Effects of KCl concentration on accumulation of acyclic sugar alcohols and trehalose in conidia of three entomopathogenic fungi



Beauveria bassiana, Metarhizium anisopliae and Paecilomyces farinosus were grown on Sabouraud Dextrose Agar (SDA) modified with KCl to give a range of water activity (aw) from 0.938 to 0.998. Growth of all three species was optimal at 0.983 aw and growth occurred over the aw range tested. Acyclic sugar alcohol (polyol) and trehalose content of conidia was determined by HPLC and found to vary with species and aw. Conidia of B. bassiana and P. farinosus were found to contain totals of 1.5% and 2.3% polyols respectively at 0.998 aw, and double these amounts at <0.950 aw. Conidia of M. anisopliae contained from 5.7% to 6.8% polyols at each aw tested. In conidia of all three species the predominant polyol was mannitol. The lower molecular weight polyols, arabitol and erythritol, were found to accumulate at reduced aw. Small amounts of glycerol were present in conidia of each species; <15% total polyols. Conidia of B. bassiana and M. anisopliae contained about 0.5% trehalose from 0.970 to 0.998 aw, but only trace amounts below 0.950 aw. Conidia of P. farinosus contained 2.1% trehalose at 0.998 aw and this decreased to <0.1% below 0.950 aw. Potential to manipulate the endogenous reserves of conidia of these biological control agents to enhance viability and desiccation toierance is discussed