Sulfonylurea resistance as a new selectable marker for the entomopathogenic fungus Beauveria bassiana

Beauveria bassiana is a filamentous ascomycete that is pathogenic towards a broad host range of insect targets and is increasingly serving as a model for examining fungal development and host-pathogen interactions. B. bassiana displays a prohibitive level of resistance against many current fungal and/or yeast selection markers including hygromycin, neomycin, and zeocin. A genetic transformation system for B. bassiana based upon the use of a sulfonylurea resistance cassette derived from the Magnaporthe grisea, acetolactate synthase gene (sur) was developed. The transformation frequency ranged from 100–150 transformants per microgram DNA/10⁸ cells and Southern blot analysis indicated that the plasmid vector was randomly integrated into the genome of B. bassiana. In addition, a construct bearing the sur gene and the enhanced green fluorescent protein gene egfp as a visual marker was used to successfully transform B. bassiana. Over 95% of the transformants retained the sulfonylurea resistance phenotype under non-selective conditions. The described transformation method increases opportunities for the genetic manipulation of B. bassiana.