Improved transformation efficiency of Aspergillus niger using the homologous niaD gene for nitrate reductase

Abstract
Aspergillus niger transformation frequencies of up to 1,176 transformants per μg DNA were achieved using the plasmid vector pSTA10 containing the A. niger nitrate reductase structural gene. Analysis of genomic endonuclease cleaved DNA from nitrate utilising transformants by DNA hybridisation, showed that most integration events are as a result of homologous recombination. The niaD transformation system was used successfully for the introduction of the unselected Escherichia coli fusion genes lacZ, encoding β-galactosidase, and uidA, for β-glucuronidase, as well as the Neurospora crassa tub-2 gene, for β-tubulin. pSTA10 was also capable of transforming niaD mutants of other filamentous fungi such as A. nidulans, A. oryzae and Penicillium chrysogenum.