Fumarate production with Rhizopus oryzae: utilising the Crabtree effect to minimise ethanol by-product formation

Identification of primary metabolites in fungal species of Trichophyton mentagrophyte and Trichophyton rubrum by NMR spectroscopy

BACKGROUND

Superficial mycoses are fungal infections limited to the outermost layers of the skin and its appendages. The chief causative agents of these mycoses are dermatophytes and yeasts. The diagnosis of dermatophytosis can be made by direct mycological examination with potassium hydroxide (10%-30%) of biological material obtained from patients with suspected mycosis, providing results more rapid than fungal cultures, which may take days or weeks. This information, together with clinical history and laboratory diagnosis, ensures that the appropriate treatment is initiated promptly. However, false negative results are obtained in 5%-15%, by conventional methods of diagnosis of dermatophytosis.

OBJECTIVES

To study the metabolic profiles of the commonly occurring dermatophytes by NMR spectroscopy.

PATIENTS/MATERIALS

We have used 1D and 2D Nuclear Magnetic Resonance (NMR) experiments along with Human Metabolome Database (HMDB) and Chenomx database search for identification of primary metabolites in the methanol extract of two fungal species: Trichophyton mentagrophyte (T. mentagrophyte) and Trichophyton rubrum (T. rubrum). Both standard strains and representative number of clinical isolates of these two species were investigated. Further, metabolic profiles obtained were analysed using multivariate analysis.

RESULTS

We have identified 23 metabolites in the T. mentagrophyte and another 23 metabolites in T. rubrum. Many important metabolites like trehalose, proline, mannitol, acetate, GABA and several other amino acids were detected, which provide the necessary components for fungal growth and metabolism. Altered metabolites were defined between Trichophyton mentagrophyte and T. rubrum strains.

CONCLUSION

We have detected many metabolites in the two fungal species T. mentagrophyte and T. rubrum by using NMR spectroscopy. NMR spectroscopy provides a holistic snapshot of the metabolome of an organism. Key metabolic differences were identified between the two fungal strains. We need to perform more studies on metabolite profiling of the samples from these species for their rapid diagnosis and prompt treatment.

Selective pertraction of dicarboxylic acids from simulated Rhizopus oryzae fermentation broths

Fumaric, malic and succinic acids have been selectively separated by facilitated pertraction with Amberlite LA-2, using n-heptane as liquid membrane. The feed phase consisted on viscous aqueous solution with similar mixture of carboxylic acids and viscosity as those of Rhizopus oryzae fermentation broth. Due to the differences between the acidities and molecule size of these acids, it is possible to selectively recover fumaric acid from the initial solution. The pH-gradient between the feed and stripping phases, as well as carrier concentration in the liquid membrane represent the main process parameters influencing the pertraction selectivity. Among them, Amberlite LA-2 concentration exhibits the most important control on the selectivity factor S, the maximum value of S being reached for carrier concentration of 30 g/l. The increase of feed phase viscosity amplified the magnitude of these influences on pertraction selectivity, due to the hindrance of acids diffusion towards the region where their reaction with Amberlite LA-2 occurs, effect more important for malic acid. Therefore, by modifying the viscosity from 1 to 24 cP, the maximum value of selectivity factor was increased from 12 to 18.8.

Fungal–Lactobacteria Consortia and Enzymatic Catalysis for Polylactic Acid Production

Polylactic acid (PLA) is the main biobased plastic manufactured on an industrial scale. This polymer is synthetized by chemical methods, and there is a strong demand for the implementation of clean technologies. This work focuses on the microbial fermentation of agro-industrial waste rich in starch for the production of lactic acid (LA) in a consolidated bioprocess, followed by the enzymatic synthesis of PLA. Lactic acid bacteria (LAB) and the fungus Rhizopus oryzae were evaluated as natural LA producers in pure cultures or in fungal–lactobacteria co-cultures formed by an LAB and a fungus selected for its metabolic capacity to degrade starch and to form consortia with LAB. Microbial interaction was analyzed by scanning electron microscopy and biofilm production was quantified. The results show that the fungus Talaromyces amestolkiae and Lactiplantibacillus plantarum M9MG6-B2 establish a cooperative relationship to exploit the sugars from polysaccharides provided as carbon sources. Addition of the quorum sensing molecule dodecanol induced LA metabolism of the consortium and resulted in improved cooperation, producing 99% of the maximum theoretical yield of LA production from glucose and 65% from starch. Finally, l-PLA oligomers (up to 19-LA units) and polymers (greater than 5 kDa) were synthetized by LA polycondensation and enzymatic ring-opening polymerization catalyzed by the non-commercial lipase OPEr, naturally produced by the fungus Ophiostoma piceae.

Fumaric Acid Production by R. arrhizus NRRL 1526 Using Apple Pomace Enzymatic Hydrolysates: Kinetic Modelling

Fumaric acid is one of the most promising biorefinery platform chemicals, fruit residues being a very suitable raw material for its production in second generation biorefineries. In particular, apple pomace is a plentiful residue from the apple juice industry, with apple being the second largest fruit crop in the world, with a production that increased from 46 to 86 Mtons in the 1994–2021 period. With a global apple juice production of more than 4.5 Mtons, a similar amount of apple pomace is produced yearly. In this work, apple pomace hydrolysate has been obtained by enzymatic hydrolysis and further characterized for its content in sugars, phenolics and nitrogen using different analytic methods, based on HPLC and colorimetric techniques. Previous to the use of this hydrolysate (APH), we studied if the addition of fructose to the usual glucose-rich broth could lead to high fumaric acid yields, titers and productivities. Afterwards, APH fermentation was performed and improved using different nitrogen initial amounts, obtaining production yields (0.32 gFumaric acid/gconsumed sugar) similar to those obtained with synthetic media (0.38 gFumaric acid/gconsumed sugar). Kinetic modelling was employed to evaluate, explain, and understand the experimental values and trends of relevant components in the fermentation broth as functions of the bioprocess time, proposing a suitable reaction scheme and a non-structured, non-segregated kinetic model based on it.

Rhizopus oryzae for Fumaric Acid Production: Optimising the Use of a Synthetic Lignocellulosic Hydrolysate

The hydrolysis of lignocellulosic biomass opens an array of bioconversion possibilities for producing fuels and chemicals. Microbial fermentation is particularly suited to the conversion of sugar-rich hydrolysates into biochemicals. Rhizopus oryzae ATCC 20344 was employed to produce fumaric acid from glucose, xylose, and a synthetic lignocellulosic hydrolysate (glucose–xylose mixture) in batch and continuous fermentations. A novel immobilised biomass reactor was used to investigate the co-fermentation of xylose and glucose. Ideal medium conditions and a substrate feed strategy were then employed to optimise the production of fumaric acid. The batch fermentation of the synthetic hydrolysate at optimal conditions (urea feed rate 0.625mgL−1h−1 and pH 4) produced a fumaric acid yield of 0.439gg−1. A specific substrate feed rate (0.164gL−1h−1) that negated ethanol production and selected for fumaric acid was determined. Using this feed rate in a continuous fermentation, a fumaric acid yield of 0.735gg−1 was achieved; this was a 67.4% improvement. A metabolic analysis helped to determine a continuous synthetic lignocellulosic hydrolysate feed rate that selected for fumaric acid production while achieving the co-fermentation of glucose and xylose, thus avoiding the undesirable carbon catabolite repression. This work demonstrates the viability of fumaric acid production from lignocellulosic hydrolysate; the process developments discovered will pave the way for an industrially viable process.

The Effect of pH, Metal Ions, and Insoluble Solids on the Production of Fumarate and Malate by Rhizopus delemar in the Presence of CaCO3

Calcium carbonate has been extensively used as a neutralising agent in acid-forming microbial processes. The effect of increasing calcium carbonate concentrations on Rhizopus delemar has not been previously investigated. In this study, an evaluation of fumaric acid (FA) and malic acid (MA) production was conducted at three CaCO3 concentrations in shake flask cultivations. Increased CaCO3 concentrations resulted in the co-production of FA and MA in the first 55 h of the fermentation (regime 1), and the subsequent depletion of FA thereafter (regime 2). Three factors were highlighted as likely causes of this response: insoluble solids, metal ion concentrations, and pH. Further shake flask cultivations as well as a continuous fermentation with immobilised R. delemar were used to explore the effect of the three factors on regime 1 and 2. Insoluble solids were found to have no effect on the response in either regime 1 or 2. Increasing the aqueous calcium ion concentrations to 10g/L resulted in a three-fold increase in MA titres (regime 1). Moreover, an increase in pH above 7 was associated with a drop in FA concentrations in regime 2. Further tests established that this was due to the hydration of FA to MA, influenced by high pH conditions ( 7 or higher), nitrogen starvation, and glucose depletion. Anaerobic conditions were also found to significantly improve the hydration process. This study presents the first investigation in which the production of FA followed by in situ hydration of FA to MA with R. delemar has been achieved.

Fractionation of dicarboxylic acids produced by Rhizopus oryzae using reactive extraction

Fumaric, malic, and succinic acids have been selectively separated from their mixture obtained by Rhizopus oryzae fermentation using reactive extraction with Amberlite LA-2 dissolved in three solvents with different dielectric constants (n-heptane, n-butyl acetate, and dichloromethane). This technique allows recovering preferentially fumaric acid from the mixture, the raffinate containing only malic and succinic acids. The extractant concentration and organic phase polarity control the efficiency and selectivity of acids extraction. The increase of aqueous phase viscosity reduces the extraction yield for all studied acids, but exhibits a positively effect on separation selectivity. By using Amberlite LA-2 concentration equal to that stoichiometrically required for interfacial reaction with fumaric acid and mixing intensity which does not allow higher diffusion rates for larger molecules (malic and succinic acids), the maximum value of fumaric acid extraction rate exceeds 90%, while the selectivity factor value becomes 20. Regardless of the extraction system, the complete separation of fumaric acid from their mixture is possible by multi-stage extraction process, adjusting the extractant concentration in each stage. At higher values of aqueous phase viscosity, more extraction stages are required, while the increase of solvent polarity reduce the required number of stages for total recovery of fumaric acid.

Continuous Production of Fumaric Acid with Immobilised Rhizopus oryzae: The Role of pH and Urea Addition

Fumaric acid is widely used in the food and beverage, pharmaceutical and polyester resin industries. Rhizopus oryzae is the most successful microorganism at excreting fumaric acid compared to all known natural and genetically modified organisms. It has previously been discovered that careful control of the glucose feed rate can eliminate the by-product formation of ethanol. Two key parameters affecting fumaric acid excretion were identified, namely the medium pH and the urea feed rate. A continuous fermentation with immobilised R. oryzae was utilised to determine the effect of these parameters. It was found that the selectivity for fumaric acid production increased at high glucose consumption rates for a pH of 4, different from the trend for pH 5 and 6, achieving a yield of 0.93 gg−1. This yield is higher than previously reported in the literature. Varying the urea feed rate to 0.255 mgL−1h−1 improved the yield of fumaric acid but experienced a lower glucose uptake rate compared to higher urea feed rates. An optimum region has been found for fumaric acid production at pH 4, a urea feed rate of 0.625 mgL−1h−1 and a glucose feed rate of 0.329 gL−1h−1.

Direct Extraction of Fumaric Acid from Rhizopus oryzae Suspensions-Interfacial Mass Transfer

Experimental studies on the reactive extraction of fumaric acid with Amberlite LA-2 from Rhizopus oryzae suspensions using three solvents with different dielectric constants varying from 9.08 to 1.90 (dichloromethane, n-butyl acetate, and n-heptane, respectively) underlined the particular behavior of the extraction system in the presence of fungal biomass. The interfacial mass flow of the reaction product was found to be significantly affected by the biomass, due mainly to its adsorption onto the phase separation interface, this leading to the appearance of a physical barrier against the solute's transfer. However, the magnitude of the adsorption phenomenon was found to depend on Rhizopus oryzae's affinity for the solvent phase, which increased significantly from dichloromethane to n-heptane. The negative influence of the biomass on the interfacial mass transfer can be partially counteracted by adding 1-octanol into the organic phase, improving the solvent's ability to solve the fumaric acid-Amberlite LA-2 complex and simplifying the reactive extraction mechanism, effects that were found to be more important for low-polar solvents. Consequently, for the same mixing intensity, the maximum amplification factor was reached for n-heptane, its value being almost 5-6 times higher than that obtained for dichloromethane and over 2 times higher than that obtained with n-butyl acetate.

Fumaric acid production using alternate fermentation mode by immobilized Rhizopus oryzae-a greener production strategy

The current work investigates the impact of using immobilized Rhizopus oryzae NRRL 1526 for bioproduction of fumaric acid using agro-industrial residues as feedstock. This use of agro-industrial residues, a renewable feedstock, for the production of bio-based platform chemical makes the process cost-competitive as well as greener by preventing the release of assimilable organic carbon to the environment, thereby reducing the generation of greenhouse gases. Immobilization of R. oryzae has been proposed previously to alleviate operational difficulties confronted during free mycelial fungal fermentation. To this effect, three synthetic refuse materials namely polystyrene foam, polyester sponge and polyurethane foam were investigated for their suitability towards fumaric acid bioproduction. Polystyrene foam was identified as the most suitable support material for immobilization as well as fumaric acid production. In addition to the considerable reduction in the lag-phase (from 48 to 24 h) the reduction in the size of the support material from cubes of 1 cm to beads of 0.1-0.3 cm led to a 42% improvement in fumaric acid production (27 g/L against 19 g/L). Growing the polystyrene foam bead immobilized R. oryzae on apple pomace ultrafiltration sludge as sole feedstock yielded a final fumaric acid titer of 7.9 g/L whereas free mycelial fermentation yielded 6.3 g/L. Moreover, upon operating the fermentation with intermittent feeding, a three-fold increase (1.7 g/L to 5.1 g/L) in fumaric acid production was obtained upon supplementation of the apple pomace sludge media with molasses, an agro-industrial residue, as feed.

Potential Valorization of Organic Waste Streams to Valuable Organic Acids through Microbial Conversion: A South African Case Study

The notion of a “biobased economy” in the context of a developing country such as South Africa (SA) necessitates the development of technologies that utilize sustainable feedstocks, have simple and robust operations, are feasible at small scale and produce a variety of valuable bioproducts, thus fitting the biorefinery concept. This case study focuses on the microbial production of higher-value products from selected organic waste streams abundant in the South African agricultural sector using microbes adapted to utilize different parts of biomass waste streams. A ruminant-based carboxylate platform based on mixed or undefined anaerobic co-cultures of rumen microorganisms can convert the carbohydrate polymers in the lignocellulosic part of organic waste streams to carboxylic acids that can be upgraded to biofuels or green chemicals. Furthermore, yeast and fungi can convert the simpler carbohydrates (such as the sugars and malic acid in grape and apple pomace) to ethanol and high-value carboxylic acids, such as lactic, fumaric, succinic and citric acid. This review will discuss the combinational use of the ruminal carboxylate platform and native or recombinant yeasts to valorize biomass waste streams through the production of higher-value organic acids with various applications.

Engineering microorganisms for the biosynthesis of dicarboxylic acids

Dicarboxylic acids (DCAs) are important commodity chemicals which have been widely applied in polymer, food and pharmaceutical industries. Biosynthesis of DCAs from renewable carbon sources represents a promising alternative to chemical synthesis. Over the years, the recombinant strains have been constructed to produce an increasing number of DCAs. In this review, recent advances on the microbial synthesis of various DCAs have been summarized and categorized into three groups: the tricarboxylic acid cycle-derived, lysine metabolism-related, and aromatic compounds degradation-derived DCAs. We focused mainly on the metabolic engineering and synthetic biology strategies for improving the production efficiency, including metabolic flux analysis, fine-tuning of gene expression, cofactor balancing, metabolic compartmentalization, dynamic regulation and co-culture to regulate the production at multiple levels. The current challenges and perspectives have also been discussed.

Enhancement of Monascus yellow pigments production by activating the cAMP signalling pathway in Monascus purpureus HJ11

BACKGROUND

Monascus azaphilone pigments (MonAzPs), which were produced by Monascus species, have been used as important food colorant and food supplements for more than one billion people during their daily life. Moreover, MonAzPs recently have received more attention because of their diverse physiological activities. However, the high microbial production of MonAzPs is still not always guaranteed. Herein, the aim of this study was to develop an efficient biotechnological process for MonAzPs production.

RESULTS

In this study, exogenous cyclic adenosine monophosphate (cAMP) treatment not only induced MonAzPs production, but also stimulated the expression of a cAMP phosphodiesterase gene, named as mrPDE, in M. purpureus HJ11. Subsequently, MrPDE was identified as a cAMP phosphodiesterase by in vitro enzymatic reaction with purified enzyme. Further, a gene knockout mutant of mrPDE was constructed to verify the activation of cAMP signalling pathway. Deletion of mrPDE in M. purpureus HJ11 improved cAMP concentration by 378% and enhanced PKA kinase activity 1.5-fold, indicating that activation of cAMP signalling pathway was achieved. The ΔmrPDE strain produced MonAzPs at 8563 U/g, with a 2.3-fold increase compared with the WT strain. Moreover, the NAPDH/NADP⁺ ratio of the ΔmrPDE strain was obviously higher than that of the wild type strain, which led to a higher proportion of yellow MonAzPs. With fed-batch fermentation of the ΔmrPDE strain, the production and yield of MonAzPs achieved 332.1 U/mL and 8739 U/g.

CONCLUSIONS

A engineered M. purpureus strain for high MonAzPs production was successfully developed by activating the cAMP signalling pathway. This study not only describes a novel strategy for development of MonAzPs-producing strain, but also provides a roadmap for engineering efforts towards the production of secondary metabolism in other filamentous fungi.