Metabonomics reveals that entomopathogenic nematodes mediate tryptophan metabolites that kill host insects

The Emerging Role of 3-Hydroxyanthranilic Acid on C. elegans Aging Immune Function

3-hydroxyanthranilic acid (3HAA) is considered to be a fleeting metabolic intermediate along tryptophan catabolism through the kynurenine pathway. 3HAA and the rest of the kynurenine pathway have been linked to immune response in mammals yet whether it is detrimental or advantageous is a point of contention. Recently we have shown that accumulation of this metabolite, either through supplementation or prevention of its degradation, extends healthy lifespan in C. elegans and mice, while the mechanism remained unknown. Utilizing C. elegans as a model we investigate how 3HAA and haao-1 inhibition impact the host and the potential pathogens. What we find is that 3HAA improves host immune function with aging and serves as an antimicrobial against gram-negative bacteria. Regulation of 3HAA's antimicrobial activity is accomplished via tissue separation. 3HAA is synthesized in the C. elegans hypodermal tissue, localized to the site of pathogen interaction within the gut granules, and degraded in the neuronal cells. This tissue separation creates a new possible function for 3HAA that may give insight to a larger evolutionarily conserved function within the immune response.

Discovery of a new highly pathogenic toxin involved in insect sepsis

IMPORTANCE

As a current biocontrol resource, entomopathogenic nematodes and their symbiotic bacterium can produce many toxin factors to trigger insect sepsis, having the potential to promote sustainable pest management. In this study, we found Steinernema feltiae and Xenorhabdus bovienii were highly virulent against the insects. After infective juvenile injection, Galleria mellonella quickly turned black and softened with increasing esterase activity. Simultaneously, X. bovienii attacked hemocytes and released toxic components, resulting in extensive hemolysis and sepsis. Then, we applied high-resolution mass spectrometry-based metabolomics and found multiple substances were upregulated in the host hemolymph. We found extremely hazardous actinomycin D produced via 3-hydroxyanthranilic acid metabolites. Moreover, a combined transcriptomic analysis revealed that gene expression of proteins associated with actinomycin D was upregulated. Our research revealed actinomycin D might be responsible for the infestation activity of X. bovienii, indicating a new direction for exploring the sepsis mechanism and developing novel biotic pesticides.