( II as illustrated by Lemke and Peng 1...)Transformation of Filamentous Fungi by Microprojectile Bombardment

Conclusions
Aspergillus nidulans conidia are an ideal target for transformation by microprojectile bombardment due to their uninucleate character and the ease with which conidial density can be controlled and transformants selected and quantified. Since A. nidulans conidial suspensions are a heterogeneous mixture of spores (with a minimum diameter of 3 m and various stages of maturity, cell wall thickness and composition), and tungsten particles are extremely heterogeneous in size, similar transformation frequencies over a relatively wide range of conditions might not be surprising. These findings are consistent with the study by Lorito et al . (1993) who demonstrated that the number of conidia per plate significantly affected transformation efficiency of T. harzianum and G. virens conidia, whereas changes in the helium pressure (800 vs. 1,200 psi) did not affect transformation efficiencies. Bombardment conditions optimized for T. harzianum and G. virens are compared in Table 2. Transformation frequencies for each of these species by particle bombardment or chemical transformation were comparable (Lorito et al ., 1993; Herzog et al ., 1996). Integration of several copies of the entire plasmid at multiple sites and/or as tandem repeats, as evident from the Southern blot, was found to be the predominant fate of introduced DNA in stable transformants for both conidia transformed by particle bombardment and protoplasts transformed by PEG-mediated transformation (Figure 3, lanes 39; Waring et al ., 1989).

These results show that microprojectile bombardment is a very efficient
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