Simultaneous Production and Recovery of Fumaric Acid from Immobilized Rhizopus oryzae with a Rotary Biofilm Contactor and an Adsorption Column

Biofilms for Production of Chemicals and Energy

The twenty-first century will be the century of biology. This is not only because of breakthrough advances in molecular biology tools but also because we need to reinvent our economy based on the biological principles of energy efficiency and sustainability. Consequently, new tools for production routines must be developed to help produce platform chemicals and energy sources based on sustainable resources. In this context, biofilm-based processes have the potential to impact future production processes, because they can be carried out continuously and with robust stationary biocatalysts embedded in an extracellular matrix with different properties. We review productive biofilm systems used for heterotrophic and lithoautotrophic production and attempt to identify fundamental reasons why they may be particularly suitable as future production systems.

Production of Primary Metabolites by Rhizopus stolonifer, Causal Agent of Almond Hull Rot Disease

Species in the fungal genus Rhizopus are able to convert simple sugars into primary metabolites such as fumaric acid, lactic acid, citric acid, and, to a lesser extent, malic acid in the presence of specific carbon and nitrogen sources. This ability has been linked to plant pathogenicity. Rhizopus stolonifer causes hull rot disease in almonds, symptoms of which have been previously associated with the fungus's production of fumaric acid. Six isolates of R. stolonifer taken from infected almond hulls were grown in artificial media amended with one of four carbon sources (glucose, fructose, sucrose, and xylose) and two nitrogen sources (asparagine and ammonium sulphate) chosen based on almond hull composition and used in industry. Proton nuclear magnetic resonance (1H NMR)-based metabolomics identified that R. stolonifer could metabolise glucose, fructose, sucrose, and to a lesser extent xylose, and both nitrogen sources, to produce three metabolites, i.e., fumaric acid, lactic acid, and ethanol, under in vitro conditions. Sugar metabolisation and acid production were significantly influenced by sugar source and isolates, with five isolates depleting glucose most rapidly, followed by fructose, sucrose, and then xylose. The maximum amounts of metabolites were produced when glucose was the carbon source, with fumaric acid produced in higher amounts than lactic acid. Isolate 19A-0069, however, preferred sucrose as the carbon source, and Isolate 19A-0030 produced higher amounts of lactic acid than fumaric acid. This is the first report, to our knowledge, of R. stolonifer producing lactic acid in preference to fumaric acid. Additionally, R. stolonifer isolate 19-0030 was inoculated into Nonpareil almond fruit on trees grown under high- and low-nitrogen and water treatments, and hull compositions of infected and uninfected fruit were analysed using 1H NMR-based metabolomics. Glucose and asparagine content of uninfected hulls was influenced by the nitrogen and water treatments provided to the trees, being higher in the high-nitrogen and water treatments. In infected hulls, glucose and fructose were significantly reduced but not sucrose or xylose. Large amounts of both fumaric and lactic acid were produced, particularly under high-nitrogen treatments. Moreover, almond shoots placed in dilute solutions of fumaric acid or lactic acid developed leaf symptoms very similar to the 'strike' symptoms seen in hull rot disease in the field, suggesting both acids are involved in causing disease.

Fumaric acid: fermentative production, applications and future perspectives

The rising prices of petroleum-based chemicals and the growing apprehension about food safety and dairy supplements have reignited interest in fermentation process to produce fumaric acid. This article reviews the main issues associated with industrial production of fumaric acid. Different approaches such as strain modulation, morphological control, selection of substrate and fermentative separation have been addressed and discussed followed by their potential towards production of fumaric acid at industrial scale is highlighted. The employment of biodegradable wastes as substrates for the microorganisms involved in fumaric acid synthesis has opened an economic and green route for production of the later on a commercial scale. Additionally, the commercial potential and technological approaches to the augmented fumaric acid derivatives have been discussed. Conclusion of the current review reveals future possibilities for microbial fumaric acid synthesis.

Advances on Bacterial and Fungal Biofilms for the Production of Added-Value Compounds

Simple Summary

The production of bio-based materials, including organic acids, antibiotics, enzymes, ethanol, and hydrogen, is generally done by the cultivation of suspended cells rather than using immobilized cells. However, several studies suggest the application of productive biofilms as a reliable alternative for biocatalysis, with many advantages over suspended-growth systems. This review gives an overview of the breakthrough in the application of biofilm platforms for the sustainable production of valuable compounds, with particular insight into the latest advances in the production of recombinant proteins. Productive biofilms are shown to improve production rates and product yields, demonstrating great potential for industrial applications.

Abstract

In recent years, abundant research has been performed on biofilms for the production of compounds with biotechnological and industrial relevance. The use of biofilm platforms has been seen as a compelling approach to producing fine and bulk chemicals such as organic acids, alcohols, and solvents. However, the production of recombinant proteins using this system is still scarce. Biofilm reactors are known to have higher biomass density, operational stability, and potential for long-term operation than suspended cell reactors. In addition, there is an increasing demand to harness industrial and agricultural wastes and biorefinery residues to improve process sustainability and reduce production costs. The synthesis of recombinant proteins and other high-value compounds is mainly achieved using suspended cultures of bacteria, yeasts, and fungi. This review discusses the use of biofilm reactors for the production of recombinant proteins and other added-value compounds using bacteria and fungi.

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.

Enhanced l-Malic Acid Production by Aspergillus oryzae DSM 1863 Using Repeated-Batch Cultivation

l-Malic acid is a C4-dicarboxylic acid and a potential key building block for a bio-based economy. At present, malic acid is synthesized petrochemically and its major market is the food and beverages industry. In future, malic acid might also serve as a building block for biopolymers or even replace the commodity chemical maleic anhydride. For a sustainable production of l-malic acid from renewable resources, the microbial synthesis by the mold Aspergillus oryzae is one possible route. As CO₂ fixation is involved in the biosynthesis, high yields are possible, and at the same time greenhouse gases can be reduced. In order to enhance the production potential of the wild-type strain Aspergillus oryzae DSM 1863, process characteristics were studied in shake flasks, comparing batch, fed-batch, and repeated-batch cultivations. In the batch process, a prolonged cultivation time led to malic acid consumption. Keeping carbon source concentration on a high level by pulsed feeding could prolong cell viability and cultivation time, however, did not result in significant higher product levels. In contrast, continuous malic acid production could be achieved over six exchange cycles and a total fermentation time of 19 days in repeated-batch cultivations. Up to 178 g/L l-malic acid was produced. The maximum productivity (0.90 ± 0.05 g/L/h) achieved in the repeated-batch cultivation had more than doubled than that achieved in the batch process and also the average productivity (0.42 ± 0.03 g/L/h for five exchange cycles and 16 days) was increased considerably. Further repeated-batch experiments confirmed a positive effect of regular calcium carbonate additions on pH stability and malic acid synthesis. Besides calcium carbonate, nitrogen supplementation proved to be essential for the prolonged malic acid production in repeated-batch. As prolonged malic acid production was only observed in cultivations with product removal, product inhibition seems to be the major limiting factor for malic acid production by the wild-type strain. This study provides a systematic comparison of different process strategies under consideration of major influencing factors and thereby delivers important insights into natural l-malic acid production.

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.

Enhanced production of ε-poly-L-lysine by immobilized Streptomyces ahygroscopicus through repeated-batch or fed-batch fermentation with in situ product removal

ε-Poly-L-lysine (ε-PL) is a naturally-occurring L-lysine homopolymer having a broad-spectrum antimicrobial activity and used widely as a food preservative. In the present study, the combined use of immobilization and in situ product removal (ISPR) was evaluated for the production of ε-PL by Streptomyces ahygroscopicus GIM8. Results showed that ε-PL production in the flask cultures decreased from 0.84 to 0.38-0.56 g/L upon immobilization on loofah sponge with different amounts (0.5-3 g in 50 mL medium in a flask). By applying continuous ISPR to the immobilized flask cultures, ε-PL production as high as 3.51 g/L was obtained compared to 0.51 g/L of the control. A satisfactory titer of 1.84 g/L ε-PL could also be achieved with intermittent ISRP (three cycles of ISPR operation during cultivation). Further investigation showed that low levels of ε-PL retained in the broth appeared to favor its biosynthesis. In the repeated-batch fermentation in a 5 L immobilized bioreactor, with continuous ISPR, the final average ε-PL concentration and productivity were 3.35 g/L and 0.797 g/L/day, respectively, and 3.18 g/L and 0.756 g/L/day for the alternative (intermittent ISPR), in comparison to 1.16 g/L and 0.277 g/L/day with no ISPR usage. In the fed-batch fermentation with immobilized cells, the combined use of intermittent ISPR and extra nutrient feeding increased ε-PL concentration and productivity up to 24.57 g/L and 9.34 g/L/day. The fermentation processes developed could serve as an effective approach for ε-PL production and, moreover, the combination could greatly simplify downstream processing for ε-PL separation and purification.

Socio-Economic and Environmental Impacts of Biomass Valorisation: A Strategic Drive for Sustainable Bioeconomy

In the late twentieth century, the only cost-effective opportunity for waste removal cost at least several thousand dollars, but nowadays, a lot of improvement has occurred. The biomass and waste generation problems attracted concerned authorities to identify and provide environmentally friendly sustainable solutions that possess environmental and economic benefits. The present study emphasises the valorisation of biomass and waste produced by domestic and industrial sectors. Therefore, substantial research is ongoing to replace the traditional treatment methods that potentially acquire less detrimental effects. Synthetic biology can be a unique platform that invites all the relevant characters for designing and assembling an efficient program that could be useful to handle the increasing threat for human beings. In the future, these engineered methods will not only revolutionise our lives but practically lead us to get cheaper biofuels, producing bioenergy, pharmaceutics, and various biochemicals. The bioaugmentation approach concomitant with microbial fuel cells (MFC) is an example that is used to produce electricity from municipal waste, which is directly associated with the loading of waste. Beyond the traditional opportunities, herein, we have spotlighted the new advances in pertinent technology closely related to production and reduction approaches. Various integrated modern techniques and aspects related to the industrial sector are also discussed with suitable examples, including green energy and other industrially relevant products. However, many problems persist in present-day technology that requires essential efforts to handle thoroughly because significant valorisation of biomass and waste involves integrated methods for timely detection, classification, and separation. We reviewed and proposed the anticipated dispensation methods to overcome the growing stream of biomass and waste at a distinct and organisational scale.

Biofilm application in the microbial biochemicals production process

Biofilms can be naturally formed through the attachment of microorganisms on the supporting materials. However, natural biofilms formed in the environment may cause some detrimental effects, such as the equipment contamination and food safety issues et al. On the contrary, biofilms mediated microbial fermentation provides a promising approach for the efficient biochemicals production owing to the properties of self-immobilization, high resistance to toxic reactants and maintenance of long-term cells activity. While few reviews have specifically addressed the biological application of biofilms in the microbial fermentation process. Accordingly, this review will comprehensively summarize the biofilms formation mechanism and potential functions in the microbial fermentation process. Furthermore, the construction strategies for the formation of stable biofilms through synthetic biology technology or the modification of suitable supporting materials will be also discussed. The application of biofilms mediated fermentation will provide an outlook for the biorefinery platform in the future.

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.

Microbial engineering for the production of C2-C6 organic acids

Covering: up to the end of 2020Organic acids, as building block compounds, have been widely used in food, pharmaceutical, plastic, and chemical industries. Until now, chemical synthesis is still the primary method for industrial-scale organic acid production. However, this process encounters some inevitable challenges, such as depletable petroleum resources, harsh reaction conditions and complex downstream processes. To solve these problems, microbial cell factories provide a promising approach for achieving the sustainable production of organic acids. However, some key metabolites in central carbon metabolism are strictly regulated by the network of cellular metabolism, resulting in the low productivity of organic acids. Thus, multiple metabolic engineering strategies have been developed to reprogram microbial cell factories to produce organic acids, including monocarboxylic acids, hydroxy carboxylic acids, amino carboxylic acids, dicarboxylic acids and monomeric units for polymers. These strategies mainly center on improving the catalytic efficiency of the enzymes to increase the conversion rate, balancing the multi-gene biosynthetic pathways to reduce the byproduct formation, strengthening the metabolic flux to promote the product biosynthesis, optimizing the metabolic network to adapt the environmental conditions and enhancing substrate utilization to broaden the substrate spectrum. Here, we describe the recent advances in producing C₂-C₆ organic acids by metabolic engineering strategies. In addition, we provide new insights as to when, what and how these strategies should be taken. Future challenges are also discussed in further advancing microbial engineering and establishing efficient biorefineries.

Mahua flowers (Madhuca sp.) utilization as a carbon-rich natural substrate for the cost-effective bench-scale production of fumaric acid

Fumaric acid is a multi-functional bio-based organic acid that is extensively used as a building block compound in chemical synthesis, food preservative and as therapeutics. The substrates required for the production are the sugars that account for 50–60% of the total process economics. The present work explores the utilization of Mahua flowers as a cheaper carbon source and low cost production medium for cost-effective fumaric acid production using Rhizopus oryzae. Various process parameters for fumaric acid production and desired fungal morphology were investigated, including Mahua flower extract concentration, fermentation temperature, fermentation pH and agitation speed. The highest concentration of the product, fumaric acid obtained in shake flask was 23.5 ± 0.9 g/L at optimized conditions of 100 g/L of Mahua flower extract medium, pH 6, 30 ℃ temperature and shaking speed of 200 rpm in 72 h. The pellet morphology resulted in higher production than mycelial clumps. Bench-scale production in stirred tank reactor resulted in 24.1 ± 1.0 g/L of fumaric acid production at an aeration rate of 1 vvm, agitation at 200 rpm and temperature of 30 ℃. The results obtained were comparable to fermentation with pure glucose. The present study evidently reveals the feasibility of carbon-rich, low cost, abundantly available natural substrate for cost-effective fumaric acid production.

Kinetic Modelling of the Coproduction Process of Fumaric and Malic Acids by Rhizopus arrhizus NRRL 1526

The production of organic acids by biotechnological processes has experienced a notable impulse with the advent of first and second generation biorefineries and the need of searching for renewable and sustainable feedstock, such as biomass. Fumaric acid is a promising biomonomer for polyamide production and a well-known acidulant and preservative in food and feed industries. Malic acid is a well-known food acidulant with a high market share. The biotechnological Fumaric and Malic acid production via fungi of the Rhizopus genus is being explored nowadays as a process for the valorization of food and food-related waste to obtain food ingredients and key platform chemicals of the so-called biochemical biorefinery. In this work, a preliminary study is performed to find reproducible conditions for the production of the acids by Rhizopus arrhizus NRRL 1526 by controlling fungi morphology and inoculum conditions. Afterwards, several production runs are performed to obtain biomass, glucose, and acid concentration data at different processing time values. Finally, an unstructured, unsegregated model including a logistic-type equation for biomass and potential-type equations for the substrate and the products is fitted to experimental data. We find that the production of the organic acids is mainly non-associated with fungal growth.

Electro-membrane processes for organic acid recovery

With an increase in the organic acid requirement, the production of organic acids has been increased over the years. To achieve cost-effective production of organic acids, efficient recovery processes are needed. Electro-membrane processes, including electrodialysis (ED), electrometathesis (EMT), electro-ion substitution (EIS), electro-electrodialysis (EED), electrodialysis with bipolar membrane (EDBM), and electrodeionization (EDI), are promising technologies for the recovery of organic acids. In the electro-membrane processes, organic acids are separated from water and other impurities based on the electro-migration of ions through ion-exchange membranes. These processes can recover various types of organic acids from the fermentation broth with high recovery yield and low energy consumption. In addition, the integration of fermentation and the electro-membrane process can improve the acid recovery with lower byproduct concentration and energy consumption.

With an increase in the organic acid requirement, the publication of organic acids recovery has been increased over the years.

Fumaric acid: production and separation

Fumaric acid is a valuable compound used in foods, beverages, detergents, animal feed, pharmaceuticals and miscellaneous industrial products. It is produced on a large scale by the petrochemical route but the current tendency is towards implementing "green production" and environmental friendly technologies like biotechnological production of fumaric acid using low-cost raw materials. In this context, numerous studies focus on improving the fermentation process not only by using renewable raw material and genetically modified microorganisms, but also by developing and applying different downstream techniques for easy recovery of fumaric acid from the fermented broth. This review presents the main methods for production and separation of fumaric acid, highlighting the advantages and disadvantages of these and the potential economic impact in industry.

Engineered Microorganisms for the Production of Food Additives Approved by the European Union-A Systematic Analysis

In the 1950s, the idea of a single harmonized list of food additives for the European Union arose. Already in 1962, the E-classification system, a robust food safety system intended to protect consumers from possible food-related risks, was introduced. Initially, it was restricted to colorants, but at later stages also preservatives, antioxidants, emulsifiers, stabilizers, thickeners, gelling agents, sweeteners, and flavorings were included. Currently, the list of substances authorized by the European Food Safety Authority (EFSA) (referred to as "E numbers") comprises 316 natural or artificial substances including small organic molecules, metals, salts, but also more complex compounds such as plant extracts and polymers. Low overall concentrations of such compounds in natural producers due to inherent regulation mechanisms or production processes based on non-regenerative carbon sources led to an increasing interest in establishing more reliable and sustainable production platforms. In this context, microorganisms have received significant attention as alternative sources providing access to these compounds. Scientific advancements in the fields of molecular biology and genetic engineering opened the door toward using engineered microorganisms for overproduction of metabolites of their carbon metabolism such as carboxylic acids and amino acids. In addition, entire pathways, e.g., of plant origin, were functionally introduced into microorganisms, which holds the promise to get access to an even broader range of accessible products. The aim of this review article is to give a systematic overview on current efforts during construction and application of microbial cell factories for the production of food additives listed in the EU "E numbers" catalog. The review is focused on metabolic engineering strategies of industrially relevant production hosts also discussing current bottlenecks in the underlying metabolic pathways and how they can be addressed in the future.

Production of fumaric acid by immobilized Rhizopus arrhizus RH 7-13-9# on loofah fiber in a stirred-tank reactor

Fumaric acid is an important building-block chemical. The production of fumaric acid by fermentation is possible. Loofah fiber is a natural, biodegradable, renewable polymer material with highly sophisticated and pore structure. This work investigated a new immobilization method using loofah fiber as carrier to produce fumaric acid in a stirred-tank reactor. Compared with other carriers, loofah fiber was proven to be efficiently and successfully used in the reactor. After the optimization process, 20g addition of loofah fiber and 400rpm agitation speed were chosen as the most suitable process conditions. 30.3g/L fumaric acid in the broth as well as 19.16g fumaric acid in the precipitation of solid was achieved, while the yield from glucose reached 0.211g/g. Three batches of fermentation using the same loofah fiber carrier were conducted successfully, which meant it provided a new method to produce fumaric acid in a stirred-tank reactor.

Comparative proteomics of Rhizopus delemar ATCC 20344 unravels the role of amino acid catabolism in fumarate accumulation

The filamentous fungus Rhizopus delemar naturally accumulates relatively high amounts of fumarate. Although the culture conditions that increase fumarate yields are well established, the network underlying the accumulation of fumarate is not yet fully understood. We set out to increase the knowledge about fumarate accumulation in R. delemar. To this end, we combined a transcriptomics and proteomics approach to identify key metabolic pathways involved in fumarate production in R. delemar, and propose that a substantial part of the fumarate accumulated in R. delemar during nitrogen starvation results from the urea cycle due to amino acid catabolism.

Direct fungal fermentation of lignocellulosic biomass into itaconic, fumaric, and malic acids: current and future prospects

Various economic and environmental sustainability concerns as well as consumer preference for bio-based products from natural sources have paved the way for the development and expansion of biorefining technologies. These involve the conversion of renewable biomass feedstock to fuels and chemicals using biological systems as alternatives to petroleum-based products. Filamentous fungi possess an expansive portfolio of products including the multifunctional organic acids itaconic, fumaric, and malic acids that have wide-ranging current applications and potentially addressable markets as platform chemicals. However, current bioprocessing technologies for the production of these compounds are mostly based on submerged fermentation, which necessitates physicochemical pretreatment and hydrolysis of lignocellulose biomass to soluble fermentable sugars in liquid media. This review will focus on current research work on fungal production of itaconic, fumaric, and malic acids and perspectives on the potential application of solid-state fungal cultivation techniques for the consolidated hydrolysis and organic acid fermentation of lignocellulosic biomass.

Production of fumaric acid from L-malic acid by solvent engineering using a recombinant thermostable fumarase from Thermus thermophilus HB8

Currently, fumaric acid is produced by catalytic isomerization of maleic acid in aqueous solutions at low pH. Being petroleum based, requiring catalyst, and producing vast amounts of by-products and wastewater, the production of fumaric acid from renewable resources by a "green" process is increasingly attractive. In an aqueous solution, the reaction equilibrium constant of the fumarase-mediated conversion of L-malic acid to fumaric acid is 1:4.2 (fumaric acid to L-malic acid). To shift the reaction equilibrium to fumaric acid, solvent engineering was carried out by varying hydrophilic solvents and their concentrations. Generally, organic solvents may denature fumarase. Therefore, fumarase from Thermus thermophilus was employed to overcome this problem. Ethylene glycol was found more suitable than other solvents. This fumarase was shown to be more stable in 50% than in 70% ethylene glycol. Therefore, a preparation was carried out in 50% ethylene glycol. Under this condition, 54.7% conversion was observed using fumarase for transforming 1 mmol L-malic acid. After precipitation by adapting the pH, and washing to remove residual solvent and substrate, 27% total yield was obtained with 99% purity. The results demonstrated that the alternative green route to produce bio-based fumaric acid via L-malic acid is feasible and viable.

Process characterization and influence of alternative carbon sources and carbon-to-nitrogen ratio on organic acid production by Aspergillus oryzae DSM1863

L-Malic acid and fumaric acid are C4 dicarboxylic organic acids and considered as promising chemical building blocks. They can be applied as food preservatives and acidulants in rust removal and as polymerization starter units. Molds of the genus Aspergillus are able to produce malic acid in large quantities from glucose and other carbon sources. In order to enhance the production potential of Aspergillus oryzae DSM 1863, production and consumption rates in an established bioreactor batch-process based on glucose were determined. At 35 °C, up to 42 g/L malic acid was produced in a 168-h batch process with fumaric acid as a by-product. In prolonged shaking flask experiments (353 h), the suitability of the alternative carbon sources xylose and glycerol at a carbon-to-nitrogen (C/N) ratio of 200:1 and the influence of different C/N ratios in glucose cultivations were tested. When using glucose, 58.2 g/L malic acid and 4.2 g/L fumaric acid were produced. When applying xylose or glycerol, both organic acids are produced but the formation of malic acid decreased to 45.4 and 39.4 g/L, respectively. Whereas the fumaric acid concentration was not significantly altered when cultivating with xylose (4.5 g/L), it is clearly enhanced by using glycerol (9.3 g/L). When using glucose as a carbon source, an increase or decrease of the C/N ratio did not influence malic acid production but had an enormous influence on fumaric acid production. The highest fumaric acid concentrations were determined at the highest C/N ratio (300:1, 8.44 g/L) and lowest at the lowest C/N ratio (100:1, 0.7 g/L).

Current and future trends for biofilm reactors for fermentation processes

Biofilms in the environment can both cause detrimental and beneficial effects. However, their use in bioreactors provides many advantages including lesser tendencies to develop membrane fouling and lower required capital costs, their higher biomass density and operation stability, contribution to resistance of microorganisms, etc. Biofilm formation occurs naturally by the attachment of microbial cells to the support without use of any chemicals agent in biofilm reactors. Biofilm reactors have been studied and commercially used for waste water treatment and bench and pilot-scale production of value-added products in the past decades. It is important to understand the fundamentals of biofilm formation, physical and chemical properties of a biofilm matrix to run the biofilm reactor at optimum conditions. This review includes the principles of biofilm formation; properties of a biofilm matrix and their roles in the biofilm formation; factors that improve the biofilm formation, such as support materials; advantages and disadvantages of biofilm reactors; and industrial applications of biofilm reactors.

Rational medium optimization based on comparative metabolic profiling analysis to improve fumaric acid production

To rationally guide fumaric acid production improvement, metabolic profiling approach was performed to analyze metabolite changes of Rhizopus oryzae FM19 under different fermentation conditions. A correlation between the metabolic profiling and fumaric acid production was revealed by principal component analysis as well as partial least squares. Citric acid, oxaloacetic acid, 2-oxoglutarate, lactic acid, proline, alanine, valine, leucine were identified to be mainly responsible for the metabolism difference, which were involved in the Embden-Meyerhof-Parnas, tricarboxylic acid cycle, amino acid metabolism and fatty acid metabolism. Through the further analysis of metabolites changes together with the above pathways, exogenous addition strategies were developed, which resulted in 14% increase of fumaric acid (up to 56.5 g/L) and less by-products. These results demonstrated that metabolic profiling analysis could be successfully applied to the rational guidance of medium optimization and the productivity improvement of value-added compounds.

Fumaric acid production in Saccharomyces cerevisiae by in silico aided metabolic engineering

Fumaric acid (FA) is a promising biomass-derived building-block chemical. Bio-based FA production from renewable feedstock is a promising and sustainable alternative to petroleum-based chemical synthesis. Here we report on FA production by direct fermentation using metabolically engineered Saccharomyces cerevisiae with the aid of in silico analysis of a genome-scale metabolic model. First, FUM1 was selected as the target gene on the basis of extensive literature mining. Flux balance analysis (FBA) revealed that FUM1 deletion can lead to FA production and slightly lower growth of S. cerevisiae. The engineered S. cerevisiae strain obtained by deleting FUM1 can produce FA up to a concentration of 610±31 mg L^–1 without any apparent change in growth in fed-batch culture. FT-IR and ¹H and ¹³C NMR spectra confirmed that FA was synthesized by the engineered S. cerevisiae strain. FBA identified pyruvate carboxylase as one of the factors limiting higher FA production. When the RoPYC gene was introduced, S. cerevisiae produced 1134±48 mg L^–1 FA. Furthermore, the final engineered S. cerevisiae strain was able to produce 1675±52 mg L^–1 FA in batch culture when the SFC1 gene encoding a succinate–fumarate transporter was introduced. These results demonstrate that the model shows great predictive capability for metabolic engineering. Moreover, FA production in S. cerevisiae can be efficiently developed with the aid of in silico metabolic engineering.

Metabolic engineering of Rhizopus oryzae: effects of overexpressing pyc and pepc genes on fumaric acid biosynthesis from glucose

Fumaric acid, a dicarboxylic acid used as a food acidulant and in manufacturing synthetic resins, can be produced from glucose in fermentation by Rhizopus oryzae. However, the fumaric acid yield is limited by the co-production of ethanol and other byproducts. To increase fumaric acid production, overexpressing endogenous pyruvate carboxylase (PYC) and exogenous phosphoenolpyruvate carboxylase (PEPC) to increase the carbon flux toward oxaloacetate were investigated. Compared to the wild type, the PYC activity in the pyc transformants increased 56%-83%, whereas pepc transformants exhibited significant PEPC activity (3-6 mU/mg) that was absent in the wild type. Fumaric acid production by the pepc transformant increased 26% (0.78 g/g glucose vs. 0.62 g/g for the wild type). However, the pyc transformants grew poorly and had low fumaric acid yields (<0.05 g/g glucose) due to the formation of large cell pellets that limited oxygen supply and resulted in the accumulation of ethanol with a high yield of 0.13-0.36 g/g glucose. This study is the first attempt to use metabolic engineering to modify the fumaric acid biosynthesis pathway to increase fumaric acid production in R. oryzae.