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Heidi Goodrich-Blair

Email: hgblair@bact.wisc.edu

Assistant Professor Degrees: Ph.D., 1993, University of Albany, SUNY Postdoctorial Research University at Albany, SUNY; Harvard Medical School

MUTUALISM AND PATHOGENESIS: MOLECULAR MECHANISMS OF NEMATODE/BACTERIUM/INSECT INTERACTIONS

Our research is aimed at understanding, at a molecular level, how microbes survive and flourish in the environments they occupy. Survival for many microbes is dependent upon their ability to interact with other organisms. To understand host-microbe interactions, our lab focuses on a gram-negative bacterium, Xenorhabdus nematophila. This bacterium is a symbiont of the insect-infecting nematode Steinernema carpocapsae and is responsible for killing the insect larvae that this pair infects.

X. nematophila resides as a symbiont within a specialized intestinal vesicle of the insect-infecting nematode. Each of these two organisms requires the other to grow and reproduce, a process that occurs within the insect. The bacterium, X. nematophila, is the actual insect pathogen; it produces exo- and endo-toxins that can rapidly kill an insect host. In addition, once inside an insect host, X. nematophila expresses degradative functions such as proteases and lipases that convert insect host tissues into products that can be utilized by the nematode. Thus, X. nematophila is essential for both insect host killing and nematode development.

X. nematophila is a model for both positive and negative host-microbe interactions, knowledge of which will improve our ability to combat and/or utilize microorganisms to our own benefit. Furthermore, X. nematophila is part of a tripartite system (insect, nematode, and bacterium) that has potential use as an alternative to insecticides. Understanding the relationship between the members of this system will greatly improve their use in biocontrol. In our work we use molecular, genetic, and biochemical techniques to ask basic biological questions involving the interaction of X. nematophila with its hosts.

Currently, there are several avenues of research in the lab. In one, we are examining how starvation contributes to both beneficial host associations (with the nematode) and pathogenicity (toward insects) in X. nematophila. In another, we are identifying bacterial genes and gene products necessary for colonization of nematode intestines. Third, we are determining which genes and gene products are necessary for virulence toward insects, as well as analyzing insect innate immune responses to X. nematophila infection. This last project is funded by a recently awarded five-year grant from the Burroughs Wellcome Foundation.

The results of our work will have an impact on our understanding of any system in which microbes interact with a eukaryotic host, including pathogenic and symbiotic associations. It will illustrate the mechanisms by which a single bacterium can form a beneficial association with one organism and a harmful interaction with another. In addition, our findings will have implications in the fields of biocontrol and microbial ecology and development.

References:

Vivas, E.I. and Goodrich-Blair, H. (2001) Xenorhabdus nematophilus as a model for host-bacterium interactions: rpoS is necessary for mutualism but not pathogenesis. J. Bacteriol. 183:4687-4693.

Heungens, K., Cowles, C.E., and Goodrich-Blair, H. (2002) Identification and characterization of Xenorhabdus nematophila genes required for mutualistic colonization of Steinernema carpocapsae nematodes. Molec. Microbiol. 45 :1337-1353.

Zhou, X., Kaya, H.K., Heungens, K., and Goodrich-Blair, H. (2002) Response of Ants to a Deterrent Factor(s) Produced by the Symbiotic Bacteria of Entomopathogenic Nematodes. Appl. Environ. Microbiol. 68:6202-6209.

Martens, E.C., Heungens, K., and Goodrich-Blair, H. (2003) Early colonization events in the mutualistic association between Steinernema carpocapsae nematodes and Xenorhabdus nematophila. J. Bacteriol. 185:3147-3154.

Martens, E.C., Vokal, D.L., Pelliteri, M.C., Menard, M.L., and Goodrich-Blair, H. (2003) Xenorhabdus nematophila requires an intact iscRSUA-hscBA-fdx operon to colonize Steinernema carpocapsae nematodes J. Bacteriol. 185:3678-3682.

Andersen, A.W., Heungens, K., Wassarman, K.M., and Goodrich-Blair, H. (2003) Evidence that Xenorhabdus nematophila Symbiosis Region 2 encodes a regulatory RNA, NilD, necessary for symbiosis with Steinernema carpocapsae nematodes. Submitted.

Relevant links

Entomopathogenic nematodes and bacteria:

http://www.bact.wisc.edu/epnb/

http://www2.oardc.ohio-state.edu/nematodes/

Animal-microbe associations:

http://www.sp.uconn.edu/~mcbstaff/graf/Sym.html

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