Molecular genetics of the biocontrol agents Trichoderma spp.

We have developed conditions for an efficient method of genetic transformation for the biocontrol agents Trichoderma spp, using polyethylene glycol (PEG) and CaCl2 or high-voltage electroporation. Transformation was obtained with the plasmid pAN7–1 carrying a bacterial hygromycin resistance gene as a selectable marker under the control of Aspergillus nidulans heterologous expression signals. The system described here yielded 200 to 800 transformants per μg of DNA. Transformants contained several copies of the plasmid integrated into their genome, apparently at the same site in the different transformants analyzed. In the PEG-mediated transformation, stability of the transformants was achieved by inserting a 2.4-kb homologous DNA fragment into pAN7–1. DNA gel blot analysis indicated that integration in these stable transformants occurs through nonhomologous recombination