sediments is not a pore water
constituent, and preliminary examinations demonstrated that the nitrate
was contained in the intracellular vacuoles of filamentous sulfur
bacteria dwelling on or in the surface sediment. Based on the
comparison between in situ sediment denitrification activity and total
nitrate flux, it is suggested that intracellular nitrate cannot be
directly utilized by sediment denitrification, and the probable fate of
the intracellular nitrate is hypothesized to be dissimilatory reduction
to ammonium. The presence of nitrate-accumulating sulfur bacteria
therefore may lower nature's self-purification capacity
(denitrification) and exacerbate eutrophication in shallow coastal
marine environments.
*
Mailing address: Marine Environment Division,
Environmental Assessment Department, National Institute for Resources
and Environment, AIST, MITI, 16-3 Onogawa, Tsukuba, Ibaraki 305-8569, Japan. Phone: 81-298-61-8375. Fax: 81-298-61-8357. E-mail:
m.sayama{at}aist.go.jp.
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