P9: Improving Aspergillus niger as cell factory for heterologous protein production through transcription factor modulation

Aspergillus niger is widely exploited for production of native and heterologous proteins. However, the yields of heterologous proteins are often low, indicating the need for strain improvement. This can be achieved by increasing the level of heterologous protein expression, but an alternative approach could be reduction of protease activities. Production of heterologous proteins is often coupled to growth because of the applied promoters and this makes faster growth an attractive parameter. Furthermore, faster growth lowers the cultivation time which ultimately lowers the production cost.

Altering pathways controlled by complex regulation as the proteolytic system in A. niger can be troublesome. Deleting a single or few genes in the complex systems is usually of limited success. Thus, targeting the overall regulators, e.g. transcription factors, there is potential for altering several pathways and overcome the challenges in regulation and this approach can therefore provide an alternative tool for metabolic engineering.

In the present study, a method applying transcription factor modulation through carefully selected transcription factors will be described. Two mutants with a phenotype especially suitable for protein production were identified. MUT1 had a fast growing phenotype. In bioreactors, 2L scale MUT1 showed 28% (±4%) increased in µmax together with a 46 % increase in the overall biomass yield and a 45%  deceased production of oxalic acid. MUT2 had a reduced secreted extracellular protease phenotype. With protease activity decreased 41% combined with 89% deceased production of oxalic acid. These phenotypes give these strains a high potential as a protein cell factory.