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.
1. Identification of major insect pathogenic fungi completed. The insect pathogenic species of Beauveria is one of the largest groups of insect pathogenic fungi distributed worldwide, of which several species have been developed as commercial formulations. As such, the correct identification of isolates is an important component in their evaluation. ARS researchers at Ithaca, NY, and Beltsville, MD, have completed the revision of the species relationships of Beauveria, and the manuscript presenting this data has been accepted for publication in Mycologia. This work has significantly revised and augmented the previously recognized identifications within this important and ubiquitous insect pathogenic fungus group and should be of great use for proper classification of these important biocontrol agents.
2. New website for disseminating the Insect Pathogenic Fungal Culture Collection (ARSEF). ARS researchers at Ithaca, NY, have completed a revised website for the ARS Collection of Insect Pathogenic Fungi (ARSEF) for the public. The website provides two fully indexed set of catalogs that present all available fungi and other limited sets of the most requested isolates from the ARSEF culture collection. The ARSEF collection website also includes a complete listing of nearly 140 publications available as downloadable PDF files as well as other pertinent information. The new website should improve customer usage and access to information useful for researchers in biological control.
3. Genome sequence completed for the major insect pathogen Metarhizium robertsii. ARS researchers at Ithaca, NY, have completed the sequencing and assembly of the Metarhizium robertsii ARSEF 2575 genome. This information can now be used to compare to two recently published genomes of related Metarhizium species to reveal any unique differences that drive the association between insect-pathogenic fungi and their hosts and to shed light on the specific factors that impact survival, development, virulence, and pathogenicity.
4. Ability to hydrolyze biomass reflected in host specificity of pathogenic fungi. ARS researchers at Ithaca, NY, together with Cornell university researchers, have completed a survey of a broad range of plant pathogenic fungi for their ability to degrade different types of plant biomass and isolated polysaccharides. Among moderately and highly active species, plant pathogenic species were found to be more active than non-pathogens. Greater hydrolysis was seen when pathogens were tested on biomass and polysaccharides derived from plant biomass from their known host plants (biomass from grasses or dicots such as alfalfa or soybean). These results, published in Biotechnology for Biofuels, show that many plant pathogenic fungi are highly competent producers of enzymes useful to digest plant biomass and are promising sources from which to find accessory enzymes for optimizing bioenergy conversion from biomass substrates.
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.