TRANSFORMATION OF INTACT ASPERGILLUS-NIGER BY ELECTROPORATION

A new rapid transformation system for Aspergillus niger that uses elec troporation to render intact germinating conidia permeable to DNA is d escribed. The transformant colonies appeared earlier than transformant s obtained by the protoplast-forming method. Without pretreatment of t he conidia the transformation frequencies were 1.2 colonies per mu g o f integrative vector and 100 colonies per mu g of plasmid DNA. When th e conidia were treated with a dilute solution of fungal cell wall lyti c enzyme, the frequency of transformation was increased by approx, 2-f old when using two vectors. Southern blot analysis of genomic DNA and restriction endonuclease-digested DNA from a random sample of transfor mants showed homologous and nonhomologous integration of the integrati ve vector into the genome, as is also observed with the protoplast-for ming method. In transformation with the plasmid vector, the transforma nt DNA was shown to be mostly maintained in free form with minimal int egration into the chromosome when transformed by either intact electro poration or the conventional method.