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Applied and Environmental Microbiology, November 2001, p. 5240-5246, Vol. 67, No. 11
Department of Biological
Sciences,1 Key Centre for Biodiversity
and Bioresources,2 and Department of
Chemistry,3 Macquarie University, Sydney,
New South Wales 2109, Australia
Received 24 May 2001/Accepted 20 August 2001
The vast majority of bacteria in the environment have yet to be
cultured. Consequently, a major proportion of both genetic diversity
within known gene families and an unknown number of novel gene families
reside in these uncultured organisms. Isolation of these genes is
limited by lack of sequence information. Where such sequence data
exist, PCR directed at conserved sequence motifs recovers only partial
genes. Here we outline a strategy for recovering complete open reading
frames from environmental DNA samples. PCR assays were designed to
target the 59-base element family of recombination sites that flank
gene cassettes associated with integrons. Using such assays, diverse
gene cassettes could be amplified from the vast majority of
environmental DNA samples tested. These gene cassettes contained
complete open reading frames, the majority of which were associated
with ribosome binding sites. Novel genes with clear homologies to
phosphotransferase, DNA glycosylase, methyl transferase, and
thiotransferase genes were identified. However, the majority of
amplified gene cassettes contained open reading frames with no
identifiable homologues in databases. Accumulation analysis of the gene
cassettes amplified from soil samples showed no signs of saturation,
and soil samples taken at 1-m intervals along transects demonstrated
different amplification profiles. Taken together, the genetic novelty,
steep accumulation curves, and spatial heterogeneity of genes recovered
show that this method taps into a vast pool of unexploited genetic
diversity. The success of this approach indicates that mobile gene
cassettes and, by inference, integrons are widespread in natural
environments and are likely to contribute significantly to bacterial diversity.
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.11.5240-5246.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Gene Cassette PCR: Sequence-Independent Recovery of
Entire Genes from Environmental DNA
*
Corresponding author. Mailing address: Department of
Biological Sciences, Macquarie University, Sydney, NSW 2109, Australia. Phone: (612) 9850 8164. Fax: (612) 9850 8245. E-mail:
hstokes{at}rna.bio.mq.edu.au.
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