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rather small. The other cluster of sequences observed by Giovanonni and colleagues (dubbed
Sar 11 cluster) grouped most closely with the alpha subdivision of Proteobacteria, a
subdivision which contains both phototrophic and oligotrophic genera. However, no known,
cultivated organisms are very closely affiliated with this cluster. To assess the relative
abundance of the Sar 11 group, Giovanonni et al., used the newly acquired sequence data to
design an oligonucleotide hybridization probe which specifically recognizes the Sar 11 group.
Hybridization of this group-specific probe to mixed population nucleic acids indicated that Sar
11 cluster rRNA comprised ca. 15 % of the total eubacterial rRNA in the original sample.
Based on these data, the authors suggest that this novel group of organisms likely plays an
important ecological role in the Sargasso Sea. This hypothesis has been recently extended by
data obtained in the Central North Pacific Ocean, as described below.
A slightly different approach was used to analyze small subunit rRNA genes from oligotrophic
bacterioplankton populations of the Central North Pacific (DeLong et al., 1989b; Schmidt et
al., submitted). Bacterioplankton samples were collected at a Hawaii Global Ocean Flux Study
site (Station Aloha, Drs. David Karl and Chris Winn, project coordinators), located
approximately 100 km north of Oahu. High molecular weight DNA was extracted from the
concentrated bacterioplankton, and used to construct a clone library in bacteriophage lambda.
A total of ca. 1 x 10 7 recombinant bacteriophage clones were recovered. About 3 x 104 of
these were screened for rRNA genes, resulting in the isolation of 40 rRNA gene-containing
recombinant clones. Partial small subunit rRNA sequencing revealed the phylogenetic
affiliations of specific population members. The diversity of small subunit rRNA genes
recovered spanned a fairly broad phylogenetic range: clones representative of the
cyanobacteria, the alpha, and the gamma subdivision of the Proteobacteria, as well as
eukaryotic dinoflagellates, were all present in the library.
Preliminary comparisons of partial small subunit rRNA sequence data (ca. 190 nucleotides)
from Central North Pacific bacterioplankton (Schmidt et al., submitted), with those obtained
by Giovanonni et al., in the Sargasso Sea (1990a), reveals striking similarities (Figure 1).
Cloned cyanobacterial sequences obtained from two different ocean gyres displayed similarity
values ranging from 0.955 to 0.985. The cyanobacterial sequences form distinct clusters,
represented in both the Sargasso Sea and the Central North Pacific (Figure. la). These groups
rather small. The other cluster of sequences observed by Giovanonni and colleagues (dubbed
Sar 11 cluster) grouped most closely with the alpha subdivision of Proteobacteria, a
subdivision which contains both phototrophic and oligotrophic genera. However, no known,
cultivated organisms are very closely affiliated with this cluster. To assess the relative
abundance of the Sar 11 group, Giovanonni et al., used the newly acquired sequence data to
design an oligonucleotide hybridization probe which specifically recognizes the Sar 11 group.
Hybridization of this group-specific probe to mixed population nucleic acids indicated that Sar
11 cluster rRNA comprised ca. 15 % of the total eubacterial rRNA in the original sample.
Based on these data, the authors suggest that this novel group of organisms likely plays an
important ecological role in the Sargasso Sea. This hypothesis has been recently extended by
data obtained in the Central North Pacific Ocean, as described below.
A slightly different approach was used to analyze small subunit rRNA genes from oligotrophic
bacterioplankton populations of the Central North Pacific (DeLong et al., 1989b; Schmidt et
al., submitted). Bacterioplankton samples were collected at a Hawaii Global Ocean Flux Study
site (Station Aloha, Drs. David Karl and Chris Winn, project coordinators), located
approximately 100 km north of Oahu. High molecular weight DNA was extracted from the
concentrated bacterioplankton, and used to construct a clone library in bacteriophage lambda.
A total of ca. 1 x 10 7 recombinant bacteriophage clones were recovered. About 3 x 104 of
these were screened for rRNA genes, resulting in the isolation of 40 rRNA gene-containing
recombinant clones. Partial small subunit rRNA sequencing revealed the phylogenetic
affiliations of specific population members. The diversity of small subunit rRNA genes
recovered spanned a fairly broad phylogenetic range: clones representative of the
cyanobacteria, the alpha, and the gamma subdivision of the Proteobacteria, as well as
eukaryotic dinoflagellates, were all present in the library.
Preliminary comparisons of partial small subunit rRNA sequence data (ca. 190 nucleotides)
from Central North Pacific bacterioplankton (Schmidt et al., submitted), with those obtained
by Giovanonni et al., in the Sargasso Sea (1990a), reveals striking similarities (Figure 1).
Cloned cyanobacterial sequences obtained from two different ocean gyres displayed similarity
values ranging from 0.955 to 0.985. The cyanobacterial sequences form distinct clusters,
represented in both the Sargasso Sea and the Central North Pacific (Figure. la). These groups