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Courses:
Allied Health Microbiology
(BIO 280), Microbial Ecology (BIO 453/553)
Research
Interests: Environmental and Molecular Microbiology
In our laboratory, we use molecular, genetic, and
microbiological
techniques to study the lateral transfer of genes to and among bacteria
native to area streams, stream sediments, and soils. Lateral gene
transfer - as opposed to the 'vertical' transfer of genes via simple
cell division - allows genes to move between mature cells and thus to
potentially spread very quickly through a population and even from
species to species. Lateral gene transfer has had a profound effect on
genome evolution, on pollutant biodegradation, and particularly on the
development of antibiotic resistance in bacteria. Our current focus is
on the transfer of resistance genes in streams and sediments.
Antibiotic overuse and misuse may lead to selection for resistance
genes, many of which are found on mobile genetic elements such as
plasmids and transposons, and these can potentially be transferred from
human or animal strains to bacteria in the environment. Resistant
environmental bacterial populations may then act as environmental
reservoirs and evolutionary "incubators" of resistance genes, thus
providing new variants and combinations of resistance phenotypes for
subsequent transfer to human and animal pathogenic bacteria. We are
currently using genetic 'capture' techniques to study actively
transferring tetracycline resistance plasmids which, though acquired
from native stream bacteria, may have their origins in introduced,
antibiotic-selected fecal bacteria. We are also studying the
distribution, occurrence, and gene content of integrons - DNA regions
that collect multiple resistance genes - in fecal and environmental
bacteria.
Selected
Publications:
Wilson, M.S., J. B. Herrick, C. O. Jeon, D. E.
Hinman, and E.
L. Madsen. 2003. Horizontal transfer of phn-Ac dioxygenase genes within
one of two phenotypically and genotypically distinctive
naphthalene-degrading guilds from adjacent soil environments. Appl.
Environ. Microbiol. 69: 2172-2181.
Stuart-Keil, K.G., A. M. Hohnstock, K. P. Drees,
J. B. Herrick,
and E. L. Madsen. 1998. 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. Appl. Environ. Microbiol. 64: 3633-3640.
Herrick, J. B., E. L. Madsen, and W. C. Ghiorse.
1997. Natural
horizontal transfer of a naphthalene dioxygenase gene between bacteria
native to a coal tar-contaminated field site. Appl. Environ. Microbiol.
63: 2330-2337.
Herrick, J. B., D. N. Miller, E. L. Madsen, and W.
C. Ghiorse.
1996. Extraction, purification, and PCR amplification of microbial DNA
from sediments and soils. In PCR: Essential Techniques, Julian F. Burke
(ed.). Bios Sci. Publ., Oxford.
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