ABSTRACT
Mycelium networks are promising substrates for designing unconventional computing devices providing rich topologies and geometries where signals propagate and interact. Fulfilling our long-term objectives of prototyping electrical analog computers from living mycelium networks, including networks hybridised with nanoparticles, we explore the possibility of implementing Boolean logical gates based on electrical properties of fungal colonies. We converted a 3D image-data stack of Aspergillus niger fungal colony to an Euclidean graph and modelled the colony as resistive and capacitive (RC) networks, where electrical parameters of edges were functions of the edges' lengths. We found that and, or and and-not gates are implementable in RC networks derived from the geometrical structure of the real fungal colony.
Subject(s)
Aspergillus niger/physiology , Computer Simulation , Models, Biological , Mycelium/physiology , Spores, Fungal/physiology , Aspergillus niger/cytology , Colony Count, Microbial , Electric Stimulation , Microscopy, Confocal , Microscopy, FluorescenceABSTRACT
Some strains of Aspergillus niger have been previously reported to produce sclerotia under certain conditions. Sclerotia are aggregations of hyphae which can act either as survival or as sexual structures in species related to A. niger. In this study, we were able to induce the formation of sclerotia in the progenitor of the industrial citric acid producing strains of A. niger, ATCC 1015, and in pyrG mutants derived from it. Sclerotia can be stably formed by ATCC 1015 on malt extract agar medium supplemented with raisins, showing a spatial differentiation of the fungus dependent on the addition and on the position of the fruits into the medium. On other media, including malt extract agar, pyrG auxotrophs also form abundant sclerotia, while the complementation of this gene reverses this phenotype. Additionally, a macro- and microscopical analysis of the sclerotia is reported. Our results show that the sclerotia formed by A. niger are similar to those formed by other fungi, not only in their morphology but also in their ability to germinate and regenerate the organism.
Subject(s)
Aspergillus niger , Hyphae , Aspergillus niger/cytology , Aspergillus niger/genetics , Aspergillus niger/metabolism , Citric Acid/metabolism , Genes, Fungal/genetics , Hyphae/genetics , Hyphae/growth & development , Mutation , PhenotypeABSTRACT
Corn, sorghum and wheat grains are used as livestock feed in the world. Identification of black aspergilli associated with these grains is necessary to make sure of the safety of the grains because its occurrence is an indicator of mycotoxin production. Forty-five isolates were isolated from the samples collected from Upper Egypt's markets and identified morphologically based on colony color, conidia, stipe and vesicle size and molecularly by using ß-tubulin and calmodulin genes. Isolates were divided into 30 strains of Aspergillus welwitschiae and 15 strains of A. niger. We have found new criteria in the morphological identification of A. welwitschiae as its colony color was black to brown with yellow edge, but in A. niger was black with white edge, also A. welwitschiae sometimes produced finely-to-distinctly roughened brownish conidia on malt extract agar (MEA) media. Thirteen isolates of A. welwitschiae and six of A. niger were recognized as potential producers for ochratoxin A.
Subject(s)
Aspergillus niger/classification , Aspergillus niger/genetics , Aspergillus/classification , Aspergillus/genetics , Edible Grain/microbiology , Aspergillus/cytology , Aspergillus niger/cytology , Calmodulin/genetics , Mycological Typing Techniques , Ochratoxins , Sorghum/microbiology , Triticum/microbiology , Tubulin/genetics , Zea mays/microbiologyABSTRACT
In this paper, we present a mathematical model to describe filamentous fungal growth based on intracellular secretory vesicles (SVs), which transport cell wall components to the hyphal tip. Vesicular transport inside elongating hyphae is modeled as an advection-diffusion-reaction equation with a moving boundary, transformed into fixed coordinates, and discretized using a high-order weighted essentially nonoscillatory discretization scheme. The model describes the production and the consumption of SVs with kinetic functions. Simulations are subsequently compared against distributions of SVs visualized by enhanced green fluorescent protein in young Aspergillus niger hyphae after germination. Intensity profile data are obtained using an algorithm scripted in ImageJ that extracts mean intensity distributions from 3D time-lapse confocal measurement data. Simulated length growth is in good agreement with the experimental data. Our simulations further show that a decrease of effective vesicle transport velocity towards the tip can explain the observed tip accumulation of SVs.
Subject(s)
Aspergillus niger , Biological Transport/physiology , Secretory Vesicles/metabolism , Algorithms , Aspergillus niger/cytology , Aspergillus niger/metabolism , Green Fluorescent Proteins/analysis , Green Fluorescent Proteins/metabolism , Hyphae/metabolism , Image Processing, Computer-Assisted , Microscopy, Confocal , Models, BiologicalABSTRACT
The efficiency of current methods for industrial production of citric acid is limited. To achieve continuous citric acid production with enhanced yield and reduced cost, immobilized fermentation was employed in an Aspergillus niger 831 repeated fed-batch fermentation system. We developed a new type of material (PAF201), which was used as a carrier for the novel adsorption immobilization system. Hydrophobicity, pore size and concentration of carriers were researched in A. niger immobilization. The efficiency of the A. niger immobilization process was analyzed by scanning electron microscopy. Then eight-cycle repeated fed-batch cultures for citric acid production were carried out over 600â¯h, which showed stable production with maximum citric acid concentrations and productivity levels of 162.7â¯g/L and 2.26â¯gâ¯L-1â¯h-1, respectively. Compared with some other literatures about citric acid yield, PAF201 immobilization system is 11.3% higher than previous results. These results indicated that use of the new adsorption immobilization system could greatly improve citric acid productivity in repeated fed-batch fermentation. Moreover, these results could provide a guideline for A.niger or other filamentous fungi immobilization in industry.
Subject(s)
Aspergillus niger , Cells, Immobilized , Citric Acid , Aspergillus niger/cytology , Aspergillus niger/metabolism , Biofilms , Bioreactors/microbiology , Cells, Immobilized/cytology , Cells, Immobilized/metabolism , Citric Acid/analysis , Citric Acid/metabolism , Fermentation , PorosityABSTRACT
The enhancement of bioelectrochemical properties of microorganism by in situ formation of conducting polymer within the cell structures (e.g. cell wall) was performed. The synthesis of polypyrrole (Ppy) within fungi (Aspergillus niger) cells was achieved. Two different Aspergillus niger strains were selected due to their ability to produce glucose oxidase, which initiated the Ppy formation through products of enzymatic reaction. The evolution of Ppy structural features was investigated by absorption spectroscopy, cyclic voltammetry and Fourier transform infrared spectroscopy.
Subject(s)
Aspergillus niger/metabolism , Polymers/metabolism , Pyrroles/metabolism , Aspergillus niger/chemistry , Aspergillus niger/cytology , Biosynthetic Pathways , Electric Conductivity , Fungal Proteins/metabolism , Glucose Oxidase/metabolism , Polymerization , Polymers/analysis , Pyrroles/analysisABSTRACT
In the present work, a potent xylanase producing fungal strain Aspergillus niger (KP874102.1) was isolated through cultural and morphological observations from soil sample of Baramura forest, Tripura west, India. 28S rDNA technique was applied for genomic identification of this fungal strain. The isolated strain was found to be phylogenetically closely related to Aspergillus niger. Kinetic constants such as Km and Vmax for extracellular xylanase were determined using various substrate such as beech wood xylan, oat spelt xylan and CM cellulose through Lineweaver-Burk plot. Km, Vmax and Kcat for beech wood xylan are found to be 2.89mg/ml, 2442U and 426178Umlmg-1 respectively. Crude enzyme did not show also CM cellulose activity. The relative efficiency of oat spelt xylan was found to be 0.819 with respect to beech wood xylan. After acid hydrolysis, enzyme was able to produce reducing sugar with 17.7, 35.5, 50.8 and 65% (w/w) from orange peel after 15, 30, 45 and 60min incubation with cellulase free xylanase and maximum reducing sugar formation rate was found to be 55.96µg/ml/min. Therefore, the Aspergillus niger (KP874102.1) is considered as a potential candidate for enzymatic hydrolysis of orange peel.
Subject(s)
Aspergillus niger/cytology , Aspergillus niger/enzymology , Citrus sinensis/chemistry , Endo-1,4-beta Xylanases/isolation & purification , Endo-1,4-beta Xylanases/metabolism , Extracellular Space/enzymology , Hydrolysis , Industrial Waste , Kinetics , Substrate Specificity , Xylans/metabolismABSTRACT
Four strains of Aspergillus (Aspergillus niger CDBB-H-176, A. niger CDBB-H-175, A. niger ATCC 9642, and Aspergillus terreus CDBB-H-194) were used to produce extracellular ß-glucosidase. Using an orthogonal experimental design (L9), we optimized the parameters of culture medium to maximize the activity of ß-glucosidase. The optimal conditions (same for the four strains) were as follows: temperature, 30°C; pH, 6.0; orbital agitation, 200 rpm; concentration of sucrose, 0.5% (w/v). The most productive strain was A. niger CDBB-H-175, with a yield of 701.2 U/mL. In a second stage, we optimized (L18) the concentration of nutrients in the culture medium to determine whether this modification would increase the production of ß-glucosidase. The optimal conditions for A. niger CDBB-H-175 were as follows (%, w/v): NaNO3, 0.3; KCl, 0.3; KH2PO4, 0.15; NH4NO3, 0.1; NH4H2PO4, 0.1; MgSO4 · 7H2O, 0.05; yeast extract, 0.1. The production of ß-glucosidase under these conditions was 1207.9 U/mL. Enzymatic assays were used to characterize the enzyme; the optimum temperature and pH of ß-glucosidase produced by the four selected micro-organisms were found to be 65°C and 5.0, respectively. We determined the Michaelis-Menten constants (Km) only for A. niger CDBB-H-175 and CDBB-H-176; the values were 2.7 and 2.2 mM, respectively.
Subject(s)
Aspergillus niger/enzymology , Fermentation , Industrial Microbiology/methods , beta-Glucosidase/metabolism , Aspergillus niger/cytology , Aspergillus niger/metabolism , Culture Media/metabolism , Enzyme Stability , Hydrogen-Ion Concentration , TemperatureABSTRACT
The effects of electric current on membranes associated with metabolism modifications in Aspergillus brasiliensis (niger) ATCC 9642 were studied. A 450-mL electrochemical cell with titanium ruthenium-oxide coated electrodes and packed with 15g of perlite, as inert support, was inoculated with A. brasiliensis spores and incubated in a solid inert-substrate culture (12 d; 30°C). Then, 4.5days after starting the culture, a current of 0.42mAcm-2 was applied for 24h. The application of low-intensity electric current increased the molecular oxygen consumption rate in the mitochondrial respiratory chain, resulting in high concentrations of reactive oxygen species, promoting high lipoperoxidation levels, according to measured malondialdehyde, and consequent alterations in membrane permeability explained the high n-hexadecane (HXD) degradation rates observed here (4.7-fold higher than cultures without current). Finally, cell differentiation and spore production were strongly stimulated. The study contributes to the understanding of the effect of current on the cell membrane and its association with HXD metabolism.
Subject(s)
Aspergillus niger/cytology , Aspergillus niger/metabolism , Cell Membrane/metabolism , Electric Conductivity , Alkanes/metabolism , Biomass , Bioreactors/microbiology , Carbon Dioxide/metabolism , Electrochemistry , Oxygen/metabolism , Spores, Fungal/metabolismABSTRACT
The holocellulase from Aspergillus niger SH3 was characterized and found to contain 125 proteins including cellulases (26), hemicellulases (21), chitinases (10), esterases (6), amylases (4) and hypothetical protein (32). The crude enzyme was immobilized on five different nanoparticles (NPs) via physical adsorption and covalent coupling methods. The enzyme-nanoparticle complexes (ENC) were screened for protein binding, enzymatic activities and immobilization efficiency. Magnetic enzyme-nanoparticle complexes (MENC) showed higher immobilization efficiency (60-80%) for most of the enzymes. MENC also showed better catalytic efficiencies in term of higher Vmax and lower Km than free enzyme. Saccharification yields from alkali treated paddy straw were higher (375.39mg/gds) for covalently immobilized MENC than free enzyme (339.99mg/gds). The immobilized enzyme was used for two cycles of saccharification with 55% enzyme recovery. Hence, this study for the first time demonstrated the immobilization of indigenous enzyme and its utilization for saccharification of paddy straw.
Subject(s)
Cellulases/chemistry , Cellulases/metabolism , Enzymes, Immobilized/chemistry , Enzymes, Immobilized/metabolism , Ferric Compounds/chemistry , Nanoparticles/chemistry , Aspergillus niger/cytology , Aspergillus niger/enzymology , Carbohydrates/chemistry , Crops, Agricultural/chemistry , Extracellular Space/enzymology , Holoenzymes/chemistry , Holoenzymes/metabolism , Hydrogen-Ion Concentration , Hydrolysis , Kinetics , TemperatureABSTRACT
Filamentous fungi are widely used in industrial fermentation. Particular fungal morphology acts as a critical index for a successful fermentation. To break the bottleneck of morphological analysis, we have developed a reliable method for fungal morphological analysis. By this method, we can prepare hundreds of pellet samples simultaneously and obtain quantitative morphological information at large scale quickly. This method can largely increase the accuracy and reliability of morphological analysis result. Based on that, the studies of Aspergillus niger morphology under different oxygen supply conditions and shear rate conditions were carried out. As a result, the morphological responding patterns of A. niger morphology to these conditions were quantitatively demonstrated, which laid a solid foundation for the further scale-up.
Subject(s)
Aspergillus niger/cytology , Fermentation , Industrial Microbiology , Reproducibility of ResultsABSTRACT
UNLABELLED: Pores in fungal septa enable cytoplasmic streaming between hyphae and their compartments. Consequently, the mycelium can be considered unicellular. However, we show here that Woronin bodies close ~50% of the three most apical septa of growing hyphae of Aspergillus niger. The incidence of closure of the 9th and 10th septa was even ≥94%. Intercompartmental streaming of photoactivatable green fluorescent protein (PA-GFP) was not observed when the septa were closed, but open septa acted as a barrier, reducing the mobility rate of PA-GFP ~500 times. This mobility rate decreased with increasing septal age and under stress conditions, likely reflecting a regulatory mechanism affecting septal pore diameter. Modeling revealed that such regulation offers effective control of compound concentration between compartments. Modeling also showed that the incidence of septal closure in A. niger had an even stronger impact on cytoplasmic continuity. Cytoplasm of hyphal compartments was shown not to be in physical contact when separated by more than 4 septa. Together, data show that apical compartments of growing hyphae behave unicellularly, while older compartments have a multicellular organization. IMPORTANCE: The hyphae of higher fungi are compartmentalized by porous septa that enable cytosolic streaming. Therefore, it is believed that the mycelium shares cytoplasm. However, it is shown here that the septa of Aspergillus niger are always closed in the oldest part of the hyphae, and therefore, these compartments are physically isolated from each other. In contrast, only part of the septa is closed in the youngest part of the hyphae. Still, compartments in this hyphal part are physically isolated when separated by more than 4 septa. Even open septa act as a barrier for cytoplasmic mixing. The mobility rate through such septa reduces with increasing septal age and under stress conditions. Modeling shows that the septal pore width is set such that its regulation offers maximal control of compound concentration levels within the compartments. Together, we show for the first time that Aspergillus hyphae switch from a unicellular to multicellular organization.
Subject(s)
Aspergillus niger/cytology , Aspergillus niger/physiology , Hyphae/cytology , Hyphae/physiology , Aspergillus niger/growth & development , Aspergillus niger/metabolism , Genes, Reporter , Green Fluorescent Proteins/analysis , Green Fluorescent Proteins/genetics , Hyphae/growth & development , Hyphae/metabolismABSTRACT
Aspergillus species are highly abundant fungi worldwide. Their conidia are among the most dominant fungal spores in the air. Conidia are formed in chains on the vesicle of the asexual reproductive structure called the conidiophore. Here, it is shown that the velvet protein VeA of Aspergillus niger maximizes the diameter of the vesicle and the spore chain length. The length and width of the conidiophore stalk and vesicle were reduced nearly twofold in a ΔveA strain. The latter implies a fourfold reduced surface area to develop chains of spores. Over and above this, the conidial chain length was approximately fivefold reduced. The calculated 20-fold reduction in formation of conidia by ΔveA fits the 8- to 17-fold decrease in counted spore numbers. Notably, morphology of the ΔveA conidiophores of A. niger was very similar to that of wild-type Aspergillus sydowii. This suggests that VeA is key in conidiophore architecture diversity in the fungal kingdom. The finding that biomass formation of the A. niger ΔveA strain was reduced twofold shows that VeA not only impacts dispersion capacity but also colonization capacity of A. niger.
Subject(s)
Aspergillus niger/cytology , Aspergillus niger/growth & development , Fungal Proteins/metabolism , Spores, Fungal/cytology , Spores, Fungal/growth & development , Aspergillus niger/genetics , Biomass , Fungal Proteins/genetics , Gene Deletion , Spores, Fungal/geneticsABSTRACT
Aspergillus niger is a filamentous fungus that is extensively used in industrial fermentations for protein expression and the production of organic acids. Inherent biosynthetic capabilities, such as the capacity to secrete these biomolecules in high amounts, make A. niger an attractive production host. Although A. niger is renowned for this ability, the knowledge of the molecular components that underlie its production capacity, intercellular trafficking processes and secretion mechanisms is far from complete. Here, we introduce a standardized set of tools, consisting of an N-terminal GFP-actin fusion and codon optimized eforRed chromoprotein. Expression of the GFP-actin construct facilitates visualization of the actin filaments of the cytoskeleton, whereas expression of the chromoprotein construct results in a clearly distinguishable red phenotype. These experimentally validated constructs constitute the first set of standardized A. niger biomarkers, which can be used to study morphology, intercellular trafficking, and secretion phenomena.
Subject(s)
Aspergillus niger , Cellular Structures/ultrastructure , Organelles/ultrastructure , Actins/chemistry , Actins/metabolism , Aspergillus niger/chemistry , Aspergillus niger/cytology , Aspergillus niger/metabolism , Aspergillus niger/ultrastructure , Biomarkers/chemistry , Biomarkers/metabolism , Green Fluorescent Proteins/chemistry , Green Fluorescent Proteins/metabolism , Single-Cell AnalysisABSTRACT
In the tricarboxylic acid (TCA) cycle, NADP(+)-specific isocitrate dehydrogenase (NADP(+)-ICDH) catalyzes oxidative decarboxylation of isocitric acid to form α-ketoglutaric acid with NADP(+) as a cofactor. We constructed an NADP(+)-ICDH gene (icdA)-overexpressing strain (OPI-1) using Aspergillus niger WU-2223L as a host and examined the effects of increase in NADP(+)-ICDH activity on citric acid production. Under citric acid-producing conditions with glucose as the carbon source, the amounts of citric acid produced and glucose consumed by OPI-1 for the 12-d cultivation period decreased by 18.7 and 10.5%, respectively, compared with those by WU-2223L. These results indicate that the amount of citric acid produced by A. niger can be altered with the NADP(+)-ICDH activity. Therefore, NADP(+)-ICDH is an important regulator of citric acid production in the TCA cycle of A. niger. Thus, we propose that the icdA gene is a potentially valuable tool for modulating citric acid production by metabolic engineering.
Subject(s)
Aspergillus niger/genetics , Aspergillus niger/metabolism , Citric Acid/metabolism , Isocitrate Dehydrogenase/genetics , Aspergillus niger/cytology , Gene Expression , Intracellular Space/metabolism , Malates/metabolism , Metabolic EngineeringABSTRACT
Several species in Aspergillus section Nigri have been reported to produce sclerotia on well-known growth media, such as Czapek yeast autolysate (CYA) agar, with sclerotia considered to be an important prerequisite for sexual development. However Aspergillus niger sensu stricto has not been reported to produce sclerotia, and is thought to be a purely asexual organism. Here we report, for the first time, the production of sclerotia by certain strains of Aspergillus niger when grown on CYA agar with raisins, or on other fruits or on rice. Up to 11 apolar indoloterpenes of the aflavinine type were detected by liquid chromatography and diode array and mass spectrometric detection where sclerotia were formed, including 10,23-dihydro-24,25-dehydroaflavinine. Sclerotium induction can thus be a way of inducing the production of new secondary metabolites from previously silent gene clusters. Cultivation of other species of the black aspergilli showed that raisins induced sclerotium formation by A. brasiliensis, A. floridensis A. ibericus, A. luchuensis, A. neoniger, A. trinidadensis and A. saccharolyticus for the first time.
Subject(s)
Aspergillus niger/metabolism , Terpenes/chemistry , Terpenes/metabolism , Aspergillus niger/cytology , Aspergillus niger/genetics , Multigene Family , Mutation , Mycelium/metabolism , Species SpecificityABSTRACT
Production and optimization of ß-N-acetyl glucosaminidase and chitinase by Ca-alginate immobilized Aeromonas hydrophila SBK1 was carried out using prawn shell as cost-effective substrate. Beads prepared with 5.0% Na-alginate (containing 2.0% colloidal chitin) and 1.0 M CaCl2 showed considerable beads integrity and supported maximum production of chitinolytic enzymes. Bead diameter, 3 mm; temperature, 35°C; pH 7.0; agitation, 90 rpm were found ideal for the maximum production of the enzymes. The fermentation and thermodynamic indices revealed the feasibility of immobilized cells over free cells for enzymes production. Reasonable amount of chitosaccharides (degree of polymerization; 1-6) accumulated in the production media which have paramount antioxidant activity. Scale up experiment was successfully carried out in 5 L fermentor. In immobilized state, the chitosaccharides yield and antioxidant activity increased about 44.76% and 22.22%, whereas specific productivity of ß-N-acetyl glucosaminidase and chitinase increased by 22.86% and 33.37% over free state. The cell entrapped beads can be reused upto ten cycles without marked loss of its biocatalytic efficiency. High level of protoplast of Aspergillus niger was generated by treating mycelia with 10 U/ml of crude chitinase after 4 h at pH 7.0 and in the temperature 35-40°C, and 67% of the protoplasts were found to be regenerated.
Subject(s)
Aeromonas hydrophila/metabolism , Animal Shells/metabolism , Aspergillus niger/cytology , Chitinases/biosynthesis , Chitinases/metabolism , Protoplasts/metabolism , Acetylglucosaminidase/biosynthesis , Acetylglucosaminidase/metabolism , Alginates/metabolism , Alginates/pharmacology , Animal Shells/chemistry , Animals , Bioreactors , Calcium Chloride/metabolism , Calcium Chloride/pharmacology , Cells, Immobilized/metabolism , Chitin/metabolism , Fermentation , Glucuronic Acid/metabolism , Glucuronic Acid/pharmacology , Hexuronic Acids/metabolism , Hexuronic Acids/pharmacology , Hydrogen-Ion Concentration , Hydrolysis , Kinetics , Particle Size , Penaeidae , TemperatureABSTRACT
RacA is the main Rho GTPase in Aspergillus niger regulating polarity maintenance via controlling actin dynamics. Both deletion and dominant activation of RacA (Rac(G18V)) provoke an actin localization defect and thereby loss of polarized tip extension, resulting in frequent dichotomous branching in the ΔracA strain and an apolar growing phenotype for Rac(G18V). In the current study the transcriptomics and physiological consequences of these morphological changes were investigated and compared with the data of the morphogenetic network model for the dichotomous branching mutant ramosa-1. This integrated approach revealed that polar tip growth is most likely orchestrated by the concerted activities of phospholipid signaling, sphingolipid signaling, TORC2 signaling, calcium signaling and CWI signaling pathways. The transcriptomic signatures and the reconstructed network model for all three morphology mutants (ΔracA, Rac(G18V), ramosa-1) imply that these pathways become integrated to bring about different physiological adaptations including changes in sterol, zinc and amino acid metabolism and changes in ion transport and protein trafficking. Finally, the fate of exocytotic (SncA) and endocytotic (AbpA, SlaB) markers in the dichotomous branching mutant ΔracA was followed, demonstrating that hyperbranching does not per se result in increased protein secretion.
Subject(s)
Aspergillus niger/cytology , Aspergillus niger/genetics , Fungal Proteins/genetics , Morphogenesis/physiology , Transcriptome/genetics , Morphogenesis/genetics , Signal Transduction/genetics , Signal Transduction/physiologyABSTRACT
Autophagy is a well-conserved catabolic process constitutively active in eukaryotes that is involved in maintaining cellular homeostasis by the targeting of cytoplasmic content and organelles to vacuoles. Autophagy is strongly induced by the limitation of nutrients including carbon, nitrogen, and oxygen and is clearly associated with cell death. It has been demonstrated that the accumulation of empty hyphal compartments and cryptic growth in carbon-starved submerged cultures of the filamentous fungus Aspergillus niger is accompanied by a joint transcriptional induction of autophagy genes. This study examines the role of autophagy by deleting the atg1, atg8, and atg17 orthologs in A. niger and phenotypically analyzing the deletion mutants in surface and submerged cultures. The results indicate that atg1 and atg8 are essential for efficient autophagy, whereas deletion of atg17 has little to no effect on autophagy in A. niger. Depending on the kind of oxidative stress confronted with, autophagy deficiency renders A. niger either more resistant (menadione) or more sensitive (H2O2) to oxidative stress. Fluorescence microscopy showed that mitochondrial turnover upon carbon depletion in submerged cultures is severely blocked in autophagy-impaired A. niger mutants. Furthermore, automated image analysis demonstrated that autophagy promotes survival in maintained carbon-starved cultures of A. niger. Taken together, the results suggest that besides its function in nutrient recycling, autophagy plays important roles in physiological adaptation by organelle turnover and protection against cell death upon carbon depletion in submerged cultures.
Subject(s)
Aspergillus niger/cytology , Aspergillus niger/growth & development , Autophagy , Aspergillus niger/metabolism , Carbon/metabolism , Culture Media/metabolism , Fungal Proteins/genetics , Fungal Proteins/metabolism , Hydrogen Peroxide/metabolism , Hyphae/cytology , Hyphae/growth & development , Hyphae/metabolism , Microbial Viability , Nitrogen/metabolism , Oxidative StressABSTRACT
The filamentous fungus Aspergillus niger is a widely used host in industrial processes from food, chemical to pharmaceutical industry. The most prominent feature of this filamentous microorganism in submerged cultivation is its complex morphology which comprises dense spherical pellets as well as viscous elongated filaments. Depending on culture conditions, the exhibited morphology has tremendous effect on the overall process, making a precise understanding of fungal growth and morphology indispensable. Morphology, however, is only industrially relevant as long as it can be linked to important cultivation characteristics of filamentous microorganisms such as culture broth flow behavior. In the present study, different conventional and fractal morphological parameters gained from automatic image analysis were tested for their eligibility to predict culture broth rheology from morphologic appearance. The introduced biomass independent rheological parameters K(BDW) and n(BDW) obtained by power law relationship were successfully estimated from morphology related fractal and conventional parameters. For improved characterization of morphologic appearance of filamentous fungi newly introduced fractal quotient and lacunarity were compared to conventional particle shape parameters in form of the earlier established Morphology number (MN).