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Appl. Environ. Microbiol., 04 1996, 1171-1177, Vol 62, No. 4
DA Gordon and SJ Giovannoni
A gene lineage (SAR406) related to Chlorobium and Fibrobacter species was
found in 16S rRNA gene clone libraries prepared from samples from two
oceans. The clone libraries were constructed from total picoplankton
genomic DNA to assess bacterial diversity in the lower surface layer. The
samples were collected by filtration from a depth of 80 m at a site in the
western Sargasso Sea and from a depth of 120 m at a site in the Pacific
Ocean, approximately 70 km from the Oregon coast. The PCR and primers which
amplified nearly full-length 16S rRNA genes were used to prepare the clone
libraries. Among the diverse gene clones in these libraries were two
related clones (SAR406 and OCS307) which could not be assigned to any of
the major bacterial phyla. Phylogenetic analyses demonstrated that these
genes were distant relatives of the genus Fibrobacter and the green sulfur
bacterial phylum, which includes the genus Chlorobium. The inclusion of
SAR406 in phylogenetic trees inferred by several methods resulted in
support from bootstrap replicates for the conclusion that Fibrobacter and
Chlorobium species and SAR406 are a monophyletic group. An oligonucleotide
probe that selectively hybridized to clone SAR406 was used to examine the
distribution of this gene lineage in vertical profiles from the Atlantic
and Pacific Oceans and in monthly time series at 0 and 200 m in the
Atlantic Ocean. During stratified periods, the genes were most abundant
slightly below the deep chlorophyll layer. Seasonal changes in the surface
abundance of SAR406 rDNA were highly correlated with chlorophyll a levels
(r = 0.75).
Copyright © 1996, American Society for Microbiology
Detection of stratified microbial populations related to Chlorobium and Fibrobacter species in the Atlantic and Pacific oceans
Department of Microbiology, Oregon State University, Corvallis 97331, USA.
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