Aims: The objective of this study was to develop a novel synthetic growth medium for increased conidium production of the entompathogenic fungus Metarhizium anisopliae. The medium should simulate natural nutritional conditions.
Methods and results: Macro- and micronutrients were selected in concentrations found in insects or from sources which are believed to be advantageous for virulence. Medium development was guided by a problem-oriented genetic algorithm (GA) implemented with 'mutation' and 'recombination' operators specific for this optimization problem. Following five optimization steps and a total of 181 medium variations, 19 synthetic media led to increased conidium production as compared with the standard Sabouraud dextrose agar medium: increases in conidia yields of up to 120% and a 17-fold higher conidium production per square centimetre of mycelium were achieved. Rapid germination of conidia, conidial C : N ratio, as well as spore-bound Pr1 protease production were monitored as proposed quality control markers for a virulent inoculum.
Conclusions: It was demonstrated that our problem-oriented GA is a powerful tool for the design of chemically defined cultivation media with special/enhanced properties for anamorphic fungi.
Significance and impact of the study: This is the first study, which demonstrates the advantage of the use of a GA for the rapid design of solid synthetic media for maximum production of virulent conidia.