Effects of water activity on morphology, growth and blastospore production of Metarhizium anisopliae, Beauveria bassiana and Paecilomyces farinosus in batch and fed-batch culture

Abstract

Metarhizium anisopliae, Beauveria bassiana and Paecilomyces farinosus were grown in submerged liquid culture on glucose- and polyethylene glycol (PEG)-adjusted media of different initial water activities. The initial glucose or PEG concentration of the medium affected the morphology, biomass and blastospore production of M. anisopliae and P. farinosus in shake flask culture. At 80 mg glucose ml−1 or 0·15 M PEG (initial water activity (aw), 0·980), M. anisopliae grew filamentously, but at 10 mg glucose ml−1 or in the absence of PEG (initial aw, 0·986), pellet growth occurred. Similarly, less mycelial aggregation occurred in cultures of P. farinosus grown at low (aw, 0·982) than at high (aw, 0·990) initial water activities. Conditions which favoured a filamentous morphology were correlated with increased blastospore production. Blastospore yield of fed-batch cultures of B. bassiana was increased when the water activity of the nutrient feed was reduced by the incorporation of 2·4 M PEG.