The Effect of Some Sugars on the Growth of Aspergillus niger (original) (raw)
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Journal of Fungi
Fungi play a critical role in the global carbon cycle by degrading plant polysaccharides to small sugars and metabolizing them as carbon and energy sources. We mapped the well-established sugar metabolic network of Aspergillus niger to five taxonomically distant species (Aspergillus nidulans, Penicillium subrubescens, Trichoderma reesei, Phanerochaete chrysosporium and Dichomitus squalens) using an orthology-based approach. The diversity of sugar metabolism correlates well with the taxonomic distance of the fungi. The pathways are highly conserved between the three studied Eurotiomycetes (A. niger, A. nidulans, P. subrubescens). A higher level of diversity was observed between the T. reesei and A. niger, and even more so for the two Basidiomycetes. These results were confirmed by integrative analysis of transcriptome, proteome and metabolome, as well as growth profiles of the fungi growing on the corresponding sugars. In conclusion, the establishment of sugar pathway models in diffe...
Scientific Reports
In nature, the fungus Aspergillus niger degrades plant biomass polysaccharides to monomeric sugars, transports them into its cells, and uses catabolic pathways to convert them into biochemical building blocks and energy. We show that when grown in liquid cultures, A. niger takes up plant-biomass derived sugars in a largely sequential manner. Interestingly, this sequential uptake was not mediated by the fungal general carbon catabolite repressor protein CreA. Furthermore, transcriptome analysis strongly indicated that the preferential use of the monomeric sugars is arranged at the level of transport, but it is not reflected in transcriptional regulation of sugar catabolism. Therefore, the results indicate that the regulation of sugar transport and catabolism are separate processes in A. niger. Plant biomass is a complex entity containing both structural and storage polymers that consist of several sugar monomers. Aspergillus niger is a ubiquitous filamentous ascomycete fungus, which efficiently degrades all plant polysaccharides through a wide range of extracellular carbohydrate acting enzymes (CAZymes) 1. The resulting sugars are taken up by the fungal cell and converted to energy or biomolecule precursors through a variety of metabolic pathways 2. A. niger is also one of the main industrial producers of enzymes for the conversion of plant-based feedstocks to fermentable sugars 3. Although nowadays more complex substrates are used as a carbon and energy source in fungal fermentations, growth on monomeric sugars is utmost important to understand the physiology of the fungus. A fine-tuned regulatory mechanism enables A. niger to utilize the available carbon source in the physiologically most beneficial manner. During growth in natural biotopes, fungi are confronted with a heterogeneous mixture of carbon sources of which, due to substrate consumption that supports fungal growth, the composition changes over time. For fungi to thrive and propagate, it is essential that the set of expressed genes enables utilization of the energetically most optimal carbon source, and adapts in response to changes in the substrate composition. The expression of the genes required for the extracellular degradation of the polysaccharides and the subsequent intracellular metabolic conversion of the sugar residues is therefore controlled by a set of transcriptional activators and repressors that respond to specific inducers 4. Carbon catabolite repression, mediated by CreA, ensures that the presence of a preferred carbon source (e.g. glucose) prevents expression of genes involved in utilization of less-preferred carbon sources 5. CreA has been hypothesized to be the key mechanism in fungi to ensure the optimal match to available substrate, as increasing free sugar concentrations in fungal habitats increase repression of genes encoding polysaccharide-degrading enzymes 4. To achieve carbon repression through CreA, high transcript levels of creA are required, as well as glucose transport and at least partially the presence of CreB 6. CreB is part of the CreC-CreB deubiquitination complex that is essential for CreA function and stability 7. Deletion of CreA can result in upregulation of many genes, but also in a more clear distinction between the sugars that induce expression of different sets of plant biomass degradation related genes, such as has been shown for a set of pectinolytic genes in A. niger 8 .
d���Galactose uptake is nonfunctional in the conidiospores of Aspergillus niger
2012
The majority of black Aspergilli (Aspergillus section Nigri), including Aspergillus niger, as well as many other Ascomycetes fail to germinate on D-galactose as a sole carbon source. Here, we provide evidence that the ability of A. niger to transport D-galactose is growth stage dependent, being absent in the conidiospores but present in the mycelia. Despite earlier claims, we could identify galactokinase activity in growing cells and all genes of the Leloir pathway (responsible for channelling D-galactose into the EMP pathway) are well induced on D-galactose (and also on lactose, D-xylose and L-arabinose) in the mycelial stage. Expression of all Leloir pathway genes was also detectable in conidiospores, although galE (encoding a galactokinase) and galD (encoding a galactose-1-phosphate uridylyl transferase) were expressed poorly. These results suggest that the D-galactose-negative phenotype of A. niger conidiospores may be due to the lack of inducer uptake.
Production and action of an Aspergillus phoenicis enzymatic pool using different carbon sources
Brazilian Journal of Food Technology, 2012
Aspergillus phoenicis is an interesting heat tolerant fungus that can synthesize enzymes with several applications in the food industry due to its great hydrolytic potential. In this work, the fungus produced high enzymatic levels when cultivated on inexpensive culture media consisting of flakes from different origins such as cassava flour, wheat fibre, crushed soybean, agro-industrial wastes, starch, glucose or maltose. Several enzymatic systems were produced from these carbon sources, but amylase was the most evident, followed by pectinase and xylanase. Traces of CMCases, avicelase, lipase, β-xylosidase, β-glucosidase and α-glucosidase activities were also detected. Amylases were produced on rye flakes, starch, oat flakes, corn flakes, cassava flour and wheat fibre. Significant amylolytic levels were produced in the culture medium with glucose or when this sugar was exhausted, suggesting an enzyme in the constitutive form. Cassava flour, rye, oats, barley and corn flakes were also used as substrates in the hydrolytic reactions, aiming to verify the liberation potential of reducing sugars. Corn flakes induced greater liberation of reducing sugars as compared to the others. Thin layer chromatography of the reaction end products showed that the hydrolysis of cassava flour liberated maltooligosaccharides, but cassava flour and corn, rye, oats and barley flakes were hydrolyzed to glucose. These results suggested the presence of glucoamylase and α-amylase as part of the enzymatic pool of A. phoencis.
Applied Biochemistry and Biotechnology, 1999
The effect of culture conditions such as medium composition and shear stress on the fungal pellet morphology in shake-flask cultures and its relation to glucose oxidase (GOD) excretion by recombinant Aspergillus niger NRRL 3 (GOD 3–18) was investigated. It was shown that culture conditions resulting in the formation of smaller fungal pellets with an increased mycelial density result in higher yields of exocellular GOD. The pellets obtained in shake-flask cultures showed distinct layers of mycelial density with only the thin outer layer consisting of a dense mycelial network. The performance of the recombinant strain and the process of pellet formation was also analyzed during batch cultivation in a stirred-tank bioreactor. It was shown that the process of pellet formation occurred in two steps: (1) aggregation of free spores to spore clusters with subsequent germination and formation of small aggregates surrounded by a loose hyphal network, and (2) aggregation of the primary aggregates to the final full-size pellets. The fungal pellets formed during bioreactor cultivation were smaller, did not show large differences in mycelial density, and were more efficient with respect to the production of exocellular GOD. The decreasing pellet size also correlated with an increased mycelial density, indicating an improvement of the transport of nutrients to the inner parts of the pellet.
Process Biochemistry, 2004
The kinetics of substrate uptake and product formation in the process of citric acid accumulation by Aspergillus niger on sucrose as a sole carbon source are presented. The experiments are aimed at studying if glucose and fructose obtained from the hydrolysis of sucrose are equivalent carbon sources for A. niger and how the presence of the two different carbon substrates might influence the citric acid formation process. Beet sugar was used as a sole carbon source in the first series of experiments conducted in two types of bioreactors: stirred tank and air-lift. The fructose uptake rate was significantly lower than the glucose uptake rate in the late idiophase. A substrate utilisation breakpoint occurred when a large amount of citric acid was accumulated in the fermentation broth. A similar phenomenon was also detected in repeated fed-batch fermentation. This phenomenon was confirmed by the second series of parallel shake culture runs, in which fungal growth and citric acid accumulation by A. niger was simultaneously tested on the media containing the following carbon sources: sucrose, glucose and fructose, with and without addition of concentrated citric acid solution. Finally, it was shown that high concentration of citric acid strongly depleted fructose uptake rate.
Advances in Microbiology, 2014
A mesophilic strain of Aspergillus niger isolated from cassava effluent samples produced extracellular glucoamylase in submerged culture containing 2% (w/v) soluble or sweet potato starch. On soluble starch medium the maximum glucoamylase activity in the culture filtrate was 9.40 U/mg compared to 8.24 U/mg on sweet potato starch culture filtrate. The mycelial dry weight for both media was 494 and 418 mg respectively. The maximum glucoamylase activity was obtained at a growth temperature of 40˚C and pH 4.5. The implication is that the bioprocess of utilizing sweet potato starch in the culture is attractive due to its relatively cheaper availability in Nigeria, making it even more favorable when economics is considered.
Fungal Genetics and Biology, 2014
Fungi are an important source of enzymes for saccharification of plant polysaccharides and production of biofuels. Understanding of the regulation and induction of expression of genes encoding these enzymes is still incomplete. To explore the induction mechanism, we analysed the response of the industrially important fungus Aspergillus niger to wheat straw, with a focus on events occurring shortly after exposure to the substrate. RNA sequencing showed that the transcriptional response after 6 h of exposure to wheat straw was very different from the response at 24 h of exposure to the same substrate. For example, less than half of the genes encoding carbohydrate active enzymes that were induced after 24 h of exposure to wheat straw, were also induced after 6 h exposure. Importantly, over a third of the genes induced after 6 h of exposure to wheat straw were also induced during 6 h of carbon starvation, indicating that carbon starvation is probably an important factor in the early response to wheat straw. The up-regulation of the expression of a high number of genes encoding CAZymes that are active on plant-derived carbohydrates during early carbon starvation suggests that these enzymes could be involved in a scouting role during starvation, releasing inducing sugars from complex plant polysaccharides. We show, using proteomics, that carbon-starved cultures indeed release CAZymes with predicted activity on plant polysaccharides. Analysis of the enzymatic activity and the reaction products, indicates that these proteins are enzymes that can degrade various plant polysaccharides to generate both known, as well as potentially new, inducers of CAZymes.
The Effect of Carbon Source of Growth on α-Amylase Production by Aspergillus flavus
2015
Background: Aspergillus flavus is known for its capability of production of aflatoxins in food grains in the tropics. It was also recently demonstrated as capable of production of α-amylase in a defined medium with potassium nitrate and some other nitrogen compounds as nitrogen source for fungal growth and development (Adejuwon et al., 2015, Advances in Bioscience and Bioengineering). Materials and methods: In this current investigation a same defined growth medium with potassium nitrate as nitrogen source was inoculated with spore suspensions of approximately 7x105 spores per ml of Aspergillus flavus. The carbon source for growth was varied and was independently bread, starch, maltose, sucrose, lactose, glucose and galactose. Incubation was at 30oC. Extracellular proteins produced in medium was monitored daily and analysed for α-amylase activity. Results: The proteins produced by Aspergillus flavus in the inoculated medium exhibited α-amylase activity. All the carbon compounds ...