The Aspergillus niger faeB gene encodes a second feruloyl esterase involved in pectin and xylan degradation and is specifically induced in the presence of aromatic compounds

The faeB gene encoding a second feruloyl esterase from Aspergillus niger has been cloned and characterized. It consists of an open reading frame of 1644 bp containing one intron. The gene encodes a protein of 521 amino acids that has sequence similarity to that of an Aspergillus oryzae tannase. However, the encoded enzyme, feruloyl esterase B (FAEB), does not have tannase activity. Comparison of the physical characteristics and substrate specificity of FAEB with those of a cinnamoyl esterase from A. niger [Kroon, Faulds and Williamson (1996) Biotechnol. Appl. Biochem. 23, 255-262] suggests that they are in fact the same enzyme. The expression of faeB is specifically induced in the presence of certain aromatic compounds, but not in the presence of other constituents present in plant-cell-wall polysaccharides such as arabinoxylan or pectin. The expression profile of faeB in the presence of aromatic compounds was compared with the expression of A. niger faeA, encoding feruloyl esterase A (FAEA), and A. niger bphA, the gene encoding a benzoate-p-hydroxylase. All three genes have different subsets of aromatic compounds that induce their expression, indicating the presence of different transcription activating systems in A. niger that respond to aromatic compounds. Comparison of the activity of FAEA and FAEB on sugar-beet pectin and wheat arabinoxylan demonstrated that they are both involved in the degradation of both polysaccharides, but have opposite preferences for these substrates. FAEA is more active than FAEB towards wheat arabinoxylan, whereas FAEB is more active than FAEA towards sugar-beet pectin

Regulation of pentose catabolic pathway genes of Aspergillus niger

The aim of this study was to obtain a better understanding of the pentose catabolism in Aspergillus niger and the regulatory systems that affect it. To this end, we have cloned and characterised the genes encoding A. niger L-arabitol dehydrogenase (ladA) and xylitol dehydrogenase (xdhA), and compared the regulation of these genes to other genes of the pentose catabolic pathway. This demonstrated that activation of the pathway depends on two transcriptional regulators, the xylanolytic activator (XlnR) and an unidentified L-arabinose specific regulator (AraR). These two regulators affect those genes of the pentose catabolic pathway that are related to catabolic conversion of their corresponding inducers (D-xylose and L-arabinose, respectively)

Glucose uptake and growth of glucose-limited chemostat cultures of Aspergillus niger and a disruptant lacking MstA, a high-affinity glucose transporter

This is a study of high-affinity glucose uptake in Aspergillus niger and the effect of disruption of a high-affinity monosaccharide-transporter gene, mstA. The substrate saturation constant (K-s) of a reference strain was about 15 mu M in glucose-limited chemostat culture. Disruption of mstA resulted in a two- to fivefold reduction in affinity for glucose and led to expression of a low-affinity glucose transport gene, mstC, at high dilution rate. The effect of mstA disruption was more subtle at low and intermediate dilution rates, pointing to some degree of functional redundancy in the high-affinity uptake system of A. niger. The mstA disruptant and a reference strain were cultivated in glucose-limited chemostat cultures at low, intermediate and high dilution rate (D=0.07 h(-1), 0.14 h(-1) and 0.20 h(-1)). Mycelium harvested from steady-state cultures was subjected to glucose uptake assays, and analysed for expression of mstA and two other transporter genes, mstC and mstF The capacity for glucose uptake (V-max) of both strains was significantly reduced at low dilution rate. The glucose uptake assays revealed complex uptake kinetics. This impeded accurate determination of maximum specific uptake rates (V-max) and apparent affinity constants (K-m(app)) at intermediate and high dilution rate. Two high-affinity glucose transporter genes, mstA and mstF, were expressed at all three dilution rates in chemostat cultures, in contrast to batch culture, where only mstC was expressed. Expression patterns of the three transporter genes suggested differential regulation and functionality of their products

Expression of agsA, one of five 1,3-alpha-D-glucan synthease-encoding genes in Aspergillus niger, is induced in response to cell wall stress.

1,3-alpha-D-Glucan is an important component of the cell wall of filamentous fungi. We have identified a family of five 1,3-alpha-D-glucan synthase-encoding genes in Aspergillus niger. The agsA gene was sequenced and the predicted protein sequence indicated that the overall domain structure of 1,3-alpha-D-glucan synthases is conserved in fungi. Using RT-PCR and Northern blot analysis, we found that expression of the agsA gene and to a lesser extent also of agsE were induced in the presence of the cell wall stress-inducing compounds such as Calcofluor White (CFW), SDS, and caspofungin. Loss of agsA function did not result in an apparent phenotype under normal growth conditions but rendered the cells more sensitive to CFW. The induction of 1,3-alpha-D-glucan synthase-encoding genes in response to cell wall stress was not limited to A. niger, but was also observed in Penicillium chrysogenum. We propose that this response to cell wall stress commonly occurs in filamentous fungi

Aspergillus cibarius sp. nov., from traditional meju in Korea

Aspergillus cibarius sp. nov. isolated from meju, a brick of dried fermented soybeans in Korea, is described. The species was also found from black bean, bread and salami in the Netherlands. It is characterized by abundant yellow to reddish brown ascomata and small lenticular ascospores (4.5–5.5 μm) with a wide furrow, low equatorial crests and tuberculate or reticulate convex surface. The species was resolved as phylogenetically distinct from the other reported Aspergillus species with an Eurotium teleomorph based on multilocus sequence typing using partial fragments of the β-tubulin, calmodulin, ITS and RNA polymerase II genes

Regulation of pentose catabolic pathway genes of Aspergillus niger

The aim of this study was to obtain a better understanding of the pentose catabolism in Aspergillus niger and the regulatory systems that affect it. To this end, we have cloned and characterised the genes encoding A. niger L-arabitol dehydrogenase (ladA) and xylitol dehydrogenase (xdhA), and compared the regulation of these genes to other genes of the pentose catabolic pathway. This demonstrated that activation of the pathway depends on two transcriptional regulators, the xylanolytic activator (XlnR) and an unidentified L-arabinose specific regulator (AraR). These two regulators affect those genes of the pentose catabolic pathway that are related to catabolic conversion of their corresponding inducers (D-xylose and L-arabinose, respectively)

Comparative genomics reveals high biological diversity and specific adaptations in the industrially and medically important fungal genus Aspergillus

Background: The fungal genus Aspergillus is of critical importance to humankind. Species include those with industrial applications, important pathogens of humans, animals and crops, a source of potent carcinogenic contaminants of food, and an important genetic model. The genome sequences of eight aspergilli have already been explored to investigate aspects of fungal biology, raising questions about evolution and specialization within this genus. Results: We have generated genome sequences for ten novel, highly diverse Aspergillus species and compared these in detail to sister and more distant genera. Comparative studies of key aspects of fungal biology, including primary and secondary metabolism, stress response, biomass degradation, and signal transduction, revealed both conservation and diversity among the species. Observed genomic differences were validated with experimental studies. This revealed several highlights, such as the potential for sex in asexual species, organic acid production genes being a key feature of black aspergilli, alternative approaches for degrading plant biomass, and indications for the genetic basis of stress response. A genome-wide phylogenetic analysis demonstrated in detail the relationship of the newly genome sequenced species with other aspergilli. Conclusions: Many aspects of biological differences between fungal species cannot be explained by current knowledge obtained from genome sequences. The comparative genomics and experimental study, presented here, allows for the first time a genus-wide view of the biological diversity of the aspergilli and in many, but not all, cases linked genome differences to phenotype. Insights gained could be exploited for biotechnological and medical applications of fungi. © 2017 The Author(s)