Contact:
Department of Biological Sciences
University of Delaware
Newark, DE 19716
PH: (302) 831-8439
FAX: (302)831-2281
Email: herson@udel.edu
Education:
B.S., Cornell University
Ph.D., Rutgers University
Research Interests:
In our laboratory we are studying the physiology of organisms in water
and soil. We are particularly interested in the detection of these organisms
and their ability to survive in these environments. Our previous studies
with coliform organisms in drinking water have demonstrated the protective
role of attachment when these organisms are exposed to chlorine. They respond
to chlorine by synthesizing a subset of new proteins, one of which is in
the outer membrane. Our studies using INT, a tetrazolium dye, have indicated
that INT reduction is a more sensitive assay than plate counts in detecting
chlorine-injured organisms.
Helicobacter pylori, the causative agent of ulcers, is
considered an emerging pathogen. We are interested in determining
if this organism is spread by ground and surface waters.
and in the relative efficacy of ozone disinfection on H.
pylori and coliforms.
We have also shown that genetic transfer can occur in the low-nutrient, low temperature environment found in drinking water. Using a recombinant coliform harboring a non-transmissible plasmid, we demonstrated plasmid mobilization resulting from a tri-parental mating. Our studies with Pseudomonas stutzeri have demonstrated that DNA from this organism can persist and function as transforming DNA in a variety of waters.
Our current projects with organisms in soil involve bioremediation, a technology that uses microbes to degrade toxic chemicals. In this process an attempt is made to enhance microbial growth by initially assessing the biotic and abiotic factors at a site and then appropriately modifying them to optimize growth conditions. Although numerous remediation projects have been successfully carried out with a large variety of chemicals, the mechanisms which enable the microorganisms responsible for the degradation to survive and grow in the presence of the toxic chemical are not well understood. We have carried out studies using Pseudomonas putida (pWWO), an organism which can use toluene as a carbon and energy source. Using 2-D polyacrylamide gel electrophoresis we studied the physiological response of this organism when it was exposed to low, intermediate and high concentrations of toluene.
Current Research Projects:
The physiological response of Helicobacter pylori to ozone.
We are interested in the effect of ozone on Helicobacter pylori. These studies will be carried out by ozonating the cells in the presence of 35S methionine. Amino acid uptake will be measured to determine effect of ozone on transport. Changes in the protein profile will be monitored using two dimensional PAGE. We are also interested in determining the cellular site of the proteins that are produced in response to ozonation.
The detection of Helicobacter pylori in ground and surface waters.
We are using fluorescent-antibody INT (FAINT) and PCR to determine if viable Helicobacter pylori is present in a variety of surface and ground waters. We will also attempt to determine the effect of ozonation on the ability to detect H. pylori. Finding viable organisms would provide additional proof water can be a route of transmission for this pathogen.
The effect of MTBE on the ability of Pseudomonas putida mt-2 (pWWO) to degrade toluene.
In recent years MTBE has been added to gasoline as an oxygenate. Although this practice is now being questioned and there are concerns about its use, there are currently numerous sites contaminated with this chemical. Pseudomonas putida mt-2 (pWWO) is able to degrade toluene, one of the components of gasoline. It is an example of an organism that can be used to carry out bioremediation. The goal of this study is to determine the effect of MTBE on P. putida. We are specifically interested in determining if P. putida can use MTBE as a carbon and energy source and if the presence of MTBE affects the ability of P. putida to grow on toluene.
Teaching:
B648 - Bioremediation
B371 - Introduction to Microbiology
B171 - Microbiology in Modern Society
Publications:
Vercellone-Smith, P.A. and D.S. Herson. 1997. Toluene elicits a carbon starvation response in Pseudomonas putida mt-2 containing TOL-plasmid pWWO. Appl. Environ. Microbiol. 63:1925-1932.
Berlin, D., D. S. Herson, D. T. Hicks, and D. G. Hoover. 1999. Response of pathogenic species of Vibrio to high hydrostatic pressure. Appl. Environ. Microbiol. 65:2776-2780.
Baker, K.H. and d.S. Herson. 1999. Detection and occurrence of indicator
organisms and pathogens. Manuscript accepted. Water environment
Research.