EFFECTS OF MEDIA COMPOSITION ON METARHIZIUM ANISOPLIAE VAR. ACRIDUM SPORES, PART 2: EFFECTS OF MEDIA OSMOLALITY ON CELL WALL CHARACTERISTICS, CARBOHYDRATE CONCENTRATIONS, DRYING STABILITY, AND PATHOGENICITY.

Authors: Leland, Jarrod; MULLINS, DONALD - VIRGINIA TECH; VAUGHAN, LARRY - VIRGINIA TECH; WARREN, HERMAN - VIRGINIA TECH

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2004
Publication Date: 6/4/2005
Citation: Leland, J.E., Mullins, D.E., Vaughan, L.J., Warren, H.L. 2005. Effects of media composition on metarhizium anisopliae var. acridum spores, part 2: effects of media osmolality on cell wall characteristics, carbohydrate concentrations, drying stability, and pathogenicity.. Biocontrol Science and Technology.

Interpretive Summary: Fungal spores that kill insects may be produced in liquid culture and the composition of the liquid in which they are grown may affect the spores' characteristics. These spore characteristics effect the usefulness of these spores for controlling insect pests. Components may be added to the liquid which make water less available to the spores and cause changes in spore structure to retain nutrients. Spores grown in liquid containing these components were compared to spores grown in liquid lacking these components. The structure of the spores and the properties of their outer surfaces were compared. Performance characteristics, such as how fast the spores germinate, how well they survive drying, and how well they kill insects were compared. This study showed that by adding these components to the liquid in which spores were grown, the spores were better able to survive drying and kill insects. This may have practical application for improving the economics of spore production, producing spores that can survive drying, and improving insect control.

Technical Abstract: This study evaluates the relationships among media osmolality of a submerged conidia-producing medium and spore production, spore morphology (dimensions and cell wall structure), chemical properties of cell wall surfaces (charge, hydrophobicity, and lectin binding), spore contents of polyols and trehalose, and spore performance characteristics (drying stability and pathogenicity). Spore production was increased by the addition of up to 150 g/L polyethylene glycol 200 (PEG), which corresponded with a reduction in mycelial pellet formation. Spores from high osmolality medium containing 100 g/L PEG (HOM spores) had thin cell walls and dimensions more similar to blastospores than submerged conidia or aerial conidia. However, a faint electron-dense layer within HOM spores' cell walls was discernable by transmission electron microscopy indicating the presence of a double-layered cell wall. HOM spores also appeared to have an outer rodlet layer, unlike blastospores, although it was thinner than those observed in submerged conidia. HOM spores' surfaces possessed hydrophobic microsites, which was further evidence of the presence of a rodlet layer. In addition, HOM spores had concentrations of exposed n-acetyl- -D-glucosaminyl residues intermediate between blastospores and submerged conidia, which may be related to the masking of underlying cell wall by a rodlet layer. All spore-types had exposed -D-mannosyl and/or -D-glucosyl residues, but lacked oligosaccharides. HOM spores were less anionic than submerged conidia, similar to blastospores. Although HOM spores had thin cell walls, they were more stable to drying than blastospores and submerged conidia. Relative drying stability did not appear to be the results of differences in polyol or trehalose concentrations between submerged conidia and HOM spores. HOM spores had faster germination rates than submerged conidia, similar to blastospores, and they were more pathogenic to Schistocerca americana than submerged conidia and aerial conidia.