Biotechnological production of gluconic acid: future implications

Waste biorefineries using filamentous ascomycetes fungi: Present status and future prospects

Filamentous ascomycetes fungi have had important roles in natural cycles, and are already used industrially for e.g. supplying of citric, gluconic and itaconic acids as well as many enzymes. Faster human activities result in higher consumption of our resources and producing more wastes. Therefore, these fungi can be explored to use their capabilities to convert back wastes to resources. The present paper reviews the capabilities of these fungi in growing on various residuals, producing lignocellulose-degrading enzymes and production of organic acids, ethanol, pigments, etc. Particular attention has been on Aspergillus, Fusarium, Neurospora and Monascus genera. Since various species are used for production of human food, their biomass can be considered for feed applications and so biomass compositional characteristics as well as aspects related to culture in bioreactor are also provided. The review has been further complemented with future research avenues.

A simple novel approach for real-time monitoring of sodium gluconate production by on-line physiological parameters in batch fermentation by Aspergillus niger

In this paper, approach for real-time monitoring of sodium gluconate (SG) fermentation was established for the first time by the equations which can calculate real-time key-parameters by on-line physiological data. Based on this approach, limiting factors were found out in initial fermentation F1 and then step-wise agitation increase and improved medium recipe were proposed in fermentation F2 and F3, respectively. The highest average SG production rate (16.58±0.91 g L(-1) h(-1)) was achieved in fermentation F3, which was 104.2% and 48.0% higher than those in fermentation F1 and F2, respectively. Meanwhile, due to shorter fermentation period (decreased from 34 h to 18.7 h), lower biomass (about 1.5 g L(-1)) and less by-product accumulation, the overall yield of 0.943±0.012 (mol mol(-1)) in fermentation F3 increased more than 16.0% compared to fermentation F1. This approach had been successfully applied to industrial fermentation and greatly improved SG production.

V and Ni recovery from a vanadium-rich power plant residual ash using acid producing fungi: Aspergillus niger and Penicillium simplicissimum

Bioleaching of V and Ni from a vanadium-rich power plant residual (PPR) ash using Aspergillus niger and Penicillium simplicissimum was investigated.

Plasmalyte: No Longer a Culprit in Causing False-Positive Galactomannan Test Results

False-positive galactomannan (GM) results have been reported in patients treated with gluconate-containing solutions, such as Plasmalyte. The GM optical density index was tested on 33 distinct batches of Plasmalyte and was found to be negative in all of the batches, confirming that Plasmalyte is no longer a cause of false-positive GM results.

Kinetic analysis of gluconate phosphorylation by human gluconokinase using isothermal titration calorimetry

Gluconate is a commonly encountered nutrient, which is degraded by the enzyme gluconokinase to generate 6-phosphogluconate. Here we used isothermal titration calorimetry to study the properties of this reaction. ΔH, KM and kcat are reported along with substrate binding data. We propose that the reaction follows a ternary complex mechanism, with ATP binding first. The reaction is inhibited by gluconate, as it binds to an Enzyme-ADP complex forming a dead-end complex. The study exemplifies that ITC can be used to determine mechanisms of enzyme catalyzed reactions, for which it is currently not commonly applied.

Impact of gluconic fermentation of strawberry using acetic acid bacteria on amino acids and biogenic amines profile

This paper studies the amino acid profile of beverages obtained through the fermentation of strawberry purée by a surface culture using three strains belonging to different acetic acid bacteria species (one of Gluconobacter japonicus, one of Gluconobacter oxydans and one of Acetobacter malorum). An HPLC-UV method involving diethyl ethoxymethylenemalonate (DEEMM) was adapted and validated. From the entire set of 21 amino acids, multiple linear regressions showed that glutamine, alanine, arginine, tryptophan, GABA and proline were significantly related to the fermentation process. Furthermore, linear discriminant analysis classified 100% of the samples correctly in accordance with the microorganism involved. G. japonicus consumed glucose most quickly and achieved the greatest decrease in amino acid concentration. None of the 8 biogenic amines were detected in the final products, which could serve as a safety guarantee for these strawberry gluconic fermentation beverages, in this regard.

Manipulation of fungal development as source of novel secondary metabolites for biotechnology

Fungal genomics revealed a large potential of yet-unexplored secondary metabolites, which are not produced during vegetative growth. The discovery of novel bioactive compounds is increasingly gaining importance. The high number of resistances against established antibiotics requires novel drugs to counteract increasing human and animal mortality rates. In addition, growth of plant pathogens has to be controlled to minimize harvest losses. An additional critical issue is the post-harvest production of deleterious mycotoxins. Fungal development and secondary metabolite production are linked processes. Therefore, molecular regulators of development might be suitable to discover new bioactive fungal molecules or to serve as targets to control fungal growth, development, or secondary metabolite production. The fungal impact is relevant as well for our healthcare systems as for agriculture. We propose here to use the knowledge about mutant strains discovered in fungal model systems for a broader application to detect and explore new fungal drugs or toxins. As examples, mutant strains impaired in two conserved eukaryotic regulatory complexes are discussed. The COP9 signalosome (CSN) and the velvet complex act at the interface between development and secondary metabolism. The CSN is a multi-protein complex of up to eight subunits and controls the activation of CULLIN-RING E3 ubiquitin ligases, which mark substrates with ubiquitin chains for protein degradation by the proteasome. The nuclear velvet complex consists of the velvet-domain proteins VeA and VelB and the putative methyltransferase LaeA acting as a global regulator for secondary metabolism. Defects in both complexes disturb fungal development, light perception, and the control of secondary metabolism. The potential biotechnological relevance of these developmental fungal mutant strains for drug discovery, agriculture, food safety, and human healthcare is discussed.

Acetic Acid bacteria: physiology and carbon sources oxidation

Acetic acid bacteria (AAB) are obligately aerobic bacteria within the family Acetobacteraceae, widespread in sugary, acidic and alcoholic niches. They are known for their ability to partially oxidise a variety of carbohydrates and to release the corresponding metabolites (aldehydes, ketones and organic acids) into the media. Since a long time they are used to perform specific oxidation reactions through processes called "oxidative fermentations", especially in vinegar production. In the last decades physiology of AAB have been widely studied because of their role in food production, where they act as beneficial or spoiling organisms, and in biotechnological industry, where their oxidation machinery is exploited to produce a number of compounds such as l-ascorbic acid, dihydroxyacetone, gluconic acid and cellulose. The present review aims to provide an overview of AAB physiology focusing carbon sources oxidation and main products of their metabolism.

Inferring the metabolism of human orphan metabolites from their metabolic network context affirms human gluconokinase activity

Metabolic network reconstructions define metabolic information within a target organism and can therefore be used to address incomplete metabolic information. In the present study we used a computational approach to identify human metabolites whose metabolism is incomplete on the basis of their detection in humans but exclusion from the human metabolic network reconstruction RECON 1. Candidate solutions, composed of metabolic reactions capable of explaining the metabolism of these compounds, were then identified computationally from a global biochemical reaction database. Solutions were characterized with respect to how metabolites were incorporated into RECON 1 and their biological relevance. Through detailed case studies we show that biologically plausible non-intuitive hypotheses regarding the metabolism of these compounds can be proposed in a semi-automated manner, in an approach that is similar to de novo network reconstruction. We subsequently experimentally validated one of the proposed hypotheses and report that C9orf103, previously identified as a candidate tumour suppressor gene, encodes a functional human gluconokinase. The results of the present study demonstrate how semi-automatic gap filling can be used to refine and extend metabolic reconstructions, thereby increasing their biological scope. Furthermore, we illustrate how incomplete human metabolic knowledge can be coupled with gene annotation in order to prioritize and confirm gene functions.

Acidic organic compounds in beverage, food, and feed production

Organic acids and their derivatives are frequently used in beverage, food, and feed production. Acidic additives may act as buffers to regulate acidity, antioxidants, preservatives, flavor enhancers, and sequestrants. Beneficial effects on animal health and growth performance have been observed when using acidic substances as feed additives. Organic acids could be classified in groups according to their chemical structure. Each group of organic acids has its own specific properties and is used for different applications. Organic acids with low molecular weight (e.g. acetic acid, lactic acid, and citric acid), which are part of the primary metabolism, are often produced by fermentation. Others are produced more economically by chemical synthesis based on petrochemical raw materials on an industrial scale (e.g. formic acid, propionic and benzoic acid). Biotechnology-based production is of interest due to legislation, consumer demand for natural ingredients, and increasing environmental awareness. In the United States, for example, biocatalytically produced esters for food applications can be labeled as "natural," whereas identical conventional acid catalyst-based molecules cannot. Natural esters command a price several times that of non-natural esters. Biotechnological routes need to be optimized regarding raw materials and yield, microorganisms, and recovery methods. New bioprocesses are being developed for organic acids, which are at this time commercially produced by chemical synthesis. Moreover, new organic acids that could be produced with biotechnological methods are under investigation for food applications.

False-positive Aspergillus antigenemia due to blood product conditioning fluids

The presence of Aspergillus antigens in blood transfusion components from different manufacturers was analyzed. Galacomannans were found in transfused patients, pooled platelet concentrates, fresh frozen plasma, and packed red cells collected using Fresenius Kabi bags. Galacomannans were also found in blood collection anticoagulant and platelet additive solution from this manufacturer.

A novel biochemical route for fuels and chemicals production from cellulosic biomass

The conventional biochemical platform featuring enzymatic hydrolysis involves five key steps: pretreatment, cellulase production, enzymatic hydrolysis, fermentation, and product recovery. Sugars are produced as reactive intermediates for subsequent fermentation to fuels and chemicals. Herein, an alternative biochemical route is proposed. Pretreatment, enzymatic hydrolysis and cellulase production is consolidated into one single step, referred to as consolidated aerobic processing, and sugar aldonates are produced as the reactive intermediates for biofuels production by fermentation. In this study, we demonstrate the viability of consolidation of the enzymatic hydrolysis and cellulase production steps in the new route using Neurospora crassa as the model microorganism and the conversion of cellulose to ethanol as the model system. We intended to prove the two hypotheses: 1) cellulose can be directed to produce cellobionate by reducing β-glucosidase production and by enhancing cellobiose dehydrogenase production; and 2) both of the two hydrolysis products of cellobionate—glucose and gluconate—can be used as carbon sources for ethanol and other chemical production. Our results showed that knocking out multiple copies of β-glucosidase genes led to cellobionate production from cellulose, without jeopardizing the cellulose hydrolysis rate. Simulating cellobiose dehydrogenase over-expression by addition of exogenous cellobiose dehydrogenase led to more cellobionate production. Both of the two hydrolysis products of cellobionate: glucose and gluconate can be used by Escherichia coli KO 11 for efficient ethanol production. They were utilized simultaneously in glucose and gluconate co-fermentation. Gluconate was used even faster than glucose. The results support the viability of the two hypotheses that lay the foundation for the proposed new route.

Galactomannan antigenemia after infusion of gluconate-containing Plasma-Lyte

We demonstrated that sodium gluconate was the factor causing false-positive galactomannan (GM) antigenemia of Plasma-Lyte hydration solution. Infusion of sodium gluconate-containing solution but not gluconate-free Plasma-Lyte resulted in positive serum GM antigenemia. Serum GM concentrations also correlated with the volume and in vitro concentrations of GM within gluconate-containing solutions of infused Plasma-Lyte.

The zero-sum game of pathway optimization: emerging paradigms for tuning gene expression

With increasing price volatility and growing awareness of the lack of sustainability of traditional chemical synthesis, microbial chemical production has been tapped as a promising renewable alternative for the generation of diverse, stereospecific compounds. Nonetheless, many attempts to generate them are not yet economically viable. Due to the zero-sum nature of microbial resources, traditional strategies of pathway optimization are attaining minimal returns. This result is in part a consequence of the gross changes in host physiology resulting from such efforts and underscores the need for more precise and subtle forms of gene modulation. In this review, we describe alternative strategies and emerging paradigms to address this problem and highlight potential solutions from the emerging field of synthetic biology.

In vitro study of the antioxidative properties of the glucose derivatives against oxidation of plasma components

Oxidative stress has been implicated in the pathogenesis of variety of diseases. Since the endogenous antioxidant defense may be not adequate to counteract the enhanced generation of oxidants, a growing interest in research for exogenous nutrients has been observed. The present study was designed to assess in vitro the antioxidative properties of the glucose derivatives: calcium D-glucarate, D-gluconic acid lactone, and sodium D-gluconate (0.5-3 mM) in the protection of plasma proteins and lipids, against the damage caused by 0.1 mM peroxynitrite (ONOO⁻). Exposure of plasma to ONOO⁻ resulted in carbonyl groups increase, 3-nitrotyrosine (3-NT) formation, reduction in thiol groups, and enhanced lipid peroxidation. D-gluconic acid lactone and sodium D-gluconate effectively decreased 3-NT formation; the antinitrative action of calcium D-glucarate was less effective. In plasma samples incubated with ONOO⁻ and tested compounds, the level of carbonyl groups was decreased in comparison to plasma samples treated only with ONOO⁻. The level of protein -SH groups and glutathione was significantly higher in the presence of glucose derivatives than in plasma samples treated with ONOO⁻ only. All the tested compounds had the inhibitory effect on the peroxynitrite-induced plasma lipids peroxidation. The results obtained from our work indicate that calcium D-glucarate, D-gluconic acid lactone, and sodium D-gluconate may partly protect plasma proteins and lipids against peroxynitrite-induced damages.

Gluconic acid production by Aspergillus terreus

AIM

Aspergillus terreus produces itaconic acid at low pH but lovastatin and other secondary metabolites at higher pH in the fermentation. The utilization of glucose as a carbon substrate was investigated for secondary metabolite production by A. terreus.

METHODS AND RESULTS

With a starting pH of 6.5, glucose was rapidly metabolized to gluconic acid by the wild-type strain and by transformants harbouring Aspergillus niger genes encoding 6-phosphofructo-1-kinases with superior kinetic and regulatory properties for bioproduction of metabolites from glucose. On exhaustion of the glucose in batch fermentations, the accumulated gluconic acid was utilized as a carbon source.

CONCLUSIONS

A novel pathway of glucose catabolism was demonstrated in A. terreus, a species whose wild type is, without any strain development, capable of producing gluconic acid at high molar conversion efficiency (up to 0.7 mol mol(-1) glucose consumed).

SIGNIFICANCE AND IMPACT OF THE STUDY

Aspergillus terreus is a potential novel producer organism for gluconic acid, a compound with many uses as a bulk chemical. With a new knowledge of glucose catabolism by A. terreus, fermentation strategies for secondary metabolite production can be devised with glucose feeding using feedback regulation by pH.

Metabolic model integration of the bibliome, genome, metabolome and reactome of Aspergillus niger

The release of the genome sequences of two strains of Aspergillus niger has allowed systems-level investigations of this important microbial cell factory. To this end, tools for doing data integration of multi-ome data are necessary, and especially interesting in the context of metabolism. On the basis of an A. niger bibliome survey, we present the largest model reconstruction of a metabolic network reported for a fungal species. The reconstructed gapless metabolic network is based on the reportings of 371 articles and comprises 1190 biochemically unique reactions and 871 ORFs. Inclusion of isoenzymes increases the total number of reactions to 2240. A graphical map of the metabolic network is presented. All levels of the reconstruction process were based on manual curation. From the reconstructed metabolic network, a mathematical model was constructed and validated with data on yields, fluxes and transcription. The presented metabolic network and map are useful tools for examining systemwide data in a metabolic context. Results from the validated model show a great potential for expanding the use of A. niger as a high-yield production platform.