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Appl. Environ. Microbiol., Feb 1996, 625-630, Vol 62, No. 2
MT Suzuki and SJ Giovannoni
The PCR is used widely for the study of rRNA genes amplified from mixed
microbial populations. These studies resemble quantitative applications of
PCR in that the templates are mixtures of homologs and the relative
abundance of amplicons is thought to provide some measure of the gene
ratios in the starting mixture. Although such studies have established the
presence of novel rRNA genes in many natural ecosystems, inferences about
gene abundance have been limited by uncertainties about the relative
efficiency of gene amplification in the PCR. To address this question,
three rRNA gene standards were prepared by PCR, mixed in known proportions,
and amplified a second time by using primer pairs in which one primer was
labeled with a fluorescent nucleotide derivative. The PCR products were
digested with restriction endonucleases, and the frequencies of genes in
the products were determined by electrophoresis on an Applied Biosystems
373A automated DNA sequencer in Genescan mode. Mixtures of two templates
amplified with the 519F-1406R primer pair yielded products in the predicted
proportions. A second primer pair (27F-338R) resulted in strong bias
towards 1:1 mixtures of genes in final products, regardless of the initial
proportions of the templates. This bias was strongly dependent on the
number of cycles of replication. The results fit a kinetic model in which
the reannealing of genes progressively inhibits the formation of
template-primer hybrids.
Copyright © 1996, American Society for Microbiology
Bias caused by template annealing in the amplification of mixtures of 16S rRNA genes by PCR
College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis 97331, USA.
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