An Optimized Ustilago maydis for Itaconic Acid Production at Maximal Theoretical Yield

Studying microbial triglyceride production from corn stover saccharides unveils insights into the galactose metabolism of Ustilago maydis

The global demand for plant oil has reached unprecedented levels and is relevant in all industrial sectors. Driven by the growing awareness for environmental issues of traditional plant oils and the need for eco-friendly alternatives, microbial oil emerges as a promising product with significant potential. Harnessing the capabilities of oleaginous microorganisms is an innovative approach for achieving sustainable oil production. To increase economic feasibility, it is crucial to explore feedstocks such as agricultural waste streams as renewable resource for microbial bioprocesses. The fungal model Ustilago maydis is one promising organism in the field of microbial triglyceride production. It has the ability to metabolize a wide variety of carbon sources for cell growth and accumulates high amounts of triglycerides intracellularly. In this study we asked whether this large variety of usable carbon sources can also be utilized for triglyceride production, using corn stover saccharides as a showcase.Our experiments revealed metabolization of the major saccharide building blocks present in corn stover, demonstrating the remarkable potential of U. maydis. The microorganism exhibited the capacity to synthesize triglycerides using the saccharides glucose, fructose, sucrose, xylose, arabinose, and galactose as carbon source. Notably, while galactose has been formerly considered as toxic to U. maydis, we found that the fungus can metabolize this saccharide, albeit with an extended lag phase of around 100 hours. We identified two distinct methods to significantly reduce or even prevent this lag phase, challenging previous assumptions and expanding the understanding of U. maydis metabolism.Our findings suggest that the two tested methods can prevent long lag phases on feedstocks with high galactose content and that U. maydis can produce microbial triglycerides very efficiently on many different carbon sources. Looking forward, exploring the metabolic capabilities of U. maydis on additional polymeric components of corn stover and beyond holds promise for innovative applications, marking a significant step toward environmentally sustainable bioprocessing technologies.

Balancing pH and yield: exploring itaconic acid production in Ustilago cynodontis from an economic perspective

BACKGROUND

Itaconic acid is a promising bio-based building block for the synthesis of polymers, plastics, fibers and other materials. In recent years, Ustilago cynodontis has emerged as an additional itaconate producing non-conventional yeast, mainly due to its high acid tolerance, which significantly reduces saline waste coproduction during fermentation and downstream processing. As a result, this could likely improve the economic viability of the itaconic acid production process with Ustilaginaceae.

RESULTS

In this study, we characterized a previously engineered itaconate hyper-producing Ustilago cynodontis strain in controlled fed-batch fermentations to determine the minimal and optimal pH for itaconate production. Under optimal fermentation conditions, the hyper-producing strain can achieve the theoretical maximal itaconate yield during the production phase in a fermentation at pH 3.6, but at the expense of considerable base addition. Base consumption is strongly reduced at the pH of 2.8, but at cost of production yield, titer, and rate. A techno-economic analysis based on the entire process demonstrated that savings due to an additional decrease in pH control reagents and saline waste costs cannot compensate the yield loss observed at the highly acidic pH value 2.8.

CONCLUSIONS

Overall, this work provides novel data regarding the balancing of yield, titer, and rate in the context of pH, thereby contributing to a better understanding of the itaconic acid production process with Ustilago cynodontis, especially from an economic perspective.

Efficient production of itaconic acid from the single-carbon substrate methanol with engineered Komagataella phaffii

BACKGROUND

Amidst the escalating carbon dioxide levels resulting from fossil fuel consumption, there is a pressing need for sustainable, bio-based alternatives to underpin future global economies. Single-carbon feedstocks, derived from CO2, represent promising substrates for biotechnological applications. Especially, methanol is gaining prominence for bio-production of commodity chemicals.

RESULTS

In this study, we show the potential of Komagataella phaffii as a production platform for itaconic acid using methanol as the carbon source. Successful integration of heterologous genes from Aspergillus terreus (cadA, mttA and mfsA) alongside fine-tuning of the mfsA gene expression, led to promising initial itaconic acid titers of 28 g·L-1 after 5 days of fed-batch cultivation. Through the combined efforts of process optimization and strain engineering strategies, we further boosted the itaconic acid production reaching titers of 55 g·L-1 after less than 5 days of methanol feed, while increasing the product yield on methanol from 0.06 g·g-1 to 0.24 g·g-1.

CONCLUSION

Our results highlight the potential of K. phaffii as a methanol-based platform organism for sustainable biochemical production.

An Eclectic Review on Dicarboxylic Acid Production Through Yeast Cell Factories and Its Industrial Prominence

Dicarboxylic acid (DCA) is a multifaceted chemical intermediate, recoursed to produce many industrially important products such as adhesives, plasticizers, lubricants, polymers, etc. To bypass the shortcomings of the chemical methods of synthesis of DCA and to reduce fossil fuel footprints, bio-based synthesis is gaining attention. In pursuit of an eco-friendly sustainable alternative method of DCA production, microbial cell factories, and renewable organic resources are gaining popularity. Among the plethora of microbial communities, yeast is being favored industrially compared to bacterial fermentation due to its hyperosmotic and low pH tolerance and flexibility for gene manipulations. By application of rapidly evolving genetic manipulation techniques, the bio-based DCA production could be made more precise and economical. To bridge the gap between supply and demand of DCA, many strategies are employed to improve the fermentation. This review briefly outlines the advancements in DCA production using yeast cell factories with the exemplification of strain improvement strategies.

Exploitation of microbial activities at low pH to enhance planetary health

Awareness is growing that human health cannot be considered in isolation but is inextricably woven with the health of the environment in which we live. It is, however, under-recognized that the sustainability of human activities strongly relies on preserving the equilibrium of the microbial communities living in/on/around us. Microbial metabolic activities are instrumental for production, functionalization, processing, and preservation of food. For circular economy, microbial metabolism would be exploited to produce building blocks for the chemical industry, to achieve effective crop protection, agri-food waste revalorization, or biofuel production, as well as in bioremediation and bioaugmentation of contaminated areas. Low pH is undoubtedly a key physical-chemical parameter that needs to be considered for exploiting the powerful microbial metabolic arsenal. Deviation from optimal pH conditions has profound effects on shaping the microbial communities responsible for carrying out essential processes. Furthermore, novel strategies to combat contaminations and infections by pathogens rely on microbial-derived acidic molecules that suppress/inhibit their growth. Herein, we present the state-of-the-art of the knowledge on the impact of acidic pH in many applied areas and how this knowledge can guide us to use the immense arsenal of microbial metabolic activities for their more impactful exploitation in a Planetary Health perspective.

In situ adsorption of itaconic acid from fermentations of Ustilago cynodontis improves bioprocess efficiency

BACKGROUND

Reducing the costs of biorefinery processes is a crucial step in replacing petrochemical products by sustainable, biotechnological alternatives. Substrate costs and downstream processing present large potential for improvement of cost efficiency. The implementation of in situ adsorption as an energy-efficient product recovery method can reduce costs in both areas. While selective product separation is possible at ambient conditions, yield-limiting effects, as for example product inhibition, can be reduced in an integrated process.

RESULTS

An in situ adsorption process was integrated into the production of itaconic acid with Ustilago cynodontis IAmax, as an example of a promising biorefinery process. A suitable feed strategy was developed to enable efficient production and selective recovery of itaconic acid by maintaining optimal glucose concentrations. Online monitoring via Raman spectroscopy was implemented to enable a first process control and understand the interactions of metabolites with the adsorbent. In the final, integrated bioprocess, yield, titre, and space-time yield of the fermentation process were increased to values of 0.41 gIA/gGlucose, 126.5 gIA/L and 0.52 gIA/L/h. This corresponds to an increase of up to 30% in comparison to the first extended batch experiment without in situ product removal. Itaconic acid was recovered with a purity of at least 95% and high concentrations above 300 g/L in the eluate.

CONCLUSION

Integration of product separation via adsorption into the bioprocess was successfully conducted and improved the efficiency of itaconic acid production. Raman spectroscopy was proven to be a reliable tool for online monitoring of various metabolites and facilitated design and validation of the complex separation and feed process. The general process concept can be transferred to the production of various similar bioproducts, expanding the tool kit for design of innovative biorefinery processes.

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.

Effect of different metabolic pathways on itaconic acid production in engineered Corynebacterium glutamicum

Itaconic acid (IA), a C5-dicarboxylic acid, is a potential bio-based building block for the polymer industry. There are three pathways for IA production from natural IA producers; however, most of the engineered strains were used for IA production by heterologous expression of cis-aconitate decarboxylase gene (cadA) from Aspergillus terreus. In this study, IA was produced by an engineered Corynebacterium glutamicum ATCC 13032 expressing two different types of genes from two distinct pathways. The first involves the mammalian immunoresponsive gene1 (Irg1) derived from Mus musculus. The second (termed here the trans-pathway) involves two genes from the natural IA producer Ustilago maydis which are aconitate-delta-isomerase (Adi1) and trans-aconitate decarboxylase (Tad1) genes. The constructed strains developing the two distinct IA production pathways: C. glutamicum ATCC 13032 pCH-Irg1_opt and C. glutamicum ATCC 13032 pCH-Tad1_optadi1_opt were used for production of IA from different carbon sources. The results reflect the possibility for IA production from C. glutamicum expressing the trans-pathway (Adi1/Tad1 genes) and cis-pathway (Irg1 gene) other than the well-known cis-pathway that depends mainly on cadA gene from A. terreus. The developed strain expressing trans-pathway from U. maydis; however, proved to be better at IA production with high titers of 12.25, 11.34, and 11.02 g/L, and a molar yield of 0.22, 0.42, and 0.43 mol/mol from glucose, maltose, and sucrose, respectively, via fed-batch fermentation. The present study suggests that trans-pathway is better than cis-pathway for IA production in engineered C. glutamicum.

Microbial itaconic acid bioproduction towards sustainable development: Insights, challenges, and prospects

Microbial biomanufacturing is a promising approach to produce high-value compounds with low-carbon footprint and significant economic benefits. Among twelve "Top Value-Added Chemicals from Biomass", itaconic acid (IA) stands out as a versatile platform chemical with numerous applications. IA is naturally produced by Aspergillus and Ustilago species through a cascade enzymatic reaction between aconitase (EC 4.2.1.3) and cis-aconitic acid decarboxylase (EC 4.1.1.6). Recently, non-native hosts such as Escherichia coli, Corynebacterium glutamicum, Saccharomyces cerevisiae, and Yarrowia lipolytica have been genetically engineered to produce IA through the introduction of key enzymes. This review provides an up-to-date summary of the progress made in IA bioproduction, from native to engineered hosts, covers in vivo and in vitro approaches, and highlights the prospects of combination tactics. Current challenges and recent endeavors are also addressed to envision comprehensive strategies for renewable IA production in the future towards sustainable development goals (SDGs).

Renewable carbon sources to biochemicals and -fuels: contributions of the smut fungi Ustilaginaceae

The global demand for food, fuels, and chemicals increases annually. Using renewable C-sources (i.e. biomass, CO₂, and organic waste) is a prerequisite for a future free of fossil carbon. The smut fungi Ustilaginaceae naturally produce a versatile spectrum of valuable products, such as organic acids, polyols, and glycolipids, applicable in the food, energy, chemistry, and pharmaceutical sector. Combined with the use of alternative (co-)substrates (e.g. acetate, butanediol, formate, and glycerol), these microorganisms offer excellent potential for industrial biotechnology, thereby overcoming central challenges humankind faces, including CO₂ release and land use. Here, we provide insight into fundamental production capacities, present genetic modifications that improve the biotechnical application, and review recent high-performance engineering of Ustilaginaceae toward relevant platform chemicals.

Engineering of non-model eukaryotes for bioenergy and biochemical production

The prospect of leveraging naturally occurring phenotypes to overcome bottlenecks constraining the bioeconomy has marshalled increased exploration of nonconventional organisms. This review discusses the status of non-model eukaryotic species in bioproduction, the evaluation criteria for effectively matching a candidate host to a biosynthetic process, and the genetic engineering tools needed for host domestication. We present breakthroughs in genome editing and heterologous pathway design, delving into innovative spatiotemporal modulation strategies that potentiate more refined engineering capabilities. We cover current understanding of genetic instability and its ramifications for industrial scale-up, highlighting key factors and possible remedies. Finally, we propose future opportunities to expand the current collection of available hosts and provide guidance to benefit the broader bioeconomy.

Characterization and engineering of branched short-chain dicarboxylate metabolism in Pseudomonas reveals resistance to fungal 2-hydroxyparaconate

In recent years branched short-chain dicarboxylates (BSCD) such as itaconic acid gained increasing interest in both medicine and biotechnology. Their use as building blocks for plastics urges for developing microbial upcycling strategies to provide sustainable end-of-life solutions. Furthermore, many BSCD exhibit anti-bacterial properties or exert immunomodulatory effects in macrophages, indicating a medical relevance for this group of molecules. For both of these applications, a detailed understanding of the microbial metabolism of these compounds is essential. In this study, the metabolic pathway of BSCD degradation from Pseudomonas aeruginosa PAO1 was studied in detail by heterologously transferring it to Pseudomonas putida. Heterologous expression of the PA0878-0886 itaconate metabolism gene cluster enabled P. putida KT2440 to metabolize itaconate, (S)- and (R)-methylsuccinate, (S)-citramalate, and mesaconate. The functions of the so far uncharacterized genes PA0879 and PA0881 were revealed and proven to extend the substrate range of the core degradation pathway. Furthermore, the uncharacterized gene PA0880 was discovered to encode a 2-hydroxyparaconate (2-HP) lactonase that catalyzes the cleavage of the itaconate derivative 2-HP to itatartarate. Interestingly, 2-HP was found to inhibit growth of the engineered P. putida on itaconate. All in all, this study extends the substrate range of P. putida to include BSCD for bio-upcycling of high-performance polymers, and also identifies 2-HP as promising candidate for anti-microbial applications.

Recent advances and perspectives on production of value-added organic acids through metabolic engineering

Organic acids are important consumable materials with a wide range of applications in the food, biopolymer and chemical industries. The global consumer organic acids market is estimated to increase to $36.86 billion by 2026. Conventionally, organic acids are produced from the chemical catalysis process with petrochemicals as raw materials, which posts severe environmental concerns and conflicts with our sustainable development goals. Most of the commonly used organic acids can be produced from various organisms. As a state-of-the-art technology, large-scale fermentative production of important organic acids with genetically-modified microbes has become an alternative to the chemical route to meet the market demand. Despite the fact that bio-based organic acid production from renewable cheap feedstock provides a viable solution, low productivity has impeded their industrial-scale application. With our deeper understanding of strain genetics, physiology and the availability of strain engineering tools, new technologies including synthetic biology, various metabolic engineering strategies, omics-based system biology tools, and high throughput screening methods are gradually established to bridge our knowledge gap. And they were further applied to modify the cellular reaction networks of potential microbial hosts and improve the strain performance, which facilitated the commercialization of consumable organic acids. Here we present the recent advances of metabolic engineering strategies to improve the production of important organic acids including fumaric acid, citric acid, itaconic acid, adipic acid, muconic acid, and we also discuss the current challenges and future perspectives on how we can develop a cost-efficient, green and sustainable process to produce these important chemicals from low-cost feedstocks.

Construction of cell factory through combinatorial metabolic engineering for efficient production of itaconic acid

BACKGROUND

Itaconic acid, an unsaturated C5 dicarbonic acid, has significant market demand and prospects. It has numerous biological functions, such as anti-cancer, anti-inflammatory, and anti-oxidative in medicine, and is an essential renewable platform chemical in industry. However, the development of industrial itaconic acid production by Aspergillus terreus, the current standard production strain, is hampered by the unavoidable drawbacks of that species. Developing a highly efficient cell factory is essential for the sustainable and green production of itaconic acid.

RESULTS

This study employed combinatorial engineering strategies to construct Escherichia coli cells to produce itaconic acid efficiently. Two essential genes (cis-aconitate decarboxylase (CAD) encoding gene cadA and aconitase (ACO) encoding gene acn) employed various genetic constructs and plasmid combinations to create 12 recombination E. coli strains to be screened. Among them, E. coli BL-CAC exhibited the highest titer with citrate as substrate, and the induction and reaction conditions were further systematically optimized. Subsequently, employing enzyme evolution to optimize rate-limiting enzyme CAD and synthesizing protein scaffolds to co-localize ACO and CAD were used to improve itaconic acid biosynthesis efficiency. Under the optimized reaction conditions combined with the feeding control strategy, itaconic acid titer reached 398.07 mM (51.79 g/L) of engineered E. coli BL-CAR470E-DS/A-CS cells as a catalyst with the highest specific production of 9.42 g/g_(DCW) among heterologous hosts at 48 h.

CONCLUSIONS

The excellent catalytic performance per unit biomass shows the potential for high-efficiency production of itaconic acid and effective reduction of catalytic cell consumption. This study indicates that it is necessary to continuously explore engineering strategies to develop high-performance cell factories to break through the existing bottleneck and achieve the economical commercial production of itaconic acid.

Alleviating glucose repression and enhancing respiratory capacity to increase itaconic acid production

The Crabtree effect products ethanol and acetic acid can be used for itaconic acid (IA) production in Saccharomyces cerevisiae. However, both the IA synthesis and oxidative phosphorylation pathways were hampered by glucose repression when glucose was used as the substrate. This study aimed to improve IA titer by increasing gene expressions related to glucose derepression without impairing yeast growth on glucose. Engineering the acetyl-CoA synthesis pathway increased the titer of IA to 257 mg/L in a urea-based medium. Instead of entire pathway overexpression, we found that some signaling pathways regulating glucose repression were effective targets to improve IA production and respiratory capacity. As a consequence of the reduced inhibition, IA titer was further increased by knocking out a negative regulator of the mitochondrial retrograde signaling MKS1. SNF1/MIG1 signaling was disturbed by deleting the hexokinase HXK2 or an endoplasmic reticulum membrane protein GSF2. The shaking results showed that XYY286 (BY4741, HO::cadA, Y::Dz.ada, 208a::Mt.acs, Δhxk2, pRS415-cadA, pRS423-aac2) accumulated 535 mg/L IA in 168 h in the YSCGLU medium. qRT-PCR results verified that deletion of MKS1 or HXK2 upregulated the gene expressions of the IA synthesis and respiratory pathways during the growth on glucose.

Metabolic engineering of Corynebacterium glutamicum for acetate-based itaconic acid production

BACKGROUND

Itaconic acid is a promising platform chemical for a bio-based polymer industry. Today, itaconic acid is biotechnologically produced with Aspergillus terreus at industrial scale from sugars. The production of fuels but also of chemicals from food substrates is a dilemma since future processes should rely on carbon sources which do not compete for food or feed. Therefore, the production of chemicals from alternative substrates such as acetate is desirable to develop novel value chains in the bioeconomy.

RESULTS

In this study, Corynebacterium glutamicum ATCC 13032 was engineered to efficiently produce itaconic acid from the non-food substrate acetate. Therefore, we rewired the central carbon and nitrogen metabolism by inactivating the transcriptional regulator RamB, reducing the activity of isocitrate dehydrogenase, deletion of the gdh gene encoding glutamate dehydrogenase and overexpression of cis-aconitate decarboxylase (CAD) from A. terreus optimized for expression in C. glutamicum. The final strain C. glutamicum ΔramB Δgdh IDH^R453C (pEKEx2-malEcad_opt) produced 3.43 ± 0.59 g itaconic acid L^-1 with a product yield of 81 ± 9 mmol mol^-1 during small-scale cultivations in nitrogen-limited minimal medium containing acetate as sole carbon and energy source. Lowering the cultivation temperature from 30 °C to 25 °C improved CAD activity and further increased the titer and product yield to 5.01 ± 0.67 g L^-1 and 116 ± 15 mmol mol^-1, respectively. The latter corresponds to 35% of the theoretical maximum and so far represents the highest product yield for acetate-based itaconic acid production. Further, the optimized strain C. glutamicum ΔramB Δgdh IDH^R453C (pEKEx2-malEcad_opt), produced 3.38 ± 0.28 g itaconic acid L^-1 at 25 °C from an acetate-containing aqueous side-stream of fast pyrolysis.

CONCLUSION

As shown in this study, acetate represents a suitable non-food carbon source for itaconic acid production with C. glutamicum. Tailoring the central carbon and nitrogen metabolism enabled the efficient production of itaconic acid from acetate and therefore this study offers useful design principles to genetically engineer C. glutamicum for other products from acetate.

Ustilago maydis Metabolic Characterization and Growth Quantification with a Genome-Scale Metabolic Model

Ustilago maydis is an important plant pathogen that causes corn smut disease and serves as an effective biotechnological production host. The lack of a comprehensive metabolic overview hinders a full understanding of the organism’s environmental adaptation and a full use of its metabolic potential. Here, we report the first genome-scale metabolic model (GSMM) of Ustilago maydis (iUma22) for the simulation of metabolic activities. iUma22 was reconstructed from sequencing and annotation using PathwayTools, and the biomass equation was derived from literature values and from the codon composition. The final model contains over 25% annotated genes (6909) in the sequenced genome. Substrate utilization was corrected by BIOLOG phenotype arrays, and exponential batch cultivations were used to test growth predictions. The growth data revealed a decrease in glucose uptake rate with rising glucose concentration. A pangenome of four different U. maydis strains highlighted missing metabolic pathways in iUma22. The new model allows for studies of metabolic adaptations to different environmental niches as well as for biotechnological applications.

Seventeen Ustilaginaceae High-Quality Genome Sequences Allow Phylogenomic Analysis and Provide Insights into Secondary Metabolite Synthesis

The family of Ustilaginaceae belongs to the order of Basidiomycetes. Despite their plant pathogenicity causing, e.g., corn smut disease, they are also known as natural producers of value-added chemicals such as extracellular glycolipids, organic acids, and polyols. Here, we present 17 high-quality draft genome sequences (N50 > 1 Mb) combining third-generation nanopore and second-generation Illumina sequencing. The data were analyzed with taxonomical genome-based bioinformatics methods such as Percentage of Conserved Proteins (POCP), Average Nucleotide Identity (ANI), and Average Amino Acid Identity (AAI) analyses indicating that a reclassification of the Ustilaginaceae family might be required. Further, conserved core genes were determined to calculate a phylogenomic core genome tree of the Ustilaginaceae that also supported the results of the other phylogenomic analysis. In addition, to genomic comparisons, secondary metabolite clusters (e.g., itaconic acid, mannosylerythritol lipids, and ustilagic acid) of biotechnological interest were analyzed, whereas the sheer number of clusters did not differ much between species.

State of the Art on the Microbial Production of Industrially Relevant Organic Acids

The industrial relevance of organic acids is high; because of their chemical properties, they can be used as building blocks as well as single-molecule agents with a huge annual market. Organic acid chemical platforms can derive from fossil sources by petrochemical refining processes, but most of them also represent natural metabolites produced by many cells. They are the products, by-products or co-products of many primary metabolic processes of microbial cells. Thanks to the potential of microbial cell factories and to the development of industrial biotechnology, from the last decades of the previous century, the microbial-based production of these molecules has started to approach the market. This was possible because of a joint effort of microbial biotechnologists and biochemical and process engineers that boosted natural production up to the titer, yield and productivity needed to be industrially competitive. More recently, the possibility to utilize renewable residual biomasses as feedstock not only for biofuels, but also for organic acids production is further augmenting the sustainability of their production, in a logic of circular bioeconomy. In this review, we briefly present the latest updates regarding the production of some industrially relevant organic acids (citric fumaric, itaconic, lactic and succinic acid), discussing the challenges and possible future developments of successful production.

Itaconate: an antimicrobial metabolite of macrophages

Itaconate is a conjugated 1,4-dicarboxylate produced by macrophages. This small molecule has recently received increasing attention due to its role in modulating the immune response of macrophages upon exposure to pathogens. Itaconate has also been proposed to play an antimicrobial function; however, this has not been explored as intensively. Consistent with the latter, itaconate is known to show antibacterial activity in vitro and was reported to inhibit isocitrate lyase, an enzyme required for survival of bacterial pathogens in mammalian systems. Recent studies have revealed bacterial growth inhibition under biologically relevant conditions. In addition, an antimicrobial role for itaconate is substantiated by the high concentration of itaconate found in bacteria-containing vacuoles, and by the production of itaconate-degrading enzymes in pathogens such as Salmonella enterica ser. Typhimurium, Pseudomonas aeruginosa, and Yersinia pestis. This review describes the current state of literature in understanding the role of itaconate as an antimicrobial agent in host–pathogen interactions.

Recent advances in lignocellulosic biomass white biotechnology for bioplastics

Lignocellulosic biomass has great potential as an inedible feedstock for bioplastic synthesis, although its use is still limited compared to current edible feedstocks of glucose and starch. This review focuses on recent advances in the production of biopolymers and biomonomers from lignocellulosic feedstocks with downstream processing and chemical polymer syntheses. In microbial production, four routes composed of existing poly (lactic acid) and polyhydroxyalkanoates (PHAs) and the emerging biomonomers of itaconic acid and aromatic compounds were presented to review present challenges and future perspectives, focusing on the use of lignocellulosic feedstocks. Recently, advances in purification technologies decreased the number of processes and their environmental burden. Additionally, the unique structures and high-performance of emerging lignocellulose-based bioplastics have expanded the possibilities for the use of bioplastics. The sequence of processes provides insight into the emerging technologies that are needed for the practical use of bioplastics made from lignocellulosic biomass.

The metabolic potential of plastics as biotechnological carbon sources - Review and targets for the future

The plastic crisis requires drastic measures, especially for the plastics' end-of-life. Mixed plastic fractions are currently difficult to recycle, but microbial metabolism might open new pathways. With new technologies for degradation of plastics to oligo- and monomers, these carbon sources can be used in biotechnology for the upcycling of plastic waste to valuable products, such as bioplastics and biosurfactants. We briefly summarize well-known monomer degradation pathways and computed their theoretical yields for industrially interesting products. With this information in hand, we calculated replacement scenarios of existing fossil-based synthesis routes for the same products. Thereby, we highlight fossil-based products for which plastic monomers might be attractive alternative carbon sources. Notably, not the highest yield of product on substrate of the biochemical route, but rather the (in-)efficiency of the petrochemical routes (i.e., carbon, energy use) determines the potential of biochemical plastic upcycling. Our results might serve as a guide for future metabolic engineering efforts towards a sustainable plastic economy.

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.

Recent Advances in Biotechnological Itaconic Acid Production, and Application for a Sustainable Approach

Intense research has been conducted to produce environmentally friendly biopolymers obtained from renewable feedstock to substitute fossil-based materials. This is an essential aspect for implementing the circular bioeconomy strategy, expressly declared by the European Commission in 2018 in terms of "repair, reuse, and recycling". Competent carbon-neutral alternatives are renewable biomass waste for chemical element production, with proficient recyclability properties. Itaconic acid (IA) is a valuable platform chemical integrated into the first 12 building block compounds the achievement of which is feasible from renewable biomass or bio-wastes (agricultural, food by-products, or municipal organic waste) in conformity with the US Department of Energy. IA is primarily obtained through fermentation with Aspergillus terreus, but nowadays several microorganisms are genetically engineered to produce this organic acid in high quantities and on different substrates. Given its trifunctional structure, IA allows the synthesis of various novel biopolymers, such as drug carriers, intelligent food packaging, antimicrobial biopolymers, hydrogels in water treatment and analysis, and superabsorbent polymers binding agents. In addition, IA shows antimicrobial, anti-inflammatory, and antitumor activity. Moreover, this biopolymer retains qualities like environmental effectiveness, biocompatibility, and sustainability. This manuscript aims to address the production of IA from renewable sources to create a sustainable circular economy in the future. Moreover, being an essential monomer in polymer synthesis it possesses a continuous provocation in the biopolymer chemistry domain and technologies, as defined in the present review.

Perspectives for the application of Ustilaginaceae as biotech cell factories

Basidiomycetes fungi of the family Ustilaginaceae are mainly known as plant pathogens causing smut disease on crops and grasses. However, they are also natural producers of value-added substances like glycolipids, organic acids, polyols, and harbor secretory enzymes with promising hydrolytic activities. These attributes recently evoked increasing interest in their biotechnological exploitation. The corn smut fungus Ustilago maydis is the best characterized member of the Ustilaginaceae. After decades of research in the fields of genetics and plant pathology, a broad method portfolio and detailed knowledge on its biology and biochemistry are available. As a consequence, U. maydis has developed into a versatile model organism not only for fundamental research but also for applied biotechnology. Novel genetic, synthetic biology, and process development approaches have been implemented to engineer yields and product specificity as well as for the expansion of the repertoire of produced substances. Furthermore, research on U. maydis also substantially promoted the interest in other members of the Ustilaginaceae, for which the available tools can be adapted. Here, we review the latest developments in applied research on Ustilaginaceae towards their establishment as future biotech cell factories.