Unknown,Transcriptomics,Genomics,Proteomics

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Expression data from Aspergillus niger comparing aerial structures with vegetative mycelium

ABSTRACT: 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.

ORGANISM(S): Aspergillus niger

SUBMITTER: R Bleichrodt

PROVIDER: E-GEOD-32123 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:This work presents an exploration of submerged differentiation of the ubiquitous saprophyte and industrially important fungus, Aspergillus niger, in response to a limited availability of a sole carbon and energy source, maltose. In aspergilli and other mold fungi, asexual reproduction through formation of elaborate conidiogenic structures normally requires an aerial interface. This requirement is bypassed in submerged culture in response to severe nutrient limitation. Continuous cultures with cell retention (retentostat cultures) were applied to generate a fundamental physiological state, where the specific growth rate approaches zero, as the density of the cell population adapts to the supply of the limiting energy source. Temporal differentiation of mycelium structure and commitment to asexual reproduction were major phenomena, apparent on biochemical, morphological, physiological, and transcriptomic level. The severe substrate limitation had a rapid negative impact on cytoplasmic processes, and promoted endo- and exogenous nutrient mobilization, and hyphal compartmentalisation. The first conidiogenic structures appeared after one day with little additional differentiation until Day 4 to 6, where a transition to full commitment to reproductive growth took place. Submerged conidiation in A. niger involved transcriptional regulation of homologs of the regulatory pathway, centered around the Bristle gene (brlA), and structural genes previously described in other aspergilli. Comparison of transcriptomes, revealed a number of co-regulated gene clusters, which appear to encode secondary metabolite biosynthetic potential. We discuss the concept of maintenance energy in the context of differentiation, a possible physiological trigger for sporulation and the special physiological adaptations of the starved mycelium. We also present a simple and efficient method for in situ retention of filamentous organisms. The dataset consists of 9 Affymetrix arrays derived from defined growth conditions of lab-scale bioreactor cultures (5L). Total RNA was extracted from biomass harvested at three different growth phases: exponential growth phase, 2 and 8 days of retentostat cultivation. For each of the phases, the data is derived from three biological replicates.