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Applied and Environmental Microbiology, September 2001, p. 3897-3903, Vol. 67, No. 9
Department of Civil and Environmental
Engineering1 and Center for
Environmental Health Sciences,2
Massachusetts Institute of Technology, Cambridge, Massachusetts
02139
Received 5 February 2001/Accepted 21 June 2001
A novel quantitative PCR (QPCR) approach, which combines
competitive PCR with constant-denaturant capillary electrophoresis (CDCE), was adapted for enumerating microbial cells in environmental samples using the marine nanoflagellate Cafeteria
roenbergensis as a model organism. Competitive PCR has been used
successfully for quantification of DNA in environmental samples.
However, this technique is labor intensive, and its accuracy is
dependent on an internal competitor, which must possess the same
amplification efficiency as the target yet can be easily discriminated
from the target DNA. The use of CDCE circumvented these problems, as its high resolution permitted the use of an internal competitor which
differed from the target DNA fragment by a single base and thus ensured
that both sequences could be amplified with equal efficiency. The
sensitivity of CDCE also enabled specific and precise detection of
sequences over a broad range of concentrations. The combined
competitive QPCR and CDCE approach accurately enumerated C. roenbergensis cells in eutrophic, coastal seawater at abundances ranging from approximately 10 to 104 cells
ml
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.9.3897-3903.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Combination of Competitive Quantitative PCR and
Constant-Denaturant Capillary Electrophoresis for High-Resolution
Detection and Enumeration of Microbial Cells

1. The QPCR cell estimates were confirmed by
fluorescent in situ hybridization counts, but estimates of samples with
<50 cells ml
1 by QPCR were less variable. This novel
approach extends the usefulness of competitive QPCR by demonstrating
its ability to reliably enumerate microorganisms at a range of
environmentally relevant cell concentrations in complex aquatic samples.
*
Corresponding author. Mailing address: Ralph M. Parsons
Laboratory, 48-421, Massachusetts Institute of Technology, Cambridge, MA 02139. Phone: (617) 253-7128. Fax: (617) 258-8850. E-mail: mpolz{at}mit.edu.
Present address: Biology Department, Temple University,
Philadelphia, PA 19122.
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