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Appl. Environ. Microbiol., 11 1997, 4237-4242, Vol 63, No. 11
JM Gonzalez and MA Moran
A cluster of marine bacteria within the alpha-3 subclass of the class
Proteobacteria accounted for up to 28% of the 16S ribosomal DNA (rDNA)
sequences in seawater samples from the coast of the southeastern United
States. Two independent oligonucleotide probes targeting 16S rDNA of this
"marine alpha" cluster indicate that the group dominates bacterioplankton
communities in estuarine and nearshore regions of the southeastern U.S.
coast. Marine alpha bacteria decline predictably in abundance with
decreasing salinity along estuarine transsects and are not detectable in
low-salinity (5%) or freshwater samples. Sequences of 16S rDNA obtained
from seawater by PCR with one group-specific oligonucleotide as a primer
confirm that the oligonucleotide targets only members of this phylogenetic
cluster. Likewise, sequences of 16S rDNA obtained from seawater by PCR with
several different pairs of nonspecific primers show an unusually high
abundance of marine alpha sequences (52 to 84%) among the clones, which
possibly indicates a PCR bias toward the group. Members of the marine alpha
group were readily cultured from coastal seawater, accounting for 40% of
the colonies isolated on low-nutrient marine agar, based on hybridizations
with the group-specific 16S rDNA probe and on sequence analysis. This is
the first description of a numerically dominant cluster of coastal
bacteria, identified by molecular techniques, that can be readily cultured
and studied in the laboratory.
Copyright © 1997, American Society for Microbiology
Numerical dominance of a group of marine bacteria in the alpha-subclass of the class Proteobacteria in coastal seawater
Department of Marine Sciences, University of Georgia, Athens 30602, USA. gonzalez@uga.cc.uga.edu
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