Expression data from Aspergillus niger comparing aerial structures with vegetative mycelium

A. niger undergoes dramatic changes during asexual development. We tried to identify the differences in RNA expression levels that are important for this development. We used micro-arrays to determine which genes were up- or down-regulated in the aerial structures, the part of the colony that is formed during asexual development. A. niger was grown as a sandwiched culture (Wösten et al., 1991,Journal of General Microbiology 137: 2017–2023) in a 0.25 mm layer of 0.6 % agarose between two porous polycarbonate membranes (diameter 76 mm, pore size 0.1 µm; Profiltra; www.profiltra.nl). After six days of growth, the top membrane of the sandwich was replaced by a membrane with pores of 10 µm (Profiltra), allowing formation of aerial hyphae and conidiophores for 24 h. Vegetative mycelium and aerial structures of 7-day-old maltose-grown cultures of A. niger were harvested from 3 and 5 sandwiched colonies, respectively. The aerial structures were scraped from the top membrane of the sandwiched culture with a razor blade. From other colonies, vegetative mycelium was harvested by flipping over the top membrane and scraping it off with a razor blade.