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.

Click for video of Heterorhabditis bacteriophora infective juvenile nematodes regurgitating GFP-labeled Photorhabdus luminescens in insect hemolymph.
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).