Pore worms: using Caenorhabditis elegans to study how bacterial toxins interact with their target host.

The interaction of pathogenic bacteria with a target host is regulated both by bacterial virulence factors and by host components that either protect the host or that promote pathogenesis. The soil nematode Caenorhabditis elegans is a host for a number of bacterial pathogens, as briefly reviewed here. Bacillus thuringiensis (Bt) is a pathogenic bacteria that C. elegans is likely to encounter naturally in the soil. The pore-forming Crystal (Cry) toxins made by Bt are recognized as the dominant virulence factor in this host-pathogen interaction. Forward genetic screens for C. elegans mutants resistant to the Cry toxin, Cry5B, have identified a host carbohydrate structure that promotes pathogenesis. Data suggest this structure is likely to be a Cry5B receptor expressed in the host intestine. This finding is discussed in light of other carbohydrate receptors for bacterial toxins. To investigate host-toxin interactions on a global level, the response of C. elegans to the pore-forming Cry5B is also being investigated by gene transcription profiling (microarrays). These data are beginning to reveal a diverse intracellular response to toxin exposure. To put these investigations in perspective, host responses to other pore-forming toxins are discussed. Investigations with Cry5B in C. elegans show a promising beginning in helping to elucidate host-toxin and host-pathogen interactions.