Development of a homologous transformation system for Aspergillus niger based on the pyrG gene.

The development of a homologous transformation system for Aspergillus niger is described. The system is based on the use of an orotidine-5'-phosphate decarboxylase deficient mutant (pyrG) and a vector, pAB4-1, which contains the functional A. niger pyrG gene as a selection marker. Transformation of the A. niger pyrG mutant with pAB4-1 resulted in the appearance of stable Pyr+ transformants at a frequency of 40 transformants per microgram of DNA. In 90% of these transformants integration had occurred at the resident pyrG locus, resulting either in replacement of the mutant allele by the wild-type allele (60%) or in insertion of one or two copies of the vector (40%). The A. niger pyrG mutant could also be transformed with the vector pDJB2 containing the pyr4 gene of Neurospora crassa, at a frequency of 2 transformants per microgram of DNA. Integration at the resident pyrG locus was not found with this vector. The vector pAB4-1 is also capable of transforming an Aspergillus nidulans pyrG mutant to Pyr+. The pyrG transformation system was used for the introduction of a non-selectable gene into A. niger.