Sporulation inhibited secretion in Aspergillus niger

Aspergillus niger is abundantly found in nature. It degrades dead material of plants and animals but can also be a pathogen of these organisms. Aspergillus niger is also important for mankind because it is one of the main organisms used for the industrial production of enzymes. These enzymes are released into the culture medium, from which they can be easily isolated. I have shown for the first time in a quantitative way that different zones of colonies of Aspergillus niger release different enzymes. This finding is instrumental in understanding how fungi degrade organic substrates in nature. Notably, I identified a zone in colonies that does not secrete proteins. This zone has the capacity to reproduce asexually. This suggested that sporulation inhibits secretion of proteins. Indeed, inactivation of the sporulation genes flbA, and fluG results in protein secretion throughout the mycelium. Inactivation of flbA also resulted in more protein release in the medium, which is partly explained by the thinner cell walls of this mutant. Thinner cell walls were also obtained by adding the antibiotic cycloheximide to the culture medium. This also resulted in increased protein release. Secreted proteins are easily trapped in a thicker cell wall, or might associate with cell wall components compared to hyphae with thinner cell walls. Therefore, a colony that forms hyphae with thin cell walls will release high amounts of protein in the culture medium. This finding and the fact that sporulation inhibits protein release is of interest for the industry to improve A. niger as a cell factory