Submitted to: Society for Invertebrate Pathology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: July 18, 2013
Publication Date: August 11, 2013
Citation: Gibson, D.M., Donzelli, B.G., Krasnoff, S. 2013. Are secondary metabolites dispensable for virulence?. Society for Invertebrate Pathology Annual Meeting. 9:82. Technical Abstract: The production of toxins by conidial fungal pathogens and their association with virulence has been assumed to occur in vivo and is widely accepted as dogma, but this association has yet to be definitively proven by either genetic or chemical means. Several studies from our labs have used targeted gene disruption approaches to directly address the role of secondary metabolites (SM) in insect pathogenesis, using Metarhizium robertsii ARSEF 2575. Knock out mutants for three distinct secondary metabolite pathways- destruxins, the fusarin analogs NG391/NG393, and the conidia-localized serinocyclins- showed wild-type level virulence against several insect host species. No phenotypic differences in morphology, growth, development or response to oxidative stress were exhibited by the knockout strains. These findings are in stark contrast to the outcome predicted by a large body of in vitro toxicological studies suggesting SMs, such as the destruxins, are key virulence factors for Metarhizium invertebrate pathogens. We suggest that the relationship of SMs to virulence may be coincidental, and the compounds may play roles in other unknown functions, or cause subtle effects in the host, not measurable with traditional pathogenicity assays. However, given the range of potentially detrimental activities reported for these SMs, including mutagenicity, ionophoresis, and cytotoxicity, their potential risk as environmental contaminants or pollutants remains a concern and the availability of SM- strains that retain virulence against insects provides a pool from which to draw for the engineering of safe and effective biocontrol strains.