A deficiency of manganese ions in the presence of high sugar concentrations is the critical parameter for achieving high yields of itaconic acid by Aspergillus terreus

Metabolic engineering of Shewanella oneidensis to produce glutamate and itaconic acid

Shewanella oneidensis is a gram-negative bacterium known for its unique respiratory capabilities, which allow it to utilize a wide range of electron acceptors, including solid substrates such as electrodes. For a future combination of chemical production and electro-fermentation, the goal of this study was to expand its product spectrum. S. oneidensis was metabolically engineered to optimize its glutamate production and to enable production of itaconic acid. By deleting the glutamate importer gltS for a reduced glutamate uptake and pckA/ptA to redirect the carbon flux towards the TCA cycle, a ∆3 mutant was created. In combination with the plasmid pG2 carrying the glutamate dehydrogenase gdhA and a specific glutamate exporter NCgl1221 A111V, a 72-fold increase in glutamate concentration compared to the wild type was achieved. Along with overexpression of gdhA and NCgl1221 A111V, the deletion of gltS and pckA/ptA as well as the deletion of all three genes (∆3) was examined for their impact on growth and lactate consumption. This showed that the redirection of the carbon flux towards the TCA cycle is possible. Furthermore, we were able to produce itaconic acid for the first time with a S. oneidensis strain. A titer of 7 mM was achieved after 48 h. This suggests that genetic optimization with an expression vector carrying a cis-aconitate decarboxylase (cadA) and a aconitate hydratase (acnB) along with the proven redirection of the carbon flux to the TCA cycle enabled the production of itaconic acid, a valuable platform chemical used in the production of a variety of products. KEY POINTS: •Heterologous expression of gdhA and NCgl1221_A111V leads to higher glutamate production. •Deletion of ackA/pta redirects carbon flux towards TCA cycle. •Heterologous expression of cadA and acnB enables itaconic acid production.

Itaconic acid production by co-feeding of Ustilago maydis: A combined approach of experimental data, design of experiments, and metabolic modeling

Itaconic acid is a platform chemical with a range of applications in polymer synthesis and is also discussed for biofuel production. While produced in industry from glucose or sucrose, co-feeding of glucose and acetate was recently discussed to increase itaconic acid production by the smut fungus Ustilago maydis. In this study, we investigate the optimal co-feeding conditions by interlocking experimental and computational methods. Flux balance analysis indicates that acetate improves the itaconic acid yield up to a share of 40% acetate on a carbon molar basis. A design of experiment results in the maximum yield of 0.14 itaconic acid per carbon source from 100 g L - 1 $\,\text{g L}{}^{-1}$ glucose and 12 g L - 1 $\,\text{g L}{}^{-1}$ acetate. The yield is improved by around 22% when compared to feeding of glucose as sole carbon source. To further improve the yield, gene deletion targets are discussed that were identified using the metabolic optimization tool OptKnock. The study contributes ideas to reduce land use for biotechnology by incorporating acetate as co-substrate, a C2-carbon source that is potentially derived from carbon dioxide.

Evaluating the potential of semi-continuous itaconic acid fermentation by Aspergillus terreus: operational profile and experiences

Itaconic acid is an important bio-based chemical. The present study aims to evaluate the applicability of semi-continuous fermentation technique for itaconic acid production by Aspergillus terreus. The fermentation is planned to be connected with bipolar membrane electrodialysis unit for acid recovery. This process allows the reuse of residual glucose from the effluent. Our particular attention was focused on the effect of glucose concentration. Two different glucose supplementation strategies were tested: constant glucose concentration in the refilling medium and adjusted glucose concentration in order to maintain a continuously high - 120 g/L - glucose concentration in the fermentor. The itaconic acid titre, yield and productivity for the 24 h time periods between draining/refilling interventions were investigated. The constantly high glucose concentration in the fermentor resulted in doubled biomass formation. The average itaconic acid titre was 32.9 ± 2.7 g/L. The producing strain formed numerous spores during semi-continuous fermentation that germinated continuously. Yield and volumetric productivity showed a periodic pattern during the procedure.

Development of an itaconic acid production process with Ustilaginaceae on alternative feedstocks

BACKGROUND

Currently, Aspergillus terreus is used for the industrial production of itaconic acid. Although, alternative feedstock use in fermentations is crucial for cost-efficient and sustainable itaconic acid production, their utilisation with A. terreus most often requires expensive pretreatment. Ustilaginacea are robust alternatives for itaconic acid production, evading the challenges, including the pretreatment of crude feedstocks regarding reduction of manganese concentration, that A. terreus poses.

RESULTS

In this study, five different Ustilago strains were screened for their growth and production of itaconic acid on defined media. The most promising strains were then used to find a suitable alternative feedstock, based on the local food industry. U. cynodontis ITA Max pH, a highly engineered production strain, was selected to determine the biologically available nitrogen concentration in thick juice and molasses. Based on these findings, thick juice was chosen as feedstock to ensure the necessary nitrogen limitation for itaconic acid production. U. cynodontis ITA Max pH was further characterised regarding osmotolerance and product inhibition and a successful scale-up to a 2 L stirred tank reactor was accomplished. A titer of 106.4 gitaconic acid/L with a theoretical yield of 0.50 gitaconic acid/gsucrose and a space-time yield of 0.72 gitaconic acid/L/h was reached.

CONCLUSIONS

This study demonstrates the utilisation of alternative feedstocks to produce ITA with Ustilaginaceae, without drawbacks in either titer or yield, compared to glucose fermentations.

Metabolic engineering to improve production of 3-hydroxypropionic acid from corn-stover hydrolysate in Aspergillus species

BACKGROUND

Fuels and chemicals derived from non-fossil sources are needed to lessen human impacts on the environment while providing a healthy and growing economy. 3-hydroxypropionic acid (3-HP) is an important chemical building block that can be used for many products. Biosynthesis of 3-HP is possible; however, low production is typically observed in those natural systems. Biosynthetic pathways have been designed to produce 3-HP from a variety of feedstocks in different microorganisms.

RESULTS

In this study, the 3-HP β-alanine pathway consisting of aspartate decarboxylase, β-alanine-pyruvate aminotransferase, and 3-hydroxypropionate dehydrogenase from selected microorganisms were codon optimized for Aspergillus species and placed under the control of constitutive promoters. The pathway was introduced into Aspergillus pseudoterreus and subsequently into Aspergillus niger, and 3-HP production was assessed in both hosts. A. niger produced higher initial 3-HP yields and fewer co-product contaminants and was selected as a suitable host for further engineering. Proteomic and metabolomic analysis of both Aspergillus species during 3-HP production identified genetic targets for improvement of flux toward 3-HP including pyruvate carboxylase, aspartate aminotransferase, malonate semialdehyde dehydrogenase, succinate semialdehyde dehydrogenase, oxaloacetate hydrolase, and a 3-HP transporter. Overexpression of pyruvate carboxylase improved yield in shake-flasks from 0.09 to 0.12 C-mol 3-HP C-mol^-1 glucose in the base strain expressing 12 copies of the β-alanine pathway. Deletion or overexpression of individual target genes in the pyruvate carboxylase overexpression strain improved yield to 0.22 C-mol 3-HP C-mol^-1 glucose after deletion of the major malonate semialdehyde dehydrogenase. Further incorporation of additional β-alanine pathway genes and optimization of culture conditions (sugars, temperature, nitrogen, phosphate, trace elements) for 3-HP production from deacetylated and mechanically refined corn stover hydrolysate improved yield to 0.48 C-mol 3-HP C-mol^-1 sugars and resulted in a final titer of 36.0 g/L 3-HP.

CONCLUSIONS

The results of this study establish A. niger as a host for 3-HP production from a lignocellulosic feedstock in acidic conditions and demonstrates that 3-HP titer and yield can be improved by a broad metabolic engineering strategy involving identification and modification of genes participated in the synthesis of 3-HP and its precursors, degradation of intermediates, and transport of 3-HP across the plasma membrane.

Improved Itaconate Production with Ustilago cynodontis via Co-Metabolism of CO2-Derived Formate

In recent years, it was shown that itaconic acid can be produced from glucose with Ustilago strains at up to maximum theoretical yield. The use of acetate and formate as co-feedstocks can boost the efficiency of itaconate production with Ustilaginaceae wild-type strains by reducing the glucose amount and thus the agricultural land required for the biotechnological production of this chemical. Metabolically engineered strains (U. cynodontis Δfuz7 Δcyp3 ↑P_ria1 and U. cynodontis Δfuz7 Δcyp3 P_etefmttA ↑P_ria1) were applied in itaconate production, obtaining a titer of 56.1 g L^-1 and a yield of 0.55 g_itaconate per g_substrate. Both improved titer and yield (increase of 5.2 g L^-1 and 0.04 g_itaconate per g_substrate, respectively) were achieved when using sodium formate as an auxiliary substrate. By applying the design-of-experiments (DoE) methodology, cultivation parameters (glucose, sodium formate and ammonium chloride concentrations) were optimized, resulting in two empirical models predicting itaconate titer and yield for U. cynodontis Δfuz7 Δcyp3 P_etefmttA ↑P_ria1. Thereby, an almost doubled itaconate titer of 138 g L^-1 was obtained and a yield of 0.62 g_itaconate per g_substrate was reached during confirmation experiments corresponding to 86% of the theoretical maximum. In order to close the carbon cycle by production of the co-feed via a "power-to-X" route, the biphasic Ru-catalysed hydrogenation of CO₂ to formate could be integrated into the bioprocess directly using the obtained aqueous solution of formates as co-feedstock without any purification steps, demonstrating the (bio)compatibility of the two processes.

Itaconic acid production is regulated by LaeA in Aspergillus pseudoterreus

The global regulator LaeA controls secondary metabolism in diverse Aspergillus species. Here we explored its role in regulation of itaconic acid production in Aspergillus pseudoterreus. To understand its role in regulating metabolism, we deleted and overexpressed laeA, and assessed the transcriptome, proteome, and secreted metabolome prior to and during initiation of phosphate limitation induced itaconic acid production. We found that secondary metabolite clusters, including the itaconic acid biosynthetic gene cluster, are regulated by laeA and that laeA is required for high yield production of itaconic acid. Overexpression of LaeA improves itaconic acid yield at the expense of biomass by increasing the expression of key biosynthetic pathway enzymes and attenuating the expression of genes involved in phosphate acquisition and scavenging. Increased yield was observed in optimized conditions as well as conditions containing excess nutrients that may be present in inexpensive sugar containing feedstocks such as excess phosphate or complex nutrient sources. This suggests that global regulators of metabolism may be useful targets for engineering metabolic flux that is robust to environmental heterogeneity.

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The Itaconic acid biosynthetic gene cluster is regulated by laeA.

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LaeA is required for production of itaconic acid.

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Overexpression of laeA attenuates genes involved in phosphate acquisition.

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Global regulator engineering increases robustness of itaconic acid production.

Bioreactor as the root cause of the “manganese effect” during Aspergillus niger citric acid fermentations

High-yield citric acid production by the filamentous Ascomycete fungus Aspergillus niger requires a combination of extreme nutritional conditions, of which maintaining a low manganese (II) ion concentration (<5 μg L⁻¹) is a key feature. Technical-scale production of citric acid predominantly uses stainless-steel tank fermenters, but glass bioreactors used for strain improvement and manufacturing process development also contain stainless steel components, in which manganese is an essential alloying element. We show here that during citric acid fermentations manganese (II) ions were leaching from the bioreactor into the growth media, resulting in altered fungal physiology and morphology, and significant reduction of citric acid yields. The leaching of manganese (II) ions was dependent on the fermentation time, the acidity of the culture broth and the sterilization protocol applied. Manganese (II) ion leaching was partially mitigated by electrochemical polishing of stainless steel components of the bioreactor. High concentrations of manganese (II) ions during early cultivation led to a reduction in citric acid yield. However, the effect of manganese (II) ions on the reduction of citric acid yield diminished towards the second half of the fermentation. Since maintaining low concentrations of manganese (II) ions is costly, the results of this study can potentially be used to modify protocols to reduce the cost of citric acid production.

Cell Catalysis of Citrate to Itaconate by Engineered Halomonas bluephagenesis

Itaconic acid (IA), an important five-carbon unsaturated dicarboxylic acid, is one of the top 12 renewable chemicals with an urgent need to reduce industrial production costs. Halomonas bluephagenesis, which possesses the potential for cost-effective bioproduction of chemicals and organic acids due to its ability to grow under open nonsterile conditions and high tolerance to organic acid salts, was genetically engineered and used to produce IA from citrate by a cell catalytic strategy. Here, two essential genes (cis-aconitate decarboxylase encoding gene cadA and aconitase (ACN) encoding gene acn) were introduced into H. bluephagenesis to construct an IA biosynthesis pathway. Further engineering modifications including coexpression of molecular chaperones GroESL, increasing the copy number of the gene encoding rate-limiting enzyme ACN, and weakening the competing pathway were implemented. Under the optimized condition for the cell catalytic system, the engineered strain TAZI-08 produced 451.45 mM (58.73 g/L) IA from 500 mM citrate, with 93.24% conversion in 36 h and a productivity of 1.63 g/(L h). An intermittent feeding strategy further increased the IA titer to 488.86 mM (63.60 g/L). The IA titer and citrate conversion in H. bluephagenesis are the highest among heterologous hosts reported so far, demonstrating that this strain is a suitable chassis for hyperproduction of IA.

Current Progress in Production of Building-Block Organic Acids by Consolidated Bioprocessing of Lignocellulose

Several organic acids have been indicated among the top value chemicals from biomass. Lignocellulose is among the most attractive feedstocks for biorefining processes owing to its high abundance and low cost. However, its highly complex nature and recalcitrance to biodegradation hinder development of cost-competitive fermentation processes. Here, current progress in development of single-pot fermentation (i.e., consolidated bioprocessing, CBP) of lignocellulosic biomass to high value organic acids will be examined, based on the potential of this approach to dramatically reduce process costs. Different strategies for CBP development will be considered such as: (i) design of microbial consortia consisting of (hemi)cellulolytic and valuable-compound producing strains; (ii) engineering of microorganisms that combine biomass-degrading and high-value compound-producing properties in a single strain. The present review will mainly focus on production of organic acids with application as building block chemicals (e.g., adipic, cis,cis-muconic, fumaric, itaconic, lactic, malic, and succinic acid) since polymer synthesis constitutes the largest sector in the chemical industry. Current research advances will be illustrated together with challenges and perspectives for future investigations. In addition, attention will be dedicated to development of acid tolerant microorganisms, an essential feature for improving titer and productivity of fermentative production of acids.

The Role of Metal Ions in Fungal Organic Acid Accumulation

Organic acid accumulation is probably the best-known example of primary metabolic overflow. Both bacteria and fungi are capable of producing various organic acids in large amounts under certain conditions, but in terms of productivity-and consequently, of commercial importance-fungal platforms are unparalleled. For high product yield, chemical composition of the growth medium is crucial in providing the necessary conditions, of which the concentrations of four of the first-row transition metal elements, manganese (Mn²⁺), iron (Fe²⁺), copper (Cu²⁺) and zinc (Zn²⁺) stand out. In this paper we critically review the biological roles of these ions, the possible biochemical and physiological consequences of their influence on the accumulation of the most important mono-, di- and tricarboxylic as well as sugar acids by fungi, and the metal ion-related aspects of submerged organic acid fermentations, including the necessary instrumental analytics. Since producing conditions are associated with a cell physiology that differs strongly to what is observed under “standard” growth conditions, here we consider papers and patents only in which organic acid accumulation levels achieved at least 60% of the theoretical maximum yield, and the actual trace metal ion concentrations were verified.

Carbon-Source Dependent Interplay of Copper and Manganese Ions Modulates the Morphology and Itaconic Acid Production in Aspergillus terreus

The effects of the interplay of copper(II) and manganese(II) ions on growth, morphology and itaconic acid formation was investigated in a high-producing strain of Aspergillus terreus (NRRL1960), using carbon sources metabolized either mainly via glycolysis (D-glucose, D-fructose) or primarily via the pentose phosphate shunt (D-xylose, L-arabinose). Limiting Mn²⁺ concentration in the culture broth is indispensable to obtain high itaconic acid yields, while in the presence of higher Mn²⁺ concentrations yield decreases and biomass formation is favored. However, this low yield in the presence of high Mn²⁺ ion concentrations can be mitigated by increasing the Cu²⁺ concentration in the medium when D-glucose or D-fructose is the growth substrate, whereas this effect was at best modest during growth on D-xylose or L-arabinose. A. terreus displays a high tolerance to Cu²⁺ which decreased when Mn²⁺ availability became increasingly limiting. Under such conditions biomass formation on D-glucose or D-fructose could be sustained at concentrations up to 250 mg L^–1 Cu²⁺, while on D-xylose- or L-arabinose biomass formation was completely inhibited at 100 mg L^–1. High (>75%) specific molar itaconic acid yields always coincided with an “overflow-associated” morphology, characterized by small compact pellets (<250 μm diameter) and short chains of “yeast-like” cells that exhibit increased diameters relative to the elongated cells in growing filamentous hyphae. At low concentrations (≤1 mg L^–1) of Cu²⁺ ions, manganese deficiency did not prevent filamentous growth. Mycelial- and cellular morphology progressively transformed into the typical overflow-associated one when external Cu²⁺ concentrations increased, irrespective of the available Mn²⁺. Our results indicate that copper ions are relevant for overflow metabolism and should be considered when optimizing itaconic acid fermentation in A. terreus.

Ustilaginaceae Biocatalyst for Co-Metabolism of CO2-Derived Substrates toward Carbon-Neutral Itaconate Production

The family Ustilaginaceae (belonging to the smut fungi) are known for their plant pathogenicity. Despite the fact that these plant diseases cause agricultural yield reduction, smut fungi attracted special attention in the field of industrial biotechnology. Ustilaginaceae show a versatile product spectrum such as organic acids (e.g., itaconate, malate, succinate), polyols (e.g., erythritol, mannitol), and extracellular glycolipids, which are considered value-added chemicals with potential applications in the pharmaceutical, food, and chemical industries. This study focused on itaconate as a platform chemical for the production of resins, plastics, adhesives, and biofuels. During this work, 72 different Ustilaginaceae strains from 36 species were investigated for their ability to (co-) consume the CO₂-derived substrates acetate and formate, potentially contributing toward a carbon-neutral itaconate production. The fungal growth and product spectrum with special interest in itaconate was characterized. Ustilago maydis MB215 and Ustilago rabenhorstiana NBRC 8995 were identified as promising candidates for acetate metabolization whereas Ustilago cynodontis NBRC 7530 was identified as a potential production host using formate as a co-substrate enhancing the itaconate production. Selected strains with the best itaconate production were characterized in more detail in controlled-batch bioreactor experiments confirming the co-substrate utilization. Thus, a proof-of-principle study was performed resulting in the identification and characterization of three promising Ustilaginaceae biocatalyst candidates for carbon-neutral itaconate production contributing to the biotechnological relevance of Ustilaginaceae.

High level production of itaconic acid at low pH by Ustilago maydis with fed-batch fermentation

The metabolically engineered plant pathogen Ustilago maydis MB215 Δcyp3 P_etefria1 has been cultivated to produce more than 80 g/L itaconate in 16 L scale pH and temperature controlled fermentation, in fed-batch mode with two successive feedings. The effect of pH as well as successive rounds of feeding has been quantified via elemental balances. Volumetric itaconic acid productivity gradually decreased with successive glucose feedings with increasing itaconic titers, with nearly constant product yield. Extracellular pH was decreased from 6 down to 3.5 and the fermentation was characterized in specific uptake, production, and growth rates. Notable is that the biomass composition changes significantly from growth phase to itaconic acid production phase, carbon content increases from 42% to around 62%. Despite the gradual decrease in itaconic acid levels with decreasing pH (nearly 50% decrease in itaconic acid at pH 3.5, compared to pH 6), significant itaconate production is still observed at pH 4 (around 63 g/L). Biomass yield remained nearly constant until pH 4. Taken together, these results strongly illustrate the potential of engineered Ustilago maydis in itaconate production at commercial levels.

Consolidated bioprocessing of cellulose to itaconic acid by a co-culture of Trichoderma reesei and Ustilago maydis

BACKGROUND

Itaconic acid is a bio-derived platform chemical with uses ranging from polymer synthesis to biofuel production. The efficient conversion of cellulosic waste streams into itaconic acid could thus enable the sustainable production of a variety of substitutes for fossil oil based products. However, the realization of such a process is currently hindered by an expensive conversion of cellulose into fermentable sugars. Here, we present the stepwise development of a fully consolidated bioprocess (CBP), which is capable of directly converting recalcitrant cellulose into itaconic acid without the need for separate cellulose hydrolysis including the application of commercial cellulases. The process is based on a synthetic microbial consortium of the cellulase producer Trichoderma reesei and the itaconic acid producing yeast Ustilago maydis. A method for process monitoring was developed to estimate cellulose consumption, itaconic acid formation as well as the actual itaconic acid production yield online during co-cultivation.

RESULTS

The efficiency of the process was compared to a simultaneous saccharification and fermentation setup (SSF). Because of the additional substrate consumption of T. reesei in the CBP, the itaconic acid yield was significantly lower in the CBP than in the SSF. In order to increase yield and productivity of itaconic acid in the CBP, the population dynamics was manipulated by varying the inoculation delay between T. reesei and U. maydis. Surprisingly, neither inoculation delay nor inoculation density significantly affected the population development or the CBP performance. Instead, the substrate availability was the most important parameter. U. maydis was only able to grow and to produce itaconic acid when the cellulose concentration and thus, the sugar supply rate, was high. Finally, the metabolic processes during fed-batch CBP were analyzed in depth by online respiration measurements. Thereby, substrate availability was again identified as key factor also controlling itaconic acid yield. In summary, an itaconic acid titer of 34 g/L with a total productivity of up to 0.07 g/L/h and a yield of 0.16 g/g could be reached during fed-batch cultivation.

CONCLUSION

This study demonstrates the feasibility of consortium-based CBP for itaconic acid production and also lays the fundamentals for the development and improvement of similar microbial consortia for cellulose-based organic acid production.

Itaconic acid production from undetoxified enzymatic hydrolysate of bamboo residues using Aspergillus terreus

Itaconic acid (IA) production by fermentation of undetoxified hydrolysate of bamboo residues by Aspergillus terreus was demonstrated. Monosaccharides were obtained by pretreatment and enzymatic hydrolysis of bamboo residues. A. terreus could not grow and synthesize IA in the hydrolysate. The buffer was confirmed to be an inhibitor, and was successfully replaced by deionized water as the suspension, to release equivalent sugar and eliminate the inhibition. Corn steep liquor significantly improved the adaptability of A. terreus to the hydrolysate at 2.0 g/L. The IA titer obtained (19.35 g/L IA) was the highest to be reported for IA production from lignocellulose without detoxification. Simultaneous saccharification and fermentation and fed-batch fermentation increased the titer to 22.43 g/L and 41.54 g/L, respectively. Meanwhile, economic assessment proved that bamboo residues were potential substrates for IA production with economic effectiveness.

Exploring the Brazilian diversity of Aspergillus sp. strains for lovastatin and itaconic acid production

Filamentous fungi are well known for producing secondary metabolites applied in various industrial segments. Among these, lovastatin and itaconic acid, produced by Aspergillus terreus, have applications in the pharmaceutical and chemical industries. Lovastatin is primarily used for the control of hypercholesterolemia, while itaconic acid is a building block for the production of synthetic fibers, coating adhesives, among others. In this study, for the first time, 35 strains of Aspergillus sp. from four Brazilian culture collections were evaluated for lovastatin and itaconic acid production and compared to a reference strain, ATCC 20542. From an initial screening, the strains ATCC 20542, URM 224, URM1876, URM 5061, URM 5254, URM 5256, URM 5650, and URM 5961 were selected for genomic comparison. Among tested strains, the locus corresponding to the lovastatin genomic cluster was assembled, showing that all genes essential for lovastatin biosynthesis were present in producing URM 5961 and URM 5650 strains, with 100% and 98.5% similarity to ATCC 20542, respectively. However, in the no producing URM 1876, URM 224, URM 5254, URM 5061, and URM 5256 strains, this cluster was either fragmented or missing. Among the 35 strains evaluated for itaconic acid production in this study, only three strains had titers above 0.5 g/L, 16 strains had production below 0.5 g/L, and the remaining 18 strains had no production, with the highest production of itaconic acid observed in the URM 5254 strain with 2.2 g/L. The essential genes for itaconic acid production, mttA, cadA msfA were also mapped, where all three genes linked to itaconic acid production were found in a single contig in the assembly of each strain. In contrast to lovastatin loci, there is no correlation between the level of itaconic acid production and genetic polymorphisms in the genes associated with its biosynthesis.

The effects of external Mn2+ concentration on hyphal morphology and citric acid production are mediated primarily by the NRAMP-family transporter DmtA in Aspergillus niger

Background

Citric acid, a commodity product of industrial biotechnology, is produced by fermentation of the filamentous fungus Aspergillus niger. A requirement for high-yield citric acid production is keeping the concentration of Mn²⁺ ions in the medium at or below 5 µg L⁻¹. Understanding manganese metabolism in A. niger is therefore of critical importance to citric acid production. To this end, we investigated transport of Mn²⁺ ions in A. niger NRRL2270.

Results

we identified an A. niger gene (dmtA; NRRL3_07789), predicted to encode a transmembrane protein, with high sequence identity to the yeast manganese transporters Smf1p and Smf2p. Deletion of dmtA in A. niger eliminated the intake of Mn²⁺ at low (5 µg L⁻¹) external Mn²⁺ concentration, and reduced the intake of Mn²⁺ at high (> 100 µg L⁻¹) external Mn²⁺ concentration. Compared to the parent strain, overexpression of dmtA increased Mn²⁺ intake at both low and high external Mn²⁺ concentrations. Cultivation of the parent strain under Mn²⁺ ions limitation conditions (5 µg L⁻¹) reduced germination and led to the formation of stubby, swollen hyphae that formed compact pellets. Deletion of dmtA caused defects in germination and hyphal morphology even in the presence of 100 µg L⁻¹ Mn²⁺, while overexpression of dmtA led to enhanced germination and normal hyphal morphology at limiting Mn²⁺ concentration. Growth of both the parent and the deletion strains under citric acid producing conditions resulted in molar yields (Y_p/s) of citric acid of > 0.8, although the deletion strain produced ~ 30% less biomass. This yield was reduced only by 20% in the presence of 100 µg L⁻¹ Mn²⁺, whereas production by the parent strain was reduced by 60%. The Y_p/s of the overexpressing strain was 17% of that of the parent strain, irrespective of the concentrations of external Mn²⁺.

Conclusions

Our results demonstrate that dmtA is physiologically important in the transport of Mn²⁺ ions in A. niger, and manipulation of its expression modulates citric acid overflow.

Ustilago Rabenhorstiana—An Alternative Natural Itaconic Acid Producer

Itaconic acid is an industrial produced chemical by the sensitive filamentous fungus Aspergillus terreus and can replace petrochemical-based monomers for polymer industry. To produce itaconic acid with alternative renewable substrates, such as lignocellulosic based hydrolysates, a robust microorganism is needed due to varying compositions and impurities. Itaconic acid producing basidiomycetous yeasts of the family Ustilaginaceae provide this required characteristic and the species Ustilago rabenhorstiana was examined in this study. By an optimization of media components, process parameters, and a fed-batch mode with glucose the final titer increased from maximum 33.3 g·L−1 in shake flasks to 50.3 g·L−1 in a bioreactor. Moreover, itaconic acid was produced from different sugar monomers based on renewable feedstocks by U. rabenhorstiana and the robustness against weak acids as sugar degradation products was confirmed. Based on these findings, U. rabenhorstiana has a high potential as alternative natural itaconic acid producer besides the well-known U. maydis and A. terreus.

Process engineering of pH tolerant Ustilago cynodontis for efficient itaconic acid production

Background

Ustilago cynodontis ranks among the relatively unknown itaconate production organisms. In comparison to the well-known and established organisms like Aspergillus terreus and Ustilago maydis, genetic engineering and first optimizations for itaconate production were only recently developed for U. cynodontis, enabling metabolic and morphological engineering of this acid-tolerant organism for efficient itaconate production. These engineered strains were so far mostly characterized in small scale shaken cultures.

Results

In pH-controlled fed-batch experiments an optimum pH of 3.6 could be determined for itaconate production in the morphology-engineered U. cynodontis Δfuz7. With U. cynodontis ∆fuz7^r∆cyp3^rP_etefmttA P_ria1ria1, optimized for itaconate production through the deletion of an itaconate oxidase and overexpression of rate-limiting production steps, titers up to 82.9 ± 0.8 g L⁻¹ were reached in a high-density pulsed fed-batch fermentation at this pH. The use of a constant glucose feed controlled by in-line glucose analysis increased the yield in the production phase to 0.61 g_ITA g_GLC⁻¹, which is 84% of the maximum theoretical pathway yield. Productivity could be improved to a maximum of 1.44 g L⁻¹ h⁻¹ and cell recycling was achieved by repeated-batch application.

Conclusions

Here, we characterize engineered U. cynodontis strains in controlled bioreactors and optimize the fermentation process for itaconate production. The results obtained are discussed in a biotechnological context and show the great potential of U. cynodontis as an itaconate producing host.

Efficient itaconic acid production by Aspergillus terreus: Overcoming the strong inhibitory effect of manganese

Itaconic acid (IA), a building block platform chemical, is produced industrially by Aspergillus terreus utilizing glucose. Lignocellulosic biomass can serve as a low cost source of sugars for IA production. However, the fungus could not produce IA from dilute acid pretreated and enzymatically saccharified wheat straw hydrolyzate even at 100-fold dilution. Furfural, hydroxymethyl furfural and acetic acid were inhibitory, as is typical, but Mn²⁺ was particularly problematic for IA production. It was present in the hydrolyzate at a level that was 230 times over the inhibitory limit (50 ppb). Recently, it was found that PO₄ ^3- limitation decreased the inhibitory effect of Mn²⁺ on IA production. In the present study, a novel medium was developed for production of IA by varying PO₄ ^3- , Fe³⁺ and Cu²⁺ concentrations using response surface methodology, which alleviated the strong inhibitory effect of Mn²⁺ . The new medium contained 0.08 g KH₂ PO₄ , 3 g NH₄ NO₃ , 1 g MgSO₄ ·7H₂ O, 5 g CaCl₂ ·2 H₂ O, 0.83 mg FeCl₃ ·6H₂ O, 8 mg ZnSO₄ ·7H₂ O, and 45 mg CuSO₄ ·5H₂ O per liter. The fungus was able to produce IA very well in the presence of Mn²⁺ up to 100 ppm in the medium. This medium will be extremely useful for IA production in the presence of Mn²⁺ . This is the first report on the development of Mn²⁺ tolerant medium for IA production by A. terreus.

Integrated strain- and process design enable production of 220 g L-1 itaconic acid with Ustilago maydis

BACKGROUND

Itaconic acid is an unsaturated, dicarboxylic acid which finds a wide range of applications in the polymer industry and as a building block for fuels, solvents and pharmaceuticals. Currently, Aspergillus terreus is used for industrial production, with titers above 100 g L-1 depending on the conditions. Besides A. terreus, Ustilago maydis is also a promising itaconic acid production host due to its yeast-like morphology. Recent strain engineering efforts significantly increased the yield, titer and rate of production.

RESULTS

In this study, itaconate production by U. maydis was further increased by integrated strain- and process engineering. Next-generation itaconate hyper-producing strains were generated using CRISPR/Cas9 and FLP/FRT genome editing tools for gene deletion, promoter replacement, and overexpression of genes. The handling and morphology of this engineered strain were improved by deletion of fuz7, which is part of a regulatory cascade that governs morphology and pathogenicity. These strain modifications enabled the development of an efficient fermentation process with in situ product crystallization with CaCO3. This integrated approach resulted in a maximum itaconate titer of 220 g L-1, with a total acid titer of 248 g L-1, which is a significant improvement compared to best published itaconate titers reached with U. maydis and with A. terreus.

CONCLUSION

In this study, itaconic acid production could be enhanced significantly by morphological- and metabolic engineering in combination with process development, yielding the highest titer reported with any microorganism.

Evaluating aeration and stirring effects to improve itaconic acid production from glucose using Aspergillus terreus

The effects of the bioreactor conditions, in particular the mode and intensity of aeration and mixing were studied on itaconic acid (IA) fermentation efficiency by Aspergillus terreus strain from glucose substrate. IA was produced in batch system by systematically varying the oxygen content of the aeration gas (from 21 to 31.5 vol% O₂) and the stirring rate (from 150 to 600 rpm). The data were analyzed kinetically to characterize the behavior of the process, and besides, the performances were evaluated comparatively with the literature. It turned out that the operation of the bioreactor with either the higher inlet O₂ concentration (31.5 vol% O₂) or faster stirring (600 rpm) could enhance biological IA generation the most, resulting in yield and volumetric productivity of 0.31 g IA/g glucose and 0.32 g IA/g glucose and 3.15 g IA/L day and 4.26 g IA/L day, respectively. Overall, the significance of fermentation settings was shown in this work regarding IA production catalyzed by A. terreus and notable advances could be realized by adjusting the aeration and stirring towards an optimal combination.

Metabolic engineering with ATP-citrate lyase and nitrogen source supplementation improves itaconic acid production in Aspergillus niger

BACKGROUND

Bio-based production of organic acids promises to be an attractive alternative for the chemicals industry to substitute petrochemicals as building-block chemicals. In recent years, itaconic acid (IA, methylenesuccinic acid) has been established as a sustainable building-block chemical for the manufacture of various products such as synthetic resins, coatings, and biofuels. The natural IA producer Aspergillus terreus is currently used for industrial IA production; however, the filamentous fungus Aspergillus niger has been suggested to be a more suitable host for this purpose. In our previous report, we communicated the overexpression of a putative cytosolic citrate synthase citB in an A. niger strain carrying the full IA biosynthesis gene cluster from A. terreus, which resulted in the highest final titer reported for A. niger (26.2 g/L IA). In this research, we have attempted to improve this pathway by increasing the cytosolic acetyl-CoA pool. Additionally, we have also performed fermentation optimization by varying the nitrogen source and concentration.

RESULTS

To increase the cytosolic acetyl-CoA pool, we have overexpressed genes acl1 and acl2 that together encode for ATP-citrate lyase (ACL). Metabolic engineering of ACL resulted in improved IA production through an apparent increase in glycolytic flux. Strains that overexpress acl12 show an increased yield, titer and productivity in comparison with parental strain CitB#99. Furthermore, IA fermentation conditions were improved by nitrogen supplementation, which resulted in alkalization of the medium and thereby reducing IA-induced weak-acid stress. In turn, the alkalizing effect of nitrogen supplementation enabled an elongated idiophase and allowed final titers up to 42.7 g/L to be reached at a productivity of 0.18 g/L/h and yield of 0.26 g/g in 10-L bioreactors.

CONCLUSION

Ultimately, this study shows that metabolic engineering of ACL in our rewired IA biosynthesis pathway leads to improved IA production in A. niger due to an increase in glycolytic flux. Furthermore, IA fermentation conditions were improved by nitrogen supplementation that alleviates IA induced weak-acid stress and extends the idiophase.

Manganese Deficiency Is Required for High Itaconic Acid Production From D-Xylose in Aspergillus terreus

Itaconic acid is used as a bio-based, renewable building block in the polymer industry. It is produced by submerged fermentations of the filamentous fungus Aspergillus terreus from molasses or starch, but research over the efficient utilization of non-food, lignocellulosic plant biomass is soaring. The objective of this study was to test whether the application of two key cultivation parameters for obtaining itaconic acid from D-glucose in high yields - Mn2+ ion deficiency and high concentration of the carbon source - would also occur on D-xylose, the principal monomer of lignocellulose. To this end, a carbon and energy balance for itaconic acid formation was established, which is 0.83 moles/mole D-xylose. The effect of Mn2+ ions on itaconic acid formation was indeed similar to that on D-glucose and maximal yields were obtained below 3 μg L-1 Mn2+ ions, which were, however, only 0.63 moles of itaconic acid per mole D-xylose. In contrast to the case on D-glucose, increasing D-xylose concentration over 50 g L-1 did not change the above yield. By-products such as xylitol and α-ketoglutarate were found, but in total they remained below 2% of the concentration of D-xylose. Mass balance of the fermentation with 110 g L-1 D-xylose revealed that >95% of the carbon from D-xylose was accounted as biomass, itaconic acid, and the carbon dioxide released in the last step of itaconic acid biosynthesis. Our data show that the efficiency of biomass formation is the critical parameter for itaconic acid yield from D-xylose under otherwise optimal conditions.

Optimized pH and Its Control Strategy Lead to Enhanced Itaconic Acid Fermentation by Aspergillus terreus on Glucose Substrate

Biological itaconic acid production can by catalyzed by Aspergillus terreus (a filamentous fungi) where the fermentation medium pH is of prominent importance. Therefore, in this work, we investigated what benefits the different pH regulation options might offer in enhancing the process. The batch itaconic acid fermentation data underwent a kinetic analysis and the pH control alternatives were ranked subsequently. It would appear that the pH-shift strategy (initial adjustment of pH to 3 and its maintenance at 2.5 after 48 h) resulted in the most attractive fermentation pattern and could hence be recommended to achieve itaconic acid production with an improved performance using A. terreus from carbohydrate, such as glucose. Under this condition, the itaconic acid titer potential, the maximal itaconic acid (titer) production rate, the length of lag-phase and itaconic acid yield were 87.32 g/L, 0.22 g/L/h, 56.04 h and 0.35 g/g glucose, respectively.

Citric acid and itaconic acid accumulation: variations of the same story?

Citric acid production by Aspergillus niger and itaconic acid production by Aspergillus terreus are two major examples of technical scale fungal fermentations based on metabolic overflow of primary metabolism. Both organic acids are formed by the same metabolic pathway, but whereas citric acid is the end product in A. niger, A. terreus performs two additional enzymatic steps leading to itaconic acid. Despite of this high similarity, the optimization of the production process and the mechanism and regulation of overflow of these two acids has mostly been investigated independently, thereby ignoring respective knowledge from the other. In this review, we will highlight where the similarities and the real differences of these two processes occur, which involves various aspects of medium composition, metabolic regulation and compartmentation, transcriptional regulation, and gene evolution. These comparative data may facilitate further investigations of citric acid and itaconic acid accumulation and may contribute to improvements in their industrial production.

Itaconic acid degradation in Aspergillus niger: the role of unexpected bioconversion pathways

BACKGROUND

Itaconic acid (IA), a C5-dicarboxylic acid, has previously been identified as one of the top twelve biochemicals that can be produced by biotechnological means. IA is naturally produced by Aspergillus terreus, however, heterologous production in the related species Aspergillus niger has been proposed earlier. Remarkably, we observed that during high producing conditions and elevated titers A. niger detoxifies the extracellular medium of IA. In order to determine the genes responsible for this decline in IA titers a transcriptome analysis was performed.

RESULTS

Transcriptome analysis has led to the identification of two novel and previously unknown IA bioconversion pathways in A. niger. One pathway is proposed to convert IA into pyruvate and acetyl-CoA through the action of itaconyl-CoA transferase (IctA), itaconyl-CoA hydratase (IchA) and citramalyl-CoA lyase, similar to the pathway identified in A. terreus. Another pathway putatively converts IA into 1-methyl itaconate through the action of trans-aconitate methyltransferase (TmtA). Upon deleting the key genes ictA and ichA we have observed increased IA production and titers and cessation of IA bioconversion. Surprisingly, deletion of tmtA lead to strong reduction of heterologous IA production.

CONCLUSION

Heterologous IA production in A. niger induces the expression of IA bioconversion pathways. These pathways can be inhibited by deleting the key genes ictA, ichA and tmtA. Deletion of ictA and ichA resulted in increased IA production. Deletion of tmtA, however, resulted in almost complete cessation of IA production.

From beech wood to itaconic acid: case study on biorefinery process integration

Renewable raw materials in sustainable biorefinery processes pose new challenges to the manufacturing routes of platform chemicals. Beside the investigations of individual unit operations, the research on process chains, leading from plant biomass to the final products like lactic acid, succinic acid, and itaconic acid is increasing. This article presents a complete process chain from wooden biomass to the platform chemical itaconic acid. The process starts with the mechanical pretreatment of beech wood, which subsequently is subjected to chemo-catalytic biomass fractionation (OrganoCat) into three phases, which comprise cellulose pulp, aqueous hydrolyzed hemicellulose, and organic lignin solutions. Lignin is transferred to further chemical valorization. The aqueous phase containing oxalic acid as well as hemi-cellulosic sugars is treated by nanofiltration to recycle the acid catalyst back to the chemo-catalytic pretreatment and to concentrate the sugar hydrolysate. In a parallel step, the cellulose pulp is enzymatically hydrolyzed to yield glucose, which-together with the pentose-rich stream-can be used as a carbon source in the fermentation. The fermentation of the sugar fraction into itaconic acid can either be performed with the established fungi Aspergillus terreus or with Ustilago maydis. Both fermentation concepts were realized and evaluated. For purification, (in situ) filtration, (in situ) extraction, and crystallization were investigated. The presented comprehensive examination and discussion of the itaconate synthesis process-as a case study-demonstrates the impact of realistic process conditions on product yield, choice of whole cell catalyst, chemocatalysts and organic solvent system, operation mode, and, finally, the selection of a downstream concept.

High oxygen tension increases itaconic acid accumulation, glucose consumption, and the expression and activity of alternative oxidase in Aspergillus terreus

Itaconic acid is a five-carbon dicarboxylic acid with an unsaturated alkene bond, frequently used as a building block for the industrial production of a variety of synthetic polymers. It is also one of the major products of fungal "overflow metabolism" which can be produced in submerged fermentations of the filamentous fungus Aspergillus terreus. At the present, molar yields of itaconate are lower than those obtained in citric acid production in Aspergillus niger. Here, we have studied the possibility that the yield may be limited by the oxygen supply during fermentation and hence tested the effect of the dissolved oxygen concentration on the itaconic acid formation rate and yield in lab-scale bioreactors. The data show that a dissolved oxygen concentration of 2% saturation was sufficient for maximal biomass formation. Raising it to 30% saturation had no effect on biomass formation or the growth rate, but the itaconate yield augmented substantially from 0.53 to 0.85 mol itaconate/mol glucose. Furthermore, the volumetric and specific rates of itaconic acid formation ameliorated by as much as 150% concurrent with faster glucose consumption, shortening the fermentation time by 48 h. Further increasing the dissolved oxygen concentration over 30% saturation had no effect. Moreover, we show that this increase in itaconic acid production coincides with an increase in alternative respiration, circumventing the formation of surplus ATP by the cytochrome electron transport chain, as well as with increased levels of alternative oxidase transcript. We conclude that high(er) itaconic acid accumulation requires a dissolved oxygen concentration that is much higher than that needed for maximal biomass formation, and postulate that the induction of alternative respiration allows the necessary NADH reoxidation ratio without surplus ATP production to increase the glucose consumption and the flux through overflow metabolism.

Factors Affecting Production of Itaconic Acid from Mixed Sugars by Aspergillus terreus

Itaconic acid (IA; a building block platform chemical) is currently produced industrially from glucose by fermentation with Aspergillus terreus. In order to expand the use of IA, its production cost must be lowered. Lignocellulosic biomass has the potential to serve as low-cost source of sugars for IA production. It was found that the fungus cannot produce IA from dilute acid pretreated and enzymatically saccharified wheat straw hydrolysate even at 100-fold dilution. The effects of typical compounds (acetic acid, furfural, HMF and Mn²⁺, enzymes, CaSO₄), culture conditions (initial pH, temperature, aeration), and medium components (KH₂PO₄, NH₄NO₃, CaCl₂·2H₂O, FeCl₃·6H₂O) on growth and IA production by A. terreus NRRL 1972 using mixed sugar substrate containing glucose, xylose, and arabinose (4:3:1, 80 g L^-1) mimicking the wheat straw hydrolysate were investigated. Acetic acid, furfural, Mn²⁺, and enzymes were strong inhibitors to both growth and IA production from mixed sugars. Optimum culture conditions (pH 3.1, 33 °C, 200 rpm) and medium components (0.8 g KH₂PO₄, 3 g NH₄NO₃, 2.0 g CaCl₂·2H₂O, 0.83-3.33 mg FeCl₃·6H₂O per L) as well as tolerable levels of inhibitors (0.4 g acetic acid, < 0.1 g furfural, 100 mg HMF, < 5.0 ppb Mn²⁺, 24 mg CaSO₄ per L) for mixed sugar utilization were established. The results will be highly useful for developing a bioprocess technology for IA production from lignocellulosic feedstocks.

World market and biotechnological production of itaconic acid

The itaconic acid (IA) world market is expected to exceed 216 million of dollars by 2020 as a result of an increasing demand for bio-based chemicals. The potential of this organic acid produced by fermentation mainly with filamentous fungi relies on the vast industrial applications of polymers derived from it. The applications may be as a superabsorbent polymer for personal care or agriculture, unsaturated polyester resin for the transportation industry, poly(methyl methacrylate) for electronic devices, among many others. However, the existence of other substitutes and the high production cost limit the current IA market. IA manufacturing is done mainly in China and other Asia-Pacific countries. Higher economic feasibility and production worldwide may be achieved with the use of low-cost feedstock of local origin and with the development of applications targeted to specific local markets. Moreover, research on the biological pathway for IA synthesis and the effect of medium composition are important for amplifying the knowledge about the production of that biochemical with great market potential.

Production of itaconic acid by biotransformation of wheat bran hydrolysate with Aspergillus terreus CICC40205 mutant

The replacement of the carbon source in the microbial production of itaconic acid (IA) with economic alternatives has attracted significant attention. In this study, an Aspergillus terreus CICC40205 mutant was used to increase the IA titer and decrease the citric acid titer in the wheat bran hydrolysate compared with the parental strain. The results showed that the IA titer was increased by 33.4%, whereas the citric acid titer was decreased by 75.8%, and were in accordance with those of the improved pathway of co-metabolism of glucose and xylose according to the metabolic flux analysis. Additionally, the maximum IA titer obtained in a 7-L stirred tank was 49.65gL^-1±0.38gL^-1. Overall, A. terreus CICC40205 showed a great potential for the industrial production of IA through the biotransformation of the wheat bran hydrolysate.

Process relevant screening of cellulolytic organisms for consolidated bioprocessing

BACKGROUND

Although the biocatalytic conversion of cellulosic biomass could replace fossil oil for the production of various compounds, it is often not economically viable due to the high costs of cellulolytic enzymes. One possibility to reduce costs is consolidated bioprocessing (CBP), integrating cellulase production, hydrolysis of cellulose, and the fermentation of the released sugars to the desired product into one process step. To establish such a process, the most suitable cellulase-producing organism has to be identified. Thereby, it is crucial to evaluate the candidates under target process conditions. In this work, the chosen model process was the conversion of cellulose to the platform chemical itaconic acid by a mixed culture of a cellulolytic fungus with Aspergillus terreus as itaconic acid producer. Various cellulase producers were analyzed by the introduced freeze assay that measures the initial carbon release rate, quantifying initial cellulase activity under target process conditions. Promising candidates were then characterized online by monitoring their respiration activity metabolizing cellulose to assess the growth and enzyme production dynamics.

RESULTS

The screening of five different cellulase producers with the freeze assay identified Trichoderma reesei and Penicillium verruculosum as most promising. The measurement of the respiration activity revealed a retarded induction of cellulase production for P. verruculosum but a similar cellulase production rate afterwards, compared to T. reesei. The freeze assay measurement depicted that P. verruculosum reaches the highest initial carbon release rate among all investigated cellulase producers. After a modification of the cultivation procedure, these results were confirmed by the respiration activity measurement. To compare both methods, a correlation between the measured respiration activity and the initial carbon release rate of the freeze assay was introduced. The analysis revealed that the different initial enzyme/cellulose ratios as well as a discrepancy in cellulose digestibility are the main differences between the two approaches.

CONCLUSIONS

With two complementary methods to quantify cellulase activity and the dynamics of cellulase production for CBP applications, T. reesei and P. verruculosum were identified as compatible candidates for the chosen model process. The presented methods can easily be adapted to screen for suitable cellulose degrading organisms for various other applications.

Integrated process development of a reactive extraction concept for itaconic acid and application to a real fermentation broth

Itaconic acid (IA) has a high potential to be used as a bio-based platform chemical and its biocatalytic production via fermentation has significantly improved within the last decade. Additionally downstream processing using reactive extraction (RE) was described, potentially enabling a more efficient sustainable bioprocess producing IA. The bottleneck to overcome is the connection of up- and downstream processing, caused by lack of biocompatibility of the RE systems and direct application to fermentation broth. Within this study, a biocompatible RE system for IA is defined (pH dependency, extraction mechanism) and used for direct application to a fermentation broth. By optimizing the biocatalyst, the production medium, and the extraction system in an integrated approach, it was possible to define critical parameters that enabled a tuning of the overall bioprocess. With an extraction yield of Y _IA = 0.80 ± 0.03, IA could be produced as sole carboxylic acid ( b IA , 0 aq  = 0.490 mol/kg^aq) using a RE system consisting of ethyl oleate as organic solvent and tri-n-octylamine as extractant ( b T - C 8 org  = 0.6 mol/kg^org). This work is a proof of concept and demonstrates that by joint consideration of up- and downstream processing, optimized bioprocesses can be developed.

Emerging biotechnologies for production of itaconic acid and its applications as a platform chemical

Recently, itaconic acid (IA), an unsaturated C5-dicarboxylic acid, has attracted much attention as a biobased building block chemical. It is produced industrially (&gt;80 g L−1) from glucose by fermentation with Aspergillus terreus. The titer is low compared with citric acid production (&gt;200 g L−1). This review summarizes the latest progress on enhancing the yield and productivity of IA production. IA biosynthesis involves the decarboxylation of the TCA cycle intermediate cis-aconitate through the action of cis-aconitate decarboxylase (CAD) enzyme encoded by the CadA gene in A. terreus. A number of recombinant microorganisms have been developed in an effort to overproduce it. IA is used as a monomer for production of superabsorbent polymer, resins, plastics, paints, and synthetic fibers. Its applications as a platform chemical are highlighted. It has a strong potential to replace petroleum-based methylacrylic acid in industry which will create a huge market for IA.

Production of lovastatin and itaconic acid by Aspergillus terreus: a comparative perspective

Aspergillus terreus is a textbook example of an industrially relevant filamentous fungus. It is used for the biotechnological production of two valuable metabolites, namely itaconic acid and lovastatin. Itaconic acid serves as a precursor in polymer industry, whereas lovastatin found its place in the pharmaceutical market as a cholesterol-lowering statin drug and a precursor for semisynthetic statins. Interestingly, their biosynthetic gene clusters were shown to reside in the common genetic neighborhood. Despite the genomic proximity of the underlying biosynthetic genes, the production of lovastatin and itaconic acid was shown to be favored by different factors, especially with respect to pH values of the broth. While there are several reviews on various aspects of lovastatin and itaconic acid production, the survey on growth conditions, biochemistry and morphology related to the formation of these two metabolites has never been presented in the comparative manner. The aim of the current review is to outline the correlations and contrasts with respect to process-related and biochemical discoveries regarding itaconic acid and lovastatin production by A. terreus.