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Appl. Environ. Microbiol., 03 1997, 1028-1033, Vol 63, No. 3
MF Polz and CM Cavanaugh
A simple method for the quantification of uncultured microorganisms in the
environment was developed. In vitro-transcribed 16S rRNA is used as a
template for midpoint dissociation temperature (Td) determinations of
specific oligonucleotide probes and as a standard in quantitative probing.
It replaces the need for total nucleic acids extracted from pure cultures
of the organisms to be quantified. A sense RNA of a size almost identical
to that of native 16S rRNA can be transcribed from ribosomal DNA clones
recovered in studies of the phylogenetic diversity of microbial
communities. This in vitro-transcribed rRNA yields dissociation curves
typical of oligonucleotides. They parallel curves determined with total
nucleic acids but yield slightly higher Td values. Neither unspecific
sticking of the probe nor probe washing off the DNA template at low
temperatures fully accounted for the discrepancy in probe release from the
two templates. This suggests that the native rRNA itself has melting
characteristics different from those of its in vitro-transcribed
counterpart. However, this difference does not affect the performance of in
vitro-transcribed rRNA compared with total nucleic acids as a standard in
quantitative hybridizations. No difference was found between the estimates
of the relative quantity of a single bacterial species in a mixed community
obtained with the two standards, regardless of whether DNA was removed from
the samples. This protocol will allow the large-scale quantification of the
ecological importance of uncultured microorganisms in natural environments
for the first time.
Copyright © 1997, American Society for Microbiology
A simple method for quantification of uncultured microorganisms in the environment based on in vitro transcription of 16S rRNA
Biological Laboratories, Harvard University, Cambridge, Massachusetts 02138, USA.
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