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Applied and Environmental Microbiology, August 2000, p. 3592-3602, Vol. 66, No. 8
Molecular Ecology
Group1 and Department of
Biogeochemistry,2 Max Planck Institute for
Marine Microbiology, 28359 Bremen, Germany
Received 8 March 2000/Accepted 16 May 2000
The community structure of sulfate-reducing bacteria (SRB) of a
marine Arctic sediment (Smeerenburgfjorden, Svalbard) was characterized by both fluorescence in situ hybridization (FISH) and
rRNA slot blot hybridization by using group- and genus-specific 16S
rRNA-targeted oligonucleotide probes. The SRB community was dominated
by members of the Desulfosarcina-Desulfococcus group. This
group accounted for up to 73% of the SRB detected and up to 70% of
the SRB rRNA detected. The predominance was shown to be a common
feature for different stations along the coast of Svalbard. In a
top-to-bottom approach we aimed to further resolve the composition of
this large group of SRB by using probes for cultivated genera. While
this approach failed, directed cloning of probe-targeted genes encoding
16S rRNA was successful and resulted in sequences which were all
affiliated with the Desulfosarcina-Desulfococcus group. A
group of clone sequences (group SVAL1) most closely related to
Desulfosarcina variabilis (91.2% sequence similarity) was
dominant and was shown to be most abundant in situ, accounting for up
to 54.8% of the total SRB detected. A comparison of the two methods used for quantification showed that FISH and rRNA slot blot
hybridization gave comparable results. Furthermore, a combination of
the two methods allowed us to calculate specific cellular rRNA contents with respect to localization in the sediment profile. The rRNA contents
of Desulfosarcina-Desulfococcus cells were
highest in the first 5 mm of the sediment (0.9 and 1.4 fg,
respectively) and decreased steeply with depth, indicating that maximal
metabolic activity occurred close to the surface. Based on SRB cell
numbers, cellular sulfate reduction rates were calculated. The rates
were highest in the surface layer (0.14 fmol cell
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Community Structure, Cellular rRNA Content, and
Activity of Sulfate-Reducing Bacteria in Marine Arctic
Sediments
1
day
1), decreased by a factor of 3 within the first 2 cm,
and were relatively constant in deeper layers.
*
Corresponding author. Present address: TU
Hamburg-Harburg, Technical Microbiology, Denickestr. 15, 21071 Hamburg,
Germany. Phone: 49-40-428783964. Fax: 49-40-428782909. E-mail:
sahm{at}tu-harburg.de.
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