Overexpression of the gene encoding alternative oxidase for enhanced glucose consumption in oxalic acid producing Aspergillus niger expressing oxaloacetate hydrolase gene

Generation of citric acid-hyperproducers independent of methanol effect by high-level expression of cexA encoding citrate exporter in Aspergillus tubingensis

Methanol reportedly stimulates citric acid (CA) production by Aspergillus niger and A. tubingensis; however, the underlying mechanisms remain unclear. Here, we elucidated the molecular functions of the citrate exporter gene cexA in relation to CA production by A. tubingensis WU-2223L. Methanol addition to the medium containing glucose as a carbon source markedly increased CA production by strain WU-2223L by 3.38-fold, resulting in a maximum yield of 65.5 g/L, with enhanced cexA expression. Conversely, the cexA-complementing strain with the constitutive expression promoter Ptef1 (strain LhC-1) produced 68.3 or 66.7 g/L of CA when cultivated without or with methanol, respectively. Additionally, strain LhC-2 harboring two copies of the cexA expression cassette produced 80.7 g/L of CA without methanol addition. Overall, we showed that cexA is a target gene for methanol in CA hyperproduction by A. tubingensis WU-2223L. Based on these findings, methanol-independent CA-hyperproducing strains, LhC-1 and LhC-2, were successfully generated.

A comprehensive review of recent advances in the applications and biosynthesis of oxalic acid from bio-derived substrates

Organic acids are important compounds with numerous applications in different industries. This work presents a comprehensive review of the biological synthesis of oxalic acid, an important organic acid with many industrial applications. Due to its important applications in pharmaceuticals, textiles, metal recovery, and chemical and metallurgical industries, the global demand for oxalic acid has increased. As a result, there is an increasing need to develop more environmentally friendly and economically attractive alternatives to chemical synthesis methods, which has led to an increased focus on microbial fermentation processes. This review discusses the specific strategies for microbial production of oxalic acid, focusing on the benefits of using bio-derived substrates to improve the economics of the process and promote a circular economy in comparison with chemical synthesis. This review provides a comprehensive analysis of the various fermentation methods, fermenting microorganisms, and the biochemistry of oxalic acid production. It also highlights key sustainability challenges and considerations related to oxalic acid biosynthesis, providing important direction for further research. By providing and critically analyzing the most recent information in the literature, this review serves as a comprehensive resource for understanding the biosynthesis of oxalic acid, addressing critical research gaps, and future advances in the field.

Study on the mechanism of sodium ion inhibiting citric acid fermentation in Aspergillus niger

Excessive sodium significantly inhibits citric acid fermentation by Aspergillus niger during the recycling of citric acid wastewater. This study aimed to elucidate the inhibition mechanism at the interface of physiology and transcriptomics. The results showed that excessive sodium caused a 22.3 % increase in oxalic acid secretion and a 147.6 % increase in H+-ATPase activity at the 4 h fermentation compared to the control. Meanwhile, a 13.1 % reduction in energy charge level and a 15.2 % decline in NADH content were found, which implied the effects on carbon metabolism and redox balance. In addition, transcriptomic analysis revealed that excessive sodium altered the gene expression profiles related to ATPase, hydrolase, and oxidoreductase, as well as pathways like glyoxylate metabolism, and transmembrane transport. These findings gained insights into the metabolic regulation of A. niger response to environmental stress and provided theoretical guidance for the construction of sodium-tolerant A. niger for industrial application.

Mutations in the Second Alternative Oxidase Gene: A New Approach to Group Aspergillus niger Strains

Alternative oxidase is a terminal oxidase in the branched mitochondrial electron transport chain of most fungi including Aspergillus niger (subgenus Circumdati, section Nigri). A second, paralogous aox gene (aoxB) is extant in some A. niger isolates but also present in two divergent species of the subgenus Nidulantes-A. calidoustus and A. implicatus-as well as in Penicillium swiecickii. Black aspergilli are cosmopolitan opportunistic fungi that can cause diverse mycoses and acute aspergillosis in immunocompromised individuals. Amongst the approximately 75 genome-sequenced A. niger strains, aoxB features considerable sequence variation. Five mutations were identified that rationally affect transcription or function or terminally modify the gene product. One mutant allele that occurs in CBS 513.88 and A. niger neotype strain CBS 554.65 involves a chromosomal deletion that removes exon 1 and intron 1 from aoxB. Another aoxB allele results from retrotransposon integration. Three other alleles result from point mutations: a missense mutation of the start codon, a frameshift, and a nonsense mutation. A. niger strain ATCC 1015 has a full-length aoxB gene. The A. niger sensu stricto complex can thus be subdivided into six taxa according to extant aoxB allele, which may facilitate rapid and accurate identification of individual species.

Oxalic acid: recent developments for cost-effective microbial production

Organic acids are the important compounds that have found numerous applications in various industries. Oxalic acid is one of the important organic acids with different industrial applications. Different microbes have been reported as important sources of various organic acids. Majority of studies have been carried on fungal sources for oxalic acid production. Aspergillus sp. has been found efficient oxalic acid producer. Microbial productions of metabolites including organic acids are considered cost effective and eco-friendly approach over chemical synthesis. Fermentative production of microbial oxalic acid seems to be a good alternative as compared to chemical methods. Microbial production of oxalic acid still requires the extensive and elaborated research for its commercial production from efficient microbes using cost effective substrates. The present text summarizes the production of oxalic acid, its applications and recent developments in the direction of fermentative production of microbial oxalic acid.

Screening and Functional Verification of Selectable Marker Genes for Cordyceps militaris

The selectable marker genes are necessary resistance genes for gene knockout, gene complementation, and gene overexpression in filamentous fungi. Moreover, the more sensitive the filamentous fungi are to antibiotics, the more helpful it is to screen the target transformants. In order to obtain the antibiotic (or herbicide) which can effectively inhibit the growth of Cordyceps militaris and verify the function of the corresponding resistance gene in C. militaris, the sensitivity of C. militaris to hygromycin and glufosinate ammonium was compared to determine the resistance gene that was more suitable for the screening of C. militaris transformants. The binary vector of the selectable marker gene was constructed by combining the double-joint PCR (DJ-PCR) method and the homologous recombination method, and the function of the selectable marker gene in C. militaris was verified by the Agrobacterium tumefaciens-mediated transformation method. The results showed that C. militaris was more sensitive to glufosinate ammonium than hygromycin. The growth of C. militaris could be completely inhibited by 250 μg/mL glufosinate ammonium. The expression cassette of the glufosinate ammonium resistance gene (bar gene) was successfully constructed by DJ-PCR. The binary vector pCAMBIA0390-Bar was successfully constructed by homologous recombination. The bar gene of the vector pCAMBIA0390-Bar was successfully integrated into the C. militaris genome and could be highly expressed in the transformants of C. militaris. This study will promote the identification of C. militaris gene function and reveal the biosynthetic pathways of bioactive components in C. militaris.

Aspergillus Section Fumigati Pneumonia and Oxalate Nephrosis in a Foal

Equine pulmonary aspergillosis is a rare deep mycosis often due to the hematogenous spread of hyphae after gastrointestinal tract disease. We describe herein the main clinic-pathological findings observed in a foal, which spontaneously died after showing diarrhea and respiratory distress. Necropsy and histopathological investigations allowed to diagnose pulmonary aspergillosis, which likely developed after necrotic typhlitis-colitis. Biomolecular studies identified Aspergillus section Fumigati strain as the causative agent. Notably, severe oxalate nephrosis was concurrently observed. Occasionally, oxalate nephropathy can be a sequela of pulmonary aspergillosis in humans. The present case report suggests that the renal precipitation of oxalates can occur also in horses affected by pulmonary aspergillosis and could likely contribute to the fatal outcome of the disease.

Developing Aspergillus niger as a cell factory for food enzyme production

Aspergillus niger has become one of the most important hosts for food enzyme production due to its unique food safety characteristics and excellent protein secretion systems. A series of food enzymes such as glucoamylase have been commercially produced by A. niger strains, making this species a suitable platform for the engineered of strains with improved enzyme production. However, difficulties in genetic manipulations and shortage of expression strategies limit the progress in this regard. Moreover, several mycotoxins have recently been detected in some A. niger strains, which raises the necessity for a regulatory approval process for food enzyme production. With robust strains, processing engineering strategies are also needed for producing the enzymes on a large scale, which is also challenging for A. niger, since its culture is aerobic, and non-Newtonian fluid properties are developed during submerged culture, making mixing and aeration very energy-intensive. In this article, the progress and challenges of developing A. niger for the production of food enzymes are reviewed, including its genetic manipulations, strategies for more efficient production of food enzymes, and elimination of mycotoxins for product safety.