Dominant Selectable Markers for Penicillium spp. Transformation and Gene Function Studies

Penicillium spp. has been genetically manipulated and gene function studies have utilized single gene deletion strains for phenotypic analysis. Fungal transformation experiments have relied on hygromycin and hygromycin phosphotransferase (hph) as the main dominant selectable marker (DSM) system in Penicillium spp. This poses a limitation on the number of loci that can be analyzed and complemented in reverse genetic studies. Additionally, many economically important Penicillium spp. have not been evaluated to determine the utility of additional chemicals that can serve as DSMs. Therefore, six compounds were examined for 15 blue mold strains and their Minimum Inhibitory Concentrations (MICs) determined. Phleomycin, neomycin and G418 were deemed ineffective, as Penicillium spp. growth was observed on media amended with 1000 μg/ml of each compound. The efficacy of bialophos to inhibit fungal growth was intermediate, with MICs ranging from 250 to 1000 μg/ml and was species-dependent. However, chlorimuron ethyl and benlate had the lowest MIC values and minimal variation in efficacy within and between species. Therefore, benlate and chlorimuron ethyl are good candidates for use as since corresponding fungal resistance genes have been cloned, characterized and are available from a variety of public and academic sources.