Impact of carbon and nitrogen nutrition on the quality, yield and composition of blastospores of the bioinsecticidal fungus Paecilomyces fumosoroseus

Abstract

The impact of growing cultures of Paecilomyces fumosoroseus in liquid media containing four combinations of glucose and casamino acids (8 g l⁻¹ or 80 g l⁻¹ glucose, 1.32 g l⁻¹ or 13.2 g l⁻¹ casamino acids) was evaluated, based on blastospore production, germination rate, viability after freeze-drying and short-term storage stability. When blastospores were produced using a high casamino acid concentration, blastospore yields and germination rates were significantly higher (13.2–18.5×10⁷ blastospores ml⁻¹, 50–60% germination after 4 h), compared to cultures grown in media containing lower casamino acid concentrations (0.4–2.3×10⁷ blastospores ml⁻¹, 10–20% germination after 4 h). Chemical analyses of blastospore composition showed that accelerated blastospore germination may be related to increased proteinaceous reserves rather than to glycogen or lipid accumulation. Tolerance to freeze-drying by blastospores suspended in spent medium was enhanced by a high initial casamino acid concentration in the culture medium (75% survival) and by the residual glucose concentrations in the spent medium. Under the conditions of this study, the storage stability of blastospores of P. fumosoroseus was unaffected by the nutritional condition in which they were produced.