Strains of Aspergillus niger and the related species A. awamori are used in the commercial production of secreted native and heterologous enzymes. Limitations on enzyme yield in fermenter growth are influenced by mycelial morphology, which affects mycelial density, energy input and oxygenation. While mutations affecting morphology can arise during strain improvement programmes, the ability to manipulate morphology during fermenter growth by controlled expression of a specific gene would be advantageous, since an appropriate vector could be introduced into any strain of A. niger by transformation. In order to demonstrate the feasibility of this approach, we have cloned part of the cotA gene of A. niger, a homologue of the Neurospora crassa cot-1 gene, and placed it under the control of the regulatable glaA promoter. The cot-1 mutation of Neurospora crassa is a temperature sensitive mutation in a serine-threonine protein kinase, and growth at the non-permissive temperature leads to loss of polar growth of hyphae and to hyperbranching as a result of loss of function. Using a vector designed for promoter replacement, transformants of A. niger were selected on maltose as carbon source, and were screened for growth morphology on xylose. Approximately 60% of transformants showed a compact morphology on xylose, which represses glaA, and were purified for further analysis. These transformants also showed a compact growth form in xylose liquid medium in shake flasks, but were normal in maltose medium. These strains will be analysed for growth characteristics in fermenters.
Full conference title:
21st Fungal Genetics Conference
- Fungal Genetics Conference 21st (2000)