PhD defence: Genes involved in growth and sporulation in Aspergillus niger

The fungus Aspergillus niger breaks down organic waste in nature, is a pathogen of plants and animals, but can also make a positive contribution to the growth of plants. It is also a human pathogen and spoils food, but on the other hand it is extensively used for the industrial production of enzymes and metabolites such as citric acid.

The formation of spores, called conidia, is an important factor why A. niger is such a successful fungus in nature. A single colony of this fungus can produce more than a billion conidia in a few days. The spread and germination of these spores mark the beginning of the colonization of dead and living organisms.

The gene flbA is known to be involved in suppressing vegetative growth while stimulating sporulation. Inactivation of flbA results not only in a non-sporulating colony but also in a thinner, more fragile cell wall, and more and a greater diversity of proteins are secreted. As such, flbA is an important regulatory protein.

FlbA from A. niger regulates a total of 36 transcription factor (TF) genes, of which only 9 had been characterized at the start of my PhD research. I have characterized 13 other flbA-regulated genes (abaA, aslA, aslB, azf1, htfA, nosA and srbA, socA, dofA, dofB, dofC, dofD and flbD) that were shown to be involved in spore production and, with the exception of abaA, in protein secretion and/or cell wall integrity. In addition, I investigated the role of the flbB, flbC and flbE proteins of A. niger. Like flbA, inactivation of these genes in A. niger results in colonies impaired in cell wall stress (flbB, flbC, flbE) and sporulation (flbB, flbC).