The Aroian laboratory is interested in understanding
bacterial pathogenesis in animals. We are studying the nematode
Caenorhabditis elegans as a model for understanding what
host factors are required for pathogenesis and what host factors
are required to defend the animal from C. elegans fed certain Bt crystal
proteins rapidly become sick and develop intestinal pathologies
(Figure 1). To better understand how Cry proteins attack, we isolated
mutants resistant to Although C. elegans is a beneficial soil-dwelling nematode, some of nematodes are parasites. We have shown that some Cry proteins are toxic to a wide range of nematodes and are currently working to determine if these organic, human-safe proteins can be used to control harmful plant nematodes. We are also expanding our understanding of host-toxin interactions. To complement work on resistant mutants, we are characterizing mutants that have increased sensitivity to the pore-forming toxin attack. These hypersensitive mutants may encode host genes that normally act to defend the animal from the toxin. Thus, when a hyp gene is mutated, the toxin acts more quickly and more potently. Such genes may play a role in human defense against pore-forming toxins as well. We are also looking at host response to the toxin on a genomic scale. Within one hour, we have found that transcription of many genes is strongly turned off and on. We are currently working to understand what functional role these genes play in host-toxin interactions. Given the importance of public education, we are assembling a webpage to elucidate the benefits and risks of transgenic crops that express Bt crystal proteins. Cappello, M., Bungiro, R.D., Harrison, L.M., Bischof, L.J., Griffitts, J.S., Barrows, B.D., and Aroian, R.V. (2006). A purified Bacillus thuringiensis crystal protein with therapeutic activity against the hookworm parasite Ancylostoma ceylanicum. Proc. Natl. Acad. Sci. 103(41): 15154-15159.
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bacterial
attack. We are using helical pore-forming toxins (Crystal proteins)
made by the bacterium Bacillus thuringiensis (Bt) as the
means of pathogenic attack. Since helical pore-forming toxins
are a common weapon of pathogenic bacteria (e.g., Vibrio cholerae,
Shigella dysenteriae, Bordetulla pertussis, enterotoxigenic
E. coli), we view the interaction of Crystal proteins with
the nematode as a model for important aspects of bacterial pathogenesis.
Furthermore, Bt Crystal (Cry) proteins, which are non-toxic
to humans, are used worldwide in the control of insect pests that
eat crops (caterpillars) and that carry disease (mosquitoes and
black flies). A better understanding of Cry protein mechanism
of action and development of resistance may allow people to better
useof this natural resource.
attack
by Cry proteins. The genes, call the bre genes for Bt
toxin resistant, are required for Cry toxin to kill-when
these genes are mutated the nematodes that eat the toxin are no
longer killed. One of these genes, bre-5, has been cloned
and encodes a glycosyltransferase, an enzyme thatadds sugars (carbohydrates)
onto proteins or lipids. Our data suggest that bre-5 makes
a carbohydrate present at the surface of the gut that is required
for toxin to bind to the gut, subsequently leading to pathogenesis
(Figure 2). Thus, as other groups working in insects have shown,
binding to receptor is a key step in Cry toxin pathogenesis and
in the development of resistance. We are currently working to
identify in more detail the receptor that Cry protein binds to
and to characterize other modes of resistance to Cry proteins.
