Research
- Genetic
analysis of symbiosis in the insect pathogen Photorhabdus
luminescens (Enterobacteriaceae) and the nematode
host, Heterorhabditis bacteriophora.
- Analysis
of insect induced regurgitation behavior of H.
bacteriophora nematodes.
- Microbial
interactions of the squid accessory nidamental gland/egg
case symbiosis.
Essentially
every organism is associated with symbiotic or beneficial
bacteria during some or all of its life. These bacteria
can have important or even essential functions to their
hosts. The analysis of animal and plant symbioses has
revealed several important pathways involved in symbiosis
related to pathogenesis and innate immunity. Given similar
pathways are involved in symbiosis and pathogenesis,
how then are symbiotic bacteria distinguished from non-symbiotic
or pathogenic bacteria? I am using the obligate mutualism
between insect parasitic nematodes and bacteria to learn
how symbiotic or beneficial bacteria are selected and
maintained in an animal intestine.
The
bacterium, Photorhabdus luminescens, is an
enteric related to many medically relevant pathogens
(e.g. Yersinia pestis ) and is an ideal model
to study symbiosis because: 1) its genome is completely
sequenced 2) it is amenable to genetic analysis 3) it
specifically colonizes the intestine of the infective
juvenile stage of the nematode, Heterorhabditis
bacteriophora, 4) required for nematode growth
and reproduction and 5) it is a virulent pathogen when
injected into insects.
The
nematode Heterorhabditis bacteriophora is an
ideal animal model for the study of symbiosis because
1) it phylogenetically related to and shares many attributes
with Caenorhabditis elegans (e.g.small size,
short generation time, high fecundity), 2) forward and
reverse genetic techniques have been successful, 3)
it specifically transmits P. luminescens bacteria
in the infective juvenile stage intestine and requires
the bacteria for insect pathogenicity and for growth
and reproduction 4) can be propagated on agar based
medium containing symbiont P. luminescens and
is easily made axenic, and 4) regurgitates symbiotic
bacteria in insect hemolymph.
Genetic
and molecular approaches are being taken in both the
symbiont and nematode host to elucidate how symbiotic
host-bacterial interactions are established and maintained
while pathogenic interactions are suppressed. Understanding
symbiosis in this model system will contribute to our
understanding of symbiotic or beneficial interactions
that occur every day in most organisms (e.g. the human
gastrointestinal tract). |
