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Applied and Environmental Microbiology, April 2001, p. 1663-1674, Vol. 67, No. 4
Marine Sciences Research Center, State
University of New York at Stony Brook, Stony Brook, New York
11794-5000
Received 11 September 2000/Accepted 24 January 2001
Microbial community samples were collected from the anoxic zone of
the Cariaco Basin at depths of 320, 500, and 1,310 m on a November 1996 cruise and were used to construct 16S ribosomal DNA libraries. Of
60 nonchimeric sequences in the 320-m library, 56 belonged to
the
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.4.1663-1674.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Phylogenetic Diversity of Bacterial and Archaeal
Communities in the Anoxic Zone of the Cariaco Basin

subdivision of the Proteobacteria
(
-Proteobacteria) and 53 were closely related to
ectosymbionts of Rimicaris exoculata and Alvinella
pompejana, which are referred to here as epsilon symbiont
relatives (ESR). The 500-m library contained sequences affiliated with
the fibrobacteria, the Flexibacter-Cytophaga-Bacteroides division, the division Verrucomicrobia, the division
Proteobacteria, and the OP3 candidate division. The
Proteobacteria included members of the
,
,
and new candidate
subdivisions, and
-proteobacterial sequences were dominant (25.6%)
among the proteobacterial sequences. As in the 320-m library, the
majority of the
-proteobacteria belonged to the ESR group. The genus
Fibrobacter and its relatives were the second largest group
in the library (23.6%), followed by the
-proteobacteria and the
-proteobacteria. The 1,310-m library had the greatest diversity; 59 nonchimeric clones in the library contained 30 unique sequences
belonging to the planctomycetes, the fibrobacteria, the
Flexibacter-Cytophaga-Bacteroides division, the
Proteobacteria, and the OP3 and OP8 candidate divisions.
The proteobacteria included members of new candidate subdivisions and
the
,
,
, and
-subdivisions. ESR sequences were still present in the 1,310-m library but in a much lower proportion (8.5%).
One archaeal sequence was present in the 500-m library (2% of all
microorganisms in the library), and eight archaeal sequences were
present in the 1,310-m library (13.6%). All archaeal sequences fell
into two groups; two clones in the 1,310-m library belonged to the
kingdom Crenarchaeota and the remaining sequences in both
libraries belonged to the kingdom Euryarchaeota. The latter group appears to be related to the Eel-TA1f2 sequence, which belongs to
an archaeon suggested to be able to oxidize methane anaerobically. Based on phylogenetic inferences and measurements of dark
CO2 fixation, we hypothesized that (i) the ESR are
autotrophic anaerobic sulfide oxidizers, (ii) sulfate reduction and
fermentative metabolism may be carried out by a large number of
bacteria in the 500- and 1,310-m libraries, and (iii) members of the
Euryarchaeota found in relatively large numbers in the
1,310-m library may be involved in anaerobic methane oxidation.
Overall, the composition of microbial communities from the Cariaco
Basin resembles the compositions of communities from several anaerobic
sediments, supporting the hypothesis that the Cariaco Basin water
column is similar to anaerobic sediments.
*
Corresponding author. Mailing address: Marine Sciences
Research Center, State University of New York at Stony Brook, Stony Brook, NY 11794-5000. Phone: (631) 632-9233. Fax: (631) 632-8820. E-mail: andrei{at}notes.cc.sunysb.edu.
Contribution no. 1184 from Marine Sciences Research Center, State
University of New York at Stony Brook.
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