Functionality of heterogeneity in size of Aspergillus niger micro-colonies

The fungus Aspergillus niger secretes a wide variety and high amounts of enzymes to degrade organic material. Its secretion capacity is important for nutrient recycling in nature and is used for industrial protein production. A. niger forms micro-colonies of different size when grown in a liquid medium such as in bioreactors. We here described that the secretomes of the small and large micro-colonies have a different composition and complementary activities. On the other hand, we here show that the large micro-colonies are more resistant to heat and hydrogen peroxide stress. Experimental data indicate that this higher resistance is due to the presence of non-germinated spores in the centre of large micro-colonies (and that are absent in small micro-colonies) and by the protection of these spores and hyphae in the centre by hyphae at the micro-colony periphery. Together, A. niger improves its fitness by forming micro-colonies that are heterogeneous in size. Besides, We also found that biomass formation, spore swelling and germ tube formation of strains with a less active orotidine 5'-phosphate decarboxylase gene pyrG is unaffected when compared to wild-type. In contrast, strains with a less active pyrG form smaller micro-colonies, probably due to reduced spore aggregation. Cellular proteomics revealed candidate genes that may be involved in this difference in spore aggregation, and it also shows that changed morphology impacts the secretome.