► New bioprocesses for the production of cellulolytic enzymes are needed. ► A novel combined cultivation method for cellulase production is being proposed. ► The new method resulted in a 3-fold ...improvement over conventional fermentation.
Sequential solid-state and submerged cultivation with sugarcane bagasse as substrate for cellulase production by Aspergillus niger A12 was assessed by measuring endoglucanase activity. An unconventional pre-culture with an initial fungal growth phase under solid-state cultivation was followed by a transition to submerged fermentation by adding the liquid culture medium to the mycelium grown on solid substrate. For comparison, control experiments were conducted using conventional submerged cultivation. The cultures were carried out in shake flasks and in a 5-L bubble column bioreactor. An endoglucanase productivity of 57±13IU/L/h was achieved in bubble column cultivations prepared using the new method, representing an approximately 3-fold improvement compared to conventional submerged fermentation. Therefore, the methodology proposed here of a sequential fermentation process offers a promising alternative for cellulase production.
The veA gene is a key regulator governing morphogenetic development and secondary metabolism in many fungi. Here, we characterized and disrupted a veA orthologue in an ochratoxigenic Aspergillus ...niger strain. Morphological development, ochratoxin A (OTA) biosynthesis, and oxidative stress tolerance in the wild-type and veA disruption strains were further analyzed. Accordingly, the link between the veA gene and development of specific gene brlA, OTA biosynthesis key gene pks, and oxidative-stress-tolerance-related gene cat was explored. Results demonstrated that the veA gene acts as a positive regulator of conidia production, OTA biosynthesis, and oxidative stress tolerance in A. niger, regardless of light conditions. Darkness promoted conidial production and OTA biosynthesis in the A. niger wild-type strain. Our results contribute to a better understanding of the veA regulatory mechanism and suggest the veA gene as a potential target for developing control strategies for A. niger infection and OTA biosynthesis.
•Dynamic high pressure homogenization a simple method to obtain chitin nanofibers.•The obtained chitin nanofibers presented uniform width and high aspect ratio.•Nano nature of chitin nanofibers plays ...an important role in antifungal activity.•Chitin nanofibers shape contributes to a major breakthrough in chitin applications.
Chitin nano-objects become more interesting and attractive material than native chitin because of their usable form, low density, high surface area and promising mechanical properties. This work suggests a straightforward and environmentally friendly method for processing chitin nanofibers using dynamic high pressure homogenization. This technique proved to be a remarkably simple way to get α-chitin into α-chitin nanofibers from yellow lobster wastes with a uniform width (bellow 100nm) and high aspect ratio; and may contributes to a major breakthrough in chitin applications. Moreover, the resulting α-chitin nanofibers were characterized and compared with native α-chitin in terms of chemical and crystal structure, thermal degradation and antifungal activity. The biological assays highlighted that the nano nature of chitin nanofibers plays an important role in the antifungal activity against Aspergillus niger.
Aspergillus niger α
-glucosidase (ANG), a member of glycoside hydrolase family 31, catalyzes hydrolysis of
α
-glucosidic linkages at the non-reducing end. In the presence of high concentrations of ...maltose, the enzyme also catalyzes the formation of
α
-(1→6)-glucosyl products by transglucosylation and it is used for production of the industrially useful panose and isomaltooligosaccharides. The initial transglucosylation by wild-type ANG in the presence of 100 mM maltose Glc(
α
1–4)Glc yields both
α
-(1→6)- and
α
-(1→4)-glucosidic linkages, the latter constituting ~25% of the total transfer reaction product. The maltotriose Glc(
α
1–4)Glc(
α
1–4)Glc,
α
-(1→4)-glucosyl product disappears quickly, whereas the
α
-(1→6)-glucosyl products panose Glc(
α
1–6)Glc(
α
1–4)Glc, isomaltose Glc(
α
1–6)Glc, and isomaltotriose Glc(
α
1–6)Glc(
α
1–6)Glc accumulate. To modify the transglucosylation properties of ANG, residue Asn694, which was predicted to be involved in formation of the plus subsites of ANG, was replaced with Ala, Leu, Phe, and Trp. Except for N694A, the mutations enhanced the initial velocity of the
α
-(1→4)-transfer reaction to produce maltotriose, which was then degraded at a rate similar to that by wild-type ANG. With increasing reaction time, N694F and N694W mutations led to the accumulation of larger amounts of isomaltose and isomaltotriose than achieved with the wild-type enzyme. In the final stage of the reaction, the major product was panose (N694A and N694L) or isomaltose (N694F and N694W).
Summary
In this study, the ability of the geoactive fungus Aspergillus niger to colonize and transform manganese nodules from the Clarion‐Clipperton Zone in both solid and liquid media was ...investigated. Aspergillus niger was able to colonize and penetrate manganese nodules embedded in solid medium and effect extensive transformation of the mineral in both fragmented and powder forms, precipitating manganese and calcium oxalates. Transformation of manganese nodule powder also occurred in a liquid medium in which A. niger was able to remove the fine particles from suspension which were accumulated within the central region of the resulting mycelial pellets and transformed into manganese oxalate dihydrate (lindbergite) and calcium oxalate dihydrate (weddellite). These findings contribute to an understanding of environmental processes involving insoluble manganese oxides, with practical relevance to chemoorganotrophic mineral bioprocessing applications, and, to the best of our knowledge, represent the first demonstration of fundamental direct and indirect interactions between geoactive fungi and manganese nodules.
In this study, a novel fungus FAD dependent glucose dehydrogenase, derived from Aspergillus niger (AnGDH), was characterized. This enzyme's potential for the use as the enzyme for blood glucose ...monitor enzyme sensor strips was evaluated, especially by investigating the effect of the presence of xylose during glucose measurements. The substrate specificity of AnGDH towards glucose was investigated, and only xylose was found as a competing substrate. The specific catalytic efficiency for xylose compared to glucose was 1.8%. The specific activity of AnGDH for xylose at 5mM concentration compared to glucose was 3.5%. No other sugars were used as substrate by this enzyme. The superior substrate specificity of AnGDH was also demonstrated in the performance of enzyme sensor strips. The impact of spiking xylose in a sample with physiological glucose concentrations on the sensor signals was investigated, and it was found that enzyme sensor strips using AnGDH were not affected at all by 5mM (75mg/dL) xylose. This is the first report of an enzyme sensor strip using a fungus derived FADGDH, which did not show any positive bias at a therapeutic level xylose concentration on the signal for a glucose sample. This clearly indicates the superiority of AnGDH over other conventionally used fungi derived FADGDHs in the application for SMBG sensor strips. The negligible activity of AnGDH towards xylose was also explained on the basis of a 3D structural model, which was compared to the 3D structures of A. flavus derived FADGDH and of two glucose oxidases.
•Novel fungus FAD dependent glucose dehydrogenase (AnGDH) from Aspergillus niger.•High catalytic efficiency and high glucose specificity.•Activity observed only with glucose and xylose as substrate.•Specific catalytic efficiency towards xylose was 1.8% of that towards glucose.•Enzyme sensor response to physiological glucose not affected by therapeutic xylose.
A characteristic hallmark of
Aspergillus niger is the formation of black conidiospores. We have identified four loci involved in spore pigmentation of
A. niger by using a combined genomic and ...classical complementation approach
. First, we characterized a newly isolated color mutant,
colA, which lacked pigmentation resulting in white or colorless conidia. Pigmentation of the
colA mutant was restored by a gene (An12g03950) which encodes a putative 4′phosphopantetheinyl transferase protein (PptA). 4′Phosphopantetheinyl transferase activity is required for the activation of Polyketide Synthases (PKSs) and/or Non-Ribosomal Peptide Synthases (NRPSs). The loci whose mutation resulted in fawn, olive, and brown color phenotypes were identified by complementation. The fawn phenotype was complemented by a PKS protein (FwnA, An09g05730), the
ovlA mutant by An14g05350 (OlvA) and the
brnA mutant by An14g05370 (BrnA), the respective homologs of
alb1/pksP,
ayg1 and
abr1 in
A. fumigatus. Targeted disruption of the
pptA,
fwnA,
olvA and
brnA genes confirmed the complementation results. Disruption of the
pptA gene abolished synthesis of all polyketides and non-ribosomal peptides, while the naphtho-γ-pyrone subclass of polyketides were specifically dependent on
fwnA, and funalenone on
fwnA, olvA and
brnA. Thus, secondary metabolite profiling of the color mutants revealed a close relationship between polyketide synthesis and conidial pigmentation in
A. niger.
Summary
Interaction between microbes affects the growth, metabolism and differentiation of members of the microbial community. While direct and indirect competition, like antagonism and nutrient ...consumption have a negative effect on the interacting members of the population, microbes have also evolved in nature not only to fight, but in some cases to adapt to or support each other, while increasing the fitness of the community. The presence of bacteria and fungi in soil results in various interactions including mutualism. Bacilli attach to the plant root and form complex communities in the rhizosphere. Bacillus subtilis, when grown in the presence of Aspergillus niger, interacts similarly with the fungus, by attaching and growing on the hyphae. Based on data obtained in a dual transcriptome experiment, we suggest that both fungi and bacteria alter their metabolism during this interaction. Interestingly, the transcription of genes related to the antifungal and putative antibacterial defence mechanism of B. subtilis and A. niger, respectively, are decreased upon attachment of bacteria to the mycelia. Analysis of the culture supernatant suggests that surfactin production by B. subtilis was reduced when the bacterium was co‐cultivated with the fungus. Our experiments provide new insights into the interaction between a bacterium and a fungus.
The polyketide synthase gene An15g07920 was known in Aspergillus niger CBS 513.88 as putatively involved in the production of ochratoxin A (OTA). Genome resequencing analysis revealed that the gene ...An15g07920 is also present in the ochratoxin-producing A. niger strain 1062. Disruption of An15g07920 in A. niger 1062 removed its capacity to biosynthesize ochratoxin β (OTβ), ochratoxin α (OTα), and OTA. These results indicate that the polyketide synthase encoded by An15g07920 is a crucial player in the biosynthesis of OTA, in the pathway prior to the phenylalanine ligation step. The gene An15g07920 reached its maximum transcription level before OTA accumulation reached its highest level, confirming that gene transcription precedes OTA production. These findings will not only help explain the mechanism of OTA production in A. niger but also provide necessary information for the development of effective diagnostic, preventive, and control strategies to reduce the risk of OTA contamination in foods.
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