Graduate Research and Discovery Symposium (GRADS)


The Role of the bacterial secondary messenger, cyclic di-guanosine-monophosphate, in Interkingdom communication


Min Cao, Ph.D.

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Background: Cyclic di-nucleotides (CDNs) are described as important secondary signaling molecules in bacteria that have the ability to regulate a wide range of processes. More recently, the role of these molecules has expanded to the eukaryotic domain where they act in modulating the innate immune response, but their influences have the potential to be far reaching. Through our studies, we have shown that Caenorhabditis elegans are able to detect and are attracted towards numerous signaling molecules produced by Vibrio cholerae, specifically cyclic di-guanosine-monophosphate (c-di-GMP), even though this bacterium kills the host at a high rate. We investigate how c-di-GMP is able to communicate with a host, and its effect on innate immunity. Methods: Choice index assays were performed on C. elegans to observe choice preference of the host towards different concentrations of CDNs produced by V. cholerae. LC-MS was utilized to detect both intracellular and extracellular levels of CDNs produced by V. cholerae during growth. Choice index assays using C. elegans with mutations in neuronal genes allowed for analysis of pathways involved in c-di-GMP detection. Killing assays were also performed to determine the effect of c-di-GMP on lifespan of C. elegans. qRT-PCR was conducted to elucidate how c-di-GMP effects C. elegans gene expression levels involved in innate immunity. Results: CDNs produced by V. cholerae, specifically c-di-GMP, are playing an important role in the attraction of C. elegans towards V. cholerae. The chemoattraction of C. elegans towards c-di-GMP occurs in a concentration dependent manner. Through LC-MS results on V. cholerae, c- di-GMP was present extracellularly in concentrations similar to that observed in C. elegans attractive behavior toward that molecule. qRT-PCR results show that c-di-GMP treatment is playing a role in innate immunity in C. elegans by downregulating immune response genes that are normally active against V. cholerae infection. Through lifespan assays, it was also seen that continual presence of c-di-GMP significantly shortens the lifespan of C. elegans. Conclusion: This study further elucidates the role of c-di-GMP in interkingdom communication. Production of c-di-GMP causes an attractive behavior in C. elegans that in turn effects innate immunity and overall health of the organism.

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