Hemalatha Saidasan et al. (2008) C.elegans Aging, Stress, Pathogenesis, and Heterochrony Meeting "Mode of Action of Microbial Toxins in C. elegans"

Michael Lawton, Hemalatha Saidasan

[C.elegans Aging, Stress, Pathogenesis, and Heterochrony Meeting, 2008]

Cereal crops, animal feed and processed grains throughout the world are frequently contaminated with mycotoxins such as deoxynivalenol (DON, or vomitoxin), 15-acetyl DON and nivalenol, which are produced by the plant pathogen Fusarium graminearum. For this reason, wheat and barley crops are routinely screened for the presence of these toxins. A solution to the problem of mycotoxin contamination of crop plants is a major goal of the US Department of Agriculture. Human and animal contamination with toxins occurs mainly through oral ingestion and pathogens and toxins must first traverse the intestinal epithelial barrier before inducing potential health effects. To identify cellular mechanisms involved in toxin uptake and pathogen entry into cells we studied the response of C. elegans mutants defective in intracellular trafficking. These studies revealed a critical role for this pathway in conditioning toxin sensitivity and pathogen susceptibility and suggest that pathogens may deliver toxins to host cells by exploiting existing pathways for uptake of molecules from the intestine. In addition to identifying mechanisms of pathogenesis and toxin action, these studies also form the basis for developing assays for small molecules that inhibit or counteract the effects of toxins and their corresponding pathogenic source.

Michael Lawton et al. (2008) C.elegans Aging, Stress, Pathogenesis, and Heterochrony Meeting "Genetic Dissection of Pathogenic Interactions of Lysobacter enzymogenes with C. elegans"

Michael Lawton, Hemalatha Saidasan

[C.elegans Aging, Stress, Pathogenesis, and Heterochrony Meeting, 2008]

Lysobacter enzymogenes infects lower plants, fungi and nematodes but not higher plants or mammals. L. enzymogenes produces copious amounts of lytic enzymes including chitinases, beta-1, 3-glucanases, and proteases while the recently sequenced genome of L. enzymogenes has revealed the presence of a type III secretion system (T3SS). We investigated the contributions of lytic enzymes and the T3SS to disease by feeding C. elegans with wild-type and mutant strains of L. enzymogenes. Wild-Type L. enzymogenes induced cuticle shrinkage, nuclear fragmentation, autophagy and cell death in C. elegans. Worms inoculated with either the clp- mutant (defective in lytic enzymes) or the deltaT3SS strain displayed a reduced mortality compared to wild type L. enzymogenes. Unlike infection with the wild-type strain or the clp- mutant, worms infected with the deltaT3SS strain did not develop autophagic vacuoles (although they still displayed cuticular shrinkage). Worms inoculated with the clp-/deltaT3SS double mutant displayed no abnormal effects, grew to maturity and gave rise to viable offspring. These results indicate that both the Clp-dependent pathway and the T3SS pathway contribute to virulence of L. enzymogenes on C. elegans. We are currently conducting a screen to identify the nature and targets of T3SS effectors. To identify the mechanism of cell death induced by L. enzymogenes, we studied the response of C. elegans mutants that are defective in different host programmed cell death pathways. These studies, coupled with pharmacological approaches indicate that susceptibility to L. enzymogenes in C. elegans is independent of the type I PCD pathway and the necrotic cell death pathway, but is dependant on the autophagic cell death pathway that is itself the target for T3SS effectors. Our data indicate that the engulfment pathway may also contribute to the expression of cell death in response to L. enzymogenes. We are currently using additional C. elegans mutants to investigate the contributions of other cell death pathways to host susceptibility. These results provide support for the development of C. elegans as a new multicellular model for molecular genetic dissection of the mechanisms of L. enzymogenes induced cell death. These studies will lay the foundation for identification of targets and inhibitors that can prevent L. enzymogenes induced cell death. This approach should also throw light on the genetic and molecular basis for broad host range specificity of L. enzymogenes.