Influence of culture conditions on production and freeze-drying tolerance of Paecilomyces fumosoroseus blastospores

With the goal of developing a defined medium for the production of desiccat ion-tolerant blastospores of the bioinsecticidal fungus Paecilomyces fumoso roseus, we evaluated the impact of various media components such as amino a cids, carbohydrates, trace metals and vitamins on hyphal growth and sporula tion of P. fumosoroseus cultures and on the freeze-drying tolerance of blas tospores produced under these conditions. A comparison of 13 amino acids as sole nitrogen sources showed that glutamate, aspartate, glycine and argini ne supported biomass accumulations (12-16 mg ml(-1)) and blastospore yields (6-11 x 10(8) blastospores ml(-1)) comparable to our standard production m edium which contains casamino acids as the nitrogen source. Using glutamate as the sole nitrogen source, tests with various carbohydrates showed that P. fumosoroseus grew best on glucose (18.8 mg biomass ml(-1)) but produced similar blastospore concentrations (7.3-11.0 x 10(8)) when grown with gluco se, glycerol, fructose or sucrose, P. fumosoroseus cultures grown in media with sodium citrate or galactose as the sole carbohydrate produced lower bl astospore concentrations but more-desiccation-tolerant spores. Zinc was the only trace metal tested that-was required for optimal growth and sporulati on. In a defined medium with glutamate as the nitrogen source, vitamins wer e unnecessary for P. fumosoroseus growth or:sporulation. When blastospores were freeze-dried in the absence of a suspension medium, residual glucose ( >2.5% w/v) was required for enhanced spore survival. Thus, a defined medium containing basal salts, glucose, glutamate and zinc can be used to produce optimal concentrations of desiccation-tolerant blastospores of P. fumosoro seus.