Dataset Information

The carbon starvation response of Aspergillus niger during submerged cultivation: insights from the transcriptome and secretome.

ABSTRACT: BACKGROUND: Filamentous fungi are confronted with changes and limitations of their carbon source during growth in their natural habitats and during industrial applications. To survive life-threatening starvation conditions, carbon from endogenous resources becomes mobilized to fuel maintenance and self-propagation. Key to understand the underlying cellular processes is the system-wide analysis of fungal starvation responses in a temporal and spatial resolution. The knowledge deduced is important for the development of optimized industrial production processes. RESULTS: This study describes the physiological, morphological and genome-wide transcriptional changes caused by prolonged carbon starvation during submerged batch cultivation of the filamentous fungus Aspergillus niger. Bioreactor cultivation supported highly reproducible growth conditions and monitoring of physiological parameters. Changes in hyphal growth and morphology were analyzed at distinct cultivation phases using automated image analysis. The Affymetrix GeneChip platform was used to establish genome-wide transcriptional profiles for three selected time points during prolonged carbon starvation. Compared to the exponential growth transcriptome, about 50% (7,292) of all genes displayed differential gene expression during at least one of the starvation time points. Enrichment analysis of Gene Ontology, Pfam domain and KEGG pathway annotations uncovered autophagy and asexual reproduction as major global transcriptional trends. Induced transcription of genes encoding hydrolytic enzymes was accompanied by increased secretion of hydrolases including chitinases, glucanases, proteases and phospholipases as identified by mass spectrometry. CONCLUSIONS: This study is the first system-wide analysis of the carbon starvation response in a filamentous fungus. Morphological, transcriptomic and secretomic analyses identified key events important for fungal survival and their chronology. The dataset obtained forms a comprehensive framework for further elucidation of the interrelation and interplay of the individual cellular events involved.

SUBMITTER: Nitsche BM

PROVIDER: S-EPMC3527191 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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The carbon starvation response of Aspergillus niger during submerged cultivation: insights from the transcriptome and secretome.

Nitsche Benjamin M BM Jørgensen Thomas R TR Akeroyd Michiel M Meyer Vera V Ram Arthur F J AF

BMC genomics 20120808

<h4>Background</h4>Filamentous fungi are confronted with changes and limitations of their carbon source during growth in their natural habitats and during industrial applications. To survive life-threatening starvation conditions, carbon from endogenous resources becomes mobilized to fuel maintenance and self-propagation. Key to understand the underlying cellular processes is the system-wide analysis of fungal starvation responses in a temporal and spatial resolution. The knowledge deduced is im ...[more]

PMID: 22873931

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Project description:Filamentous fungi are confronted with changes and limitations of their carbon source during growth in their natural habitats and during industrial applications. To survive life-threatening starvation conditions, carbon from extra- and intracellular resources becomes mobilized to fuel fungal self-propagation. Key to understand the underlying cellular processes is the system-wide analysis of fungal starvation responses in a temporal and spatial resolution. The knowledge deduced is important for the development of optimized industrial production processes. This study describes the physiological, morphological and genome-wide transcriptional changes caused by prolonged carbon starvation during submerged batch cultivation of the filamentous fungus Aspergillus niger. Bioreactor cultivation supported highly reproducible growth conditions and monitoring of physiological parameters. Changes in hyphal growth and morphology were analyzed at distinct cultivation phases using automated image analysis. The Affymetrix GeneChip platform was used to establish genome-wide transcriptional profiles for three selected time points during prolonged carbon starvation. Compared to the exponential growth transcriptome, about 50% (7,292) of all genes displayed differential genes expression during at least one of the starvation time points. Enrichment analysis of Gene Ontology, Pfam domain and KEGG pathway annotations uncovered autophagy and asexual reproduction as major global transcriptional trends. Induced transcription of genes encoding hydrolytic enzymes was accompanied by increased secretion of hydrolases including chitinases, glucanases, proteases and phospholipases as identified by mass spectrometry. This study is the first system-wide analysis of the carbon starvation response in a filamentous fungus. Morphological, transcriptomic and secretomic analyses identified key events important for fungal survival and their chronology. The dataset obtained forms a comprehensive framework for further elucidation of the interrelation and interplay of the individual cellular events involved.

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.

Project description:In nature, filamentous fungi are exposed to diverse nutritional sources and changes in substrate availability. Conversely, in submerged cultures, mycelia are continuously exposed to the existing substrates, which are depleted over time. Submerged cultures are the preferred choice for experimental setups in laboratory and industry and are often used for understanding the physiology of fungi. However, to what extent the cultivation method affects fungal physiology, with respect to utilization of natural substrates, has not been addressed in detail. Here, we compared the transcriptomic responses of Aspergillus niger grown in submerged culture and solid culture, both containing sugar beet pulp (SBP) as a carbon source. The results showed that expression of CAZy (Carbohydrate Active enZyme)-encoding and sugar catabolic genes in liquid SBP was time dependent. Moreover, additional components of SBP delayed the A. niger response to the degradation of pectin present in SBP. In addition, we demonstrated that liquid cultures induced wider transcriptome variability than solid cultures. Although there was a correlation regarding sugar metabolic gene expression patterns between liquid and solid cultures, it decreased in the case of CAZyme-encoding genes. In conclusion, the transcriptomic response of A. niger to SBP is influenced by the culturing method, limiting the value of liquid cultures for understanding the behavior of fungi in natural habitats. IMPORTANCE Understanding the interaction between filamentous fungi and their natural and biotechnological environments has been of great interest for the scientific community. Submerged cultures are preferred over solid cultures at a laboratory scale to study the natural response of fungi to different stimuli found in nature (e.g., carbon/nitrogen sources, pH). However, whether and to what extent submerged cultures introduce variation in the physiology of fungi during growth on plant biomass have not been studied in detail. In this study, we compared the transcriptomic responses of Aspergillus niger to growth on liquid and solid cultures containing sugar beet pulp (a by-product of the sugar industry) as a carbon source. We demonstrate that the transcriptomic response of A. niger was highly affected by the culture condition, since the transcriptomic response obtained in a liquid environment could not fully explain the behavior of the fungus in a solid environment. This could partially explain the differences often observed between the phenotypes on plates compared to liquid cultures.

Project description:The nutrient digestibility and feeding value of rapeseed meal (RSM) for non-ruminant animals is poor due to the presence of anti-nutritional substances such as glucosinolate, phytic acid, crude fiber etc. In the present study, a solid state fermentation (SSF) using Aspergillus niger was carried out with the purpose of improving the nutritional quality of RSM. The chemical composition and physicochemical properties of RSM before and after fermentation were compared. To further understand possible mechanism of solid state fermentation, the composition of extracellular enzymes secreted by Aspergillus niger during fermentation was analysed using two-dimentional difference gel electrophoresis (2D-DIGE) combined with matrix assisted laser desorption ionization-time of flight-mass spectrometer (MALDI-TOF-MS). Results of the present study indicated that SSF had significant effects on chemical composition of RSM. The fermented rapeseed meal (FRSM) contained more crude protein (CP) and amino acid (AA) (except His) than unfermented RSM. Notably, the small peptide in FRSM was 2.26 time larger than that in unfermented RSM. Concentrations of anti-nutritional substrates in FRSM including neutral detergent fiber (NDF), glucosinolates, isothiocyanate, oxazolidithione, and phytic acid declined (P < 0.05) by 13.47, 43.07, 55.64, 44.68 and 86.09%, respectively, compared with unfermented RSM. A. niger fermentation disrupted the surface structure, changed macromolecular organic compounds, and reduced the protein molecular weights of RSM substrate. Total proteins of raw RSM and FRSM were separated and 51 protein spots were selected for mass spectrometry according to 2D-DIGE map. In identified proteins, there were 15 extracellular hydrolases secreted by A. niger including glucoamylase, acid protease, beta-glucanase, arabinofuranosidase, xylanase, and phytase. Some antioxidant related enzymes also were identified. These findings suggested that A. niger is able to secrete many extracellular degradation enzymes (especially lignocellulosic hydrolyzing enzymes, acid proteases and phytase) during fermentation of RSM, thus altering chemical composition and physicochemical properties of RSM.

Dataset Information

The carbon starvation response of Aspergillus niger during submerged cultivation: insights from the transcriptome and secretome.

Publications

The carbon starvation response of Aspergillus niger during submerged cultivation: insights from the transcriptome and secretome.

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