Faculty
Jo Handelsman
(608) 263-8783
Department of Plant Pathology
University of Wisconsin - Madison
1630 Linden Dr.
Madison, WI 53706
rev. January 15, 2004
[MORE-3]
Molecular Ecology
of the Insect Midgut Microbiota
The third
area of research in the Handelsman lab is the gypsy moth midgut, which
serves as a model for studying a contained community, with the goal of
attaining a comprehensive understanding of its function at the genomic,
chemical, and ecological levels. We
initially started studying the gypsy moth community after we and our collaborators
demonstrated that zwittermicin A, the antibiotic produced by B. cereus
strains that are active in biocontrol, is a powerful potentiator of
Bacillus thuringiensis toxicity to gypsy moth larvae. This finding led us to study the molecular ecology
of the microbiota of the insect midgut because one mechanism by which
zwittermicin A might potentiate is by altering the composition of the
midgut community. To test this
hypothesis, we studied the community by culture-dependent and culture-independent
methods. We found that the gypsy
moth midgut contains a rich and diverse community; that culture-independent
methods reveal a greater diversity of bacteria than culturing; and that
zwittermicin A and foliage species in the diet alter the composition of
the community. Perhaps the most intriguing finding is that
all gypsy moths examined, independent of the source of the larvae or their
diet, contained a culturable Enterococcus faecalis and a 16S rRNA
sequence of a g-Proteobacterium
that deeply diverged from all known sequences in this Division of bacteria.
We are
keen to study the interaction between the readily culturable E. faecalis
and the as yet unculturable g-Proteobacterium. But there are few methods
in microbial ecology that facilitate the isolation of single microbial
variables in an otherwise undisturbed ecosystem. Therefore, our initial studies will involve
developing methods to subtract certain species from the midgut community
opening up the possibility of defining the function of each member of
the community. To accomplish this,
in collaboration with entomologist Ken Raffa (http://plantpath.wisc.edu/~raffa/)
and experts in bacterial plasmids and gene expression (http://www.bact.wisc.edu/GradStudies/FilutowiczMarcin.html),
we have begun building microbial assassins, which we call “The Trojan
Horse,” that will enter a community and selectively destroy certain members. The initial application of this technology will
be to test the hypothesis that E. faecalis provides the gypsy moth
with developmental signals or nutrients, or reduces its vulnerability
to invading pathogens or parasites.
The gypsy
moth system presents the opportunity to conduct a comprehensive analysis
of a metagenome since there are only about a dozen species in the gut
of the caterpillar. It is feasible,
with today’s technology, to fully sequence the genomes of these organisms
and reassemble them. Moreover,
the community is sufficiently simple and defined, that it is possible
to assign functions to most of the organisms.