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Applied and Environmental Microbiology, October 1998, p. 3633-3640, Vol. 64, No. 10
Section of Microbiology, Division of
Biological Sciences, College of Agriculture and Life Sciences,
Cornell University, Ithaca, New York 14853-8101
Received 27 April 1998/Accepted 28 July 1998
The presence of a highly conserved nahAc allele among
phylogenetically diverse bacteria carrying naphthalene-catabolic
plasmids provided evidence for in situ horizontal gene transfer at a
coal tar-contaminated site (J. B. Herrick, K. G. Stuart-Keil,
W. C. Ghiorse, and E. L. Madsen, Appl. Environ. Microbiol.
63:2330-2337, 1997). The objective of the present study was to
identify and characterize the different-sized naphthalene-catabolic
plasmids in order to determine the probable mechanism of horizontal
transfer of the nahAc gene in situ. Filter matings between
naphthalene-degrading bacterial isolates and their cured progeny
revealed that the naphthalene-catabolic plasmids were
self-transmissible. Limited interstrain transfer was also found.
Analysis of the restriction fragment length polymorphism (RFLP)
patterns indicated that catabolic plasmids from 12 site-derived isolates were closely related to each other and to the
naphthalene-catabolic plasmid (pDTG1) of Pseudomonas putida
NCIB 9816-4, which was isolated decades ago in Bangor, Wales. The
similarity among all site-derived naphthalene-catabolic plasmids and
pDTG1 was confirmed by using the entire pDTG1 plasmid as a probe in
Southern hybridizations. Two distinct but similar naphthalene-catabolic
plasmids were retrieved directly from the microbial community
indigenous to the contaminated site in a filter mating by using a
cured, rifampin-resistant site-derived isolate as the recipient. RFLP
patterns and Southern hybridization showed that both of these newly
retrieved plasmids, like the isolate-derived plasmids, were closely
related to pDTG1. These data indicate that a pDTG1-like plasmid is the
mobile genetic element responsible for transferring
naphthalene-catabolic genes among bacteria in situ. The pervasiveness
and persistence of this naphthalene-catabolic plasmid suggest that it
may have played a role in the adaptation of this microbial community to
the coal tar contamination at our study site.
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Plasmids Responsible for Horizontal Transfer of
Naphthalene Catabolism Genes between Bacteria at a Coal
Tar-Contaminated Site Are Homologous to pDTG1 from
Pseudomonas putida NCIB 9816-4

and
*
Corresponding author. Mailing address: Section of
Microbiology, Division of Biological Sciences, College of Agriculture
and Life Sciences, Cornell University, Ithaca, NY 14853-8101. Phone: (607) 255-3086. Fax: (607) 255-3904. E-mail: elm3{at}cornell.edu.
Present address: Department of Soil, Water, and Environmental
Science, University of Arizona, Tucson, AZ 85721.
Department of Biology, James Madison University, Harrisonburg, VA
22807.
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