Location: Emerging Pests and Pathogens Research2011 Annual Report
1a. Objectives (from AD-416)
1. Culture, conserve, characterize, and exchange insect pathogenic fungi, fungal genetic resources and associated information from the ARS Collection of Entomopathogenic Fungal Cultures (ARSEF). 2. Develop molecular tools of functional genomics for use in systematics and in defining secondary metabolites and products of insect pathogenic fungi that affect biological control potential. 3. Discover natural fungal metabolites and products to evaluate their roles in the survival, development, virulence, and pathogenicity of fungal biological control agents. 4. Identify and characterize novel lead chemistries for the development of new fungal metabolite-based pesticides for agricultural applications.
1b. Approach (from AD-416)
Use various preservation methods (lyophil, cryogenic, offsite backup) to maintain culture collection and to accession new germplasm for customer base. Develop new methods to isolate, culture, and preserve isolates. Conduct studies on the systematics, taxonomy, and organismal biology of these fungi. Use molecular and bioinformatic tools to evaluate insect pathogenic genomes and gene families. Use molecular tools to target secondary metabolite pathways. Characterize biological activity and chemistries of compounds produced by fungi at various developmental stages.
3. Progress Report
Holdings of ARS Collection of Entomopathogenic Fungal Cultures (ARSEF). In the last 12 months, the ARSEF culture collection has accessioned 1068 isolates, received several hundred more cultures awaiting formal accessioning and long-term preservation, and distributed 454 cultures in response to 87 requests. ARSEF currently comprises 11061 accessions of 673 fungal taxa from 2210 locations worldwide, and 1259 different hosts and substrates. Accession information for ARSEF holdings continues to be revised as molecular reidentifications are received. Identification of Novel Cytotoxic Metabolite Expressed by Biocontrol Agent. The insect pathogenic fungus Metarhizium acridum has a host-range limited to grasshoppers of which two strains have been commercially developed for insect control. Although this species has been reported to have few secondary metabolites, we characterized two novel conidial-derived factors as new macrocyclic amidolactones, metacridamides A and B, in addition to the previously discovered serinocyclins. The metacridamides had no activity in insecticidal, antimicrobial, and phytoxicity assays, but they did possess moderate cytotoxicity against a number of cancer cell lines. Although the biological relevance of this activity is unclear, it provides support for the concept of secondary metabolites having a subtler role in mediating host-pathogen interactions. Analysis of Major Metabolite Gene in Metarhizium robertsii. Destruxins are among the most exhaustively researched secondary metabolites of insect pathogenic fungi. We identified the gene cluster responsible for their biosynthesis in order to generate knockout strains incapable of producing destruxins. The mutants had no significant changes in virulence levels against larvae of Spodoptera exigua and no changes in morphology and development. Gene expression was detectable at low levels during early growth phase and increased with culture time, and gene transcripts were also detectable in later stages of infected insects and in conidia. The destruxins appear to be dispensable for virulence against S. exigua, casting doubt on their long-purported role in insect pathogenicity and virulence.
Gibson, D.M., King, B.C., Hayes, M.L., Bergstrom, G.C. 2011. Plant pathogens as a source of diverse enzymes for lignocellulose digestion. Current Opinion in Microbiology. 14(3):264-270.