UW-Madison Dept of Bacteriology

Research Description

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 gamma-proteobacterium, 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, examining the interaction from both the bacterium and host sides.

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.