Downloaded from www.microbiologyresearch.org by IP: 54.242.161.225 On: Sun, 01 May 2016 16:04:06 Microbiology (1994), 140, 2705-2713 Printed in Great Britain Effect of carbohydrate type and concentration on polyhydroxy alcohol and trehalose content of conidia of three entornopathogenic fungi John E. Hallswortht and Naresh Magan Author for correspondence: John E. Hallsworth. Tel: +44 31 449 5111. Fax: +44 31 451 3009. ~~ ~ Biotechnology Centre, Cranfield University, Cranfield, Bedford MK43 OAL, UK 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 108 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. Keywords : entornopathogenic fungi, polyhydroxy alcohol, trehalose, conidia, water activity INTRODUCTION conidia are unable to germinate because water availability Fungal biological control agents can be ineffective if is suboptimal (Walstad et QL., 1970; Ferron, 1977; . . . ......... . .. . . . , . . . . . ,,,, . , . ,, . . , . . .. . ... . . .... . .. . . . . . . ,,,, . .... . .... , . . . . . . . . . . . . .. . . ... . . ... . . ... . . .. . . . .. . .. , . . . , .. . . .. . . . . . . .. . . . . . . . . ..... . Doberski, 1981 ; Gillespie & Crawford, 1986; Hsiao et al., t Present address: Department of Biological Sciences, Heriot-Watt Uni- 1992) 01 if they have inadequate carbohydrate reserves versity, Riccarton, Edinburgh EH14 4AS, UK. (Lane et al., 1991a; Harman et al., 1991). One way to Abbreviation : a , , water activity. overcome these problems is to modify the carbohydrate 0001-8961 0 1994SGM 2705