Effect of carbohydrate type and concentration on polyhydroxy alcohol and trehalose content of conidia of three entomopathogenic fungi

Abstract

The entomopathogenic fungi Beauveria bassiana, Metarhizium anisopliae and Paecilomyces farinosus were cultured on solid agar media containing different carbohydrate components (glycerol, glucose, trehalose or starch) at concentrations of < 142.7 g added carbon I-1 for 30 d at 25 "C. The water activity ( a, ) of the media ranged from 0925 to 0.998. Growth of M. anisopliae and P. farinosus was stimulated between 0975 and 0.995 a , on glucose media and that of P. farinosus at 0.975 aw on glycerol media. At < 0.970 a , growth of each fungal species was significantly reduced (P < 0.05). Polyhydroxy alcohols (polyols) and trehalose were extracted from conidia produced on different media and quantified using HPLC. Total polyol content of conidia produced on glucose media varied between 5-2 and 52-2 mg g-l for B. bassiana, 77.3 and 903 mg g-l for M. anisopliae, and 26-7 and 76-1 mg g-l for P. farinosus. The amounts of specific polyols in conidia varied significantly from media of different glucose concentrations. Mannitol was the predominant polyol in conidia of all three species, with conidia of M. anisopliae, for example, containing as much as 75.2 mg mannitol g-l when cultured on glucose media. The amount of the lower molecular mass polyols glycerol and erythritol was greater in conidia produced on glucose media with > 500 g added carbon I-' than that in conidia produced at lower glucose concentrations. Conidia contained between 1 0 8 and 20.8 mg glycerol plus erythritol g-' on glucose media with 142-7 g added carbon I-', depending on species. Conversely, conidia of B. bassiana and P. farinosus contained maximum amounts of trehalose (d 23-5 mg g-l) when produced on glucose media with < 500 g added carbon I-l, and trehalose content was considerably less at higher glucose concentrations. There were accumulations of glycerol and erythritol in conidia of all three species when grown on glycerol media with > 25.0 g added carbon I-l; conidia of B. bassiana contained up to 1540 mg glycerol plus erythritol g-l. When B. bassiana and P. farinosus were grown on trehalose media, conidia contained up to 222.1 mg trehalose g-'. By contrast, conidia of M. anisopliae contained < 17.0 mg trehalose g-1 under all conditions tested. The water availability of solutions of different polyols is discussed in relation to their potential to act in osmotic adjustment during germination. The ability to manipulate polyol and trehalose content of fungal propagules may be critical in enhancing the storage life and efficacy of biological control agents.

Compatible Solutes Protect against Chaotrope(Ethanol)-Induced, Nonosmotic WaterStress

“…Glycerol and erythritol enhance conidial germination of several fungal species under NaCl-induced osmotic stress (8) and also have this effect on A. nidulans (Table 2). In contrast, mannitol is relatively ineffective as an osmoprotectant (2,4,7,8).…”

“…The glycerol and KCl concentrations employed were based on those used in previous studies (7,8). Petri plates were inoculated with 2-mm-diameter plugs of agar taken from the periphery of an exponential-phase culture growing on medium of the same composition.…”

Manipulation of intracellular glycerol and erythritol enhances germination of conidia at low water availability

“…Polyol and trehalose analyses were carried out on conidia that were wet and dry harvested (Hallsworth & Magan, 1994b). The polyol and trehalose content of wet harvested conidia was not significantly different ( P > 0.05) from that of dry-harvested conidia.…”

“…Hassan et a/., 1989). Furthermore, laboratory studies suggest that conidia containing high concentrations of glycerol and erythritol cause insect mortality more rapidly and at lower RH than normal propagules (Hallsworth & Magan, 1994~). Manipulation of intracellular polyols to accelerate germination and allow germination at low water availability may therefore improve the pathogenicity of fungal biocontrol agents in the field.…”

“…Accumulations of glycerol and/or erythritol occurred in conidia of B. bassiana, M. anisopliae and P. farinosw if cultures were grown at < 0.970 a, or supplied with a high concentration of glycerol (Hallsworth & Magan, 1994a, b). Initial studies suggested that conidia modified in this way are more pathogenic at low RH than those containing only trace amounts of glycerol and erythritol (Hallsworth & Magan, 1994~).…”