Associate Professor of Biology
B.S. - Brigham Young University
Courses: Allied Health Microbiology (BIO 280), Microbial Ecology (BIO 453/553)
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.
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.