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

Taurine-mediated gene transcription and cell membrane permeability reinforced co-production of bioethanol and Monascus azaphilone pigments for a newly isolated Monascus purpureus

BACKGROUND

Taurine, a semi-essential micronutrient, could be utilized as a sulfur source for some bacteria; however, little is known about its effect on the accumulation of fermentation products. Here, it investigated the effect of taurine on co-production of bioethanol and Monascus azaphilone pigments (MonAzPs) for a fungus.

RESULTS

A newly isolated fungus of 98.92% identity with Monascus purpureus co-produced 23.43 g/L bioethanol and 66.12, 78.01 and 62.37 U/mL red, yellow and orange MonAzPs for 3 d in synthetic medium (SM). Taurine enhanced bioethanol titer, ethanol productivity and ethanol yield at the maximum by 1.56, 1.58 and 1.60 times than those of the control in corn stover hydrolysates (CSH), and red, yellow and orange MonAzPs were raised by 1.24, 1.26 and 1.29 times, respectively. Taurine was consumed extremely small quantities for M. purpureus and its promotional effect was not universal for the other two biorefinery fermenting strains. Taurine intensified the gene transcription of glycolysis (glucokinase, phosphoglycerate mutase, enolase and alcohol dehydrogenase) and MonAzPs biosynthesis (serine hydrolases, C-11-ketoreductase, FAD-dependent monooxygenase, 4-O-acyltransferase, deacetylase, NAD(P)H-dependent oxidoredutase, FAD-dependent oxidoredutase, enoyl reductase and fatty acid synthase) through de novo RNA-Seq assays. Furthermore, taurine improved cell membrane permeability through changing cell membrane structure by microscopic imaging assays.

CONCLUSIONS

Taurine reinforced co-production of bioethanol and MonAzPs by increasing gene transcription level and cell membrane permeability for M. purpureus. This work would offer an innovative, efficient and taurine-based co-production system for mass accumulation of the value-added biofuels and biochemicals from lignocellulosic biomass.

Utilization of sweet sorghum juice as a carbon source for enhancement of itaconic acid production in engineered Corynebacterium glutamicum

Itaconic acid is a promising biochemical building block that can be used in polymer synthesis. Itaconic acid is currently produced in industry by the natural producer fungus Aspergillus terreus using glucose as a main carbon source. Most research for itaconic acid production using lignocellulosic-based carbon sources was carried out by A. terreus. Engineered Corynebacterium glutamicum strain which can grow in presence of fermentation inhibitors without effect on growth, was used for production of itaconic acid using sweet sorghum juice and bagasse sugar lysate (BSL). BSL contains many inhibitors unlike sorghum juice. C. glutamicum could grow in the media containing both types of lignocellulose-based carbon sources without showing any growth inhibition, however, sorghum juice was better in itaconic acid production than BSL. Different constructed strains of C. glutamicum were used for itaconic acid production, however, C. glutamicum ATCC 13032 pCH-Tad1optAdi1opt strain expressing Adi1/Tad1 genes (trans-pathway) from Ustilago maydis proved to be better in itaconic acid production giving final titer of 8.4 and 4.02 g/L using sweet sorghum juice and BSL as the sole carbon sources by fed-batch fermentation. Our study is the first for production of itaconic acid using sweet sorghum juice and BSL. The present study also proved that C. glutamicum can be used for enhancing itaconic acid production using lignocellulosic-based carbon sources.

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).

Enhanced production of itaconic acid from enzymatic hydrolysate of lignocellulosic biomass by recombinant Corynebacteriumglutamicum

Itaconic acid (IA) is a value-added chemical currently produced by Aspergillus terreus from edible glucose and starch but not from inedible lignocellulosic biomass owing to the high sensitivity to fermentation inhibitors present in the hydrolysate of lignocellulosic biomass. To produce IA from lignocellulosic biomass, a gram-positive bacterium, Corynebacterium glutamicum, with a high tolerance to fermentation inhibitors was metabolically engineered to express a fusion protein composed of cis-aconitate decarboxylase from A. terreus responsible for IA formation from cis-aconitate and a maltose-binding protein (malE) from Escherichia coli. The codon-optimized cadA_malE gene was expressed in C. glutamicum ATCC 13032, and the resulting recombinant strain produced IA from glucose. IA concentration increased 4.7-fold by the deletion of the ldh gene encoding lactate dehydrogenase. With the Δldh strain HKC2029, an 18-fold higher IA production was observed from enzymatic hydrolysate of kraft pulp as a model lignocellulosic biomass than from glucose (6.15 and 0.34 g/L, respectively). The enzymatic hydrolysate of kraft pulp contained various potential fermentation inhibitors involved in furan aldehydes, benzaldehydes, benzoic acids, cinnamic acid derivatives, and aliphatic acid. Whereas cinnamic acid derivatives severely inhibited IA production, furan aldehydes, benzoic acids, and aliphatic acid improved IA production at low concentrations. The present study suggests that lignocellulosic hydrolysate contains various potential fermentation inhibitors; however, some of them can serve as enhancers for microbial fermentation likely due to the changing of redox balance in the cell.

Recent Advances on the Production of Itaconic Acid via the Fermentation and Metabolic Engineering

Itaconic acid (ITA) is one of the top 12 platform chemicals. The global ITA market is expanding due to the rising demand for bio-based unsaturated polyester resin and its non-toxic qualities. Although bioconversion using microbes is the main approach in the current industrial production of ITA, ecological production of bio-based ITA faces several issues due to: low production efficiency, the difficulty to employ inexpensive raw materials, and high manufacturing costs. As metabolic engineering advances, the engineering of microorganisms offers a novel strategy for the promotion of ITA bio-production. In this review, the most recent developments in the production of ITA through fermentation and metabolic engineering are compiled from a variety of perspectives, including the identification of the ITA synthesis pathway, the metabolic engineering of natural ITA producers, the design and construction of the ITA synthesis pathway in model chassis, and the creation, as well as application, of new metabolic engineering strategies in ITA production. The challenges encountered in the bio-production of ITA in microbial cell factories are discussed, and some suggestions for future study are also proposed, which it is hoped offers insightful views to promote the cost-efficient and sustainable industrial production of ITA.

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.

Environmental assessment of the production of itaconic acid from wheat straw under a biorefinery approach

This study performs the environmental assessment of itaconic acid (IA) production from wheat straw. The Life Cycle Assessment (LCA) methodology is used to determine the environmental hotspots, considering impact categories such as Global Warming (GW), Fossil Resource Scarcity (FRS), Water Consumption (WC), among others. A sensitivity analysis was performed considering an optimization of the steam explosion process and 100% renewable energy. Results report an impact of about 14.33 kg CO₂ eq in GW, 4.15 kg of oil eq in FRS, for each kg of IA produced for the baseline scenario. Moreover, the pretreatment and fermentation stages constitute hotspots of the IA production. In addition, using a renewable energy source in production would reduce the impact by 82% in GW, 71% in PM and 82% in FRS categories. The optimization of the steam explosion process presents a better performance in GW and FRS but also lies in an increase in WC.

The role of filamentous fungi in advancing the development of a sustainable circular bioeconomy

Human activities generate enormous amounts of organic wastes and residues. Filamentous fungi (FF) are able to grow on a broad range of substrates and survive over a wide spectrum of growth conditions. These characteristics enable FF to be exploited in biorefineries for various waste streams. Valorization of food industry byproducts into biomass and various arrays of value-added products using FF creates promising pathways toward a sustainable circular economy. This approach might also contribute to reaching the sustainable development goals set by the United Nations, particularly for zero hunger as well as affordable and clean energy. This paper presents the application of filamentous fungi in food, feeds, fuels, biochemicals, and biopolymers. The nutritional values, health benefits, and safety of foods derived from byproducts of food industries are also addressed. The technoeconomical feasibilities, sustainability aspects and challenges and future perspectives for biorefineries using filamentous fungi are discussed.

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.

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.

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.

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.

A Sight to Wheat Bran: High Value-Added Products

Recently more consideration has been given to the use of renewable materials and agricultural residues. Wheat production is increasing yearly and correspondingly, the volume of by-products from the wheat process is increasing, as well. It is important to find the use of the residuals for higher value-added products, and not just for the food industry or animal feed purposes as it is happening now. Agricultural residue of the roller milled wheat grain is a wheat bran description. The low-cost of wheat bran and its composition assortment provides a good source of substrate for various enzymes and organic acids production and other biotechnological applications. The main purpose of this review article is to look into recent trends, developments, and applications of wheat bran.

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.

Improved itaconic acid production by Aspergillus niveus using blended algal biomass hydrolysate and glycerol as substrates

Superfluous algal biomass hydrolysate and purified glycerol obtained from biodiesel production were utilized for the production of itaconic acid by Aspergillus niveus. The lipid extracted Gracilaria edulis algal biomass residual was subjected to a pretreatment for the enhanced production of itaconic acid. Glycerol acquired from biodiesel production was pretreated and utilized as a substrate for itaconic acid production. The effect of individual and combined substrate concentration on itaconic acid production was investigated. Ultrasonication combined with the acid pretreated algal biomass produces higher itaconic acid due to the higher level of the total carbohydrate content (58.47 ± 2.57% w/v). After 168 h of incubation, A. niveus utilizes algal biomass hydrolysate and purified glycerol as substrate and produced 31.55 ± 1.25 g/L of itaconic acid and the dry cell weight is 18.24 ± 0.23 g/L respectively. Glycerol and algal biomass hydrolysate was a potential substrate for itaconic acid production by fungal species.

Biomass-Derived Production of Itaconic Acid as a Building Block in Specialty Polymers

Biomass, the only source of renewable organic carbon on Earth, offers an efficient substrate for bio-based organic acid production as an alternative to the leading petrochemical industry based on non-renewable resources. Itaconic acid (IA) is one of the most important organic acids that can be obtained from lignocellulose biomass. IA, a 5-C dicarboxylic acid, is a promising platform chemical with extensive applications; therefore, it is included in the top 12 building block chemicals by the US Department of Energy. Biotechnologically, IA production can take place through fermentation with fungi like Aspergillus terreus and Ustilago maydis strains or with metabolically engineered bacteria like Escherichia coli and Corynebacterium glutamicum. Bio-based IA represents a feasible substitute for petrochemically produced acrylic acid, paints, varnishes, biodegradable polymers, and other different organic compounds. IA and its derivatives, due to their trifunctional structure, support the synthesis of a wide range of innovative polymers through crosslinking, with applications in special hydrogels for water decontamination, targeted drug delivery (especially in cancer treatment), smart nanohydrogels in food applications, coatings, and elastomers. The present review summarizes the latest research regarding major IA production pathways, metabolic engineering procedures, and the synthesis and applications of novel polymeric materials.

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.

Process design and economic analysis of a biorefinery co-producing itaconic acid and electricity from sugarcane bagasse and trash lignocelluloses

Itaconic acid has economic potential as a commodity biochemical for the sugar industry, but its production is limited due to high production costs. Using cheaper and alternative lignocellulosic feedstocks together with achieving higher product titres have been identified as potential strategies for viable IA production. Consequently the use of sugarcane bagasse and trash for the production of itaconic acid (IA) and electricity have been investigated for an integrated biorefinery, where the production facility is annexed to an existing sugar mill and new combined heat and power (CHP) plant. Three IA biorefinery scenarios were designed and simulated in Aspen Plus®. Subsequent economic analyses indicated that cheaper feedstocks reduced the IA production cost from 1565.5 US$/t for glucose to 616.5 US$/t, but coal supplementation was required to sufficiently lower the production cost to 604.3 US$/t for a competitive IA selling price of 1740 US$/t, compared to the market price of 1800 US$/t.

Novel optimization strategy for tannase production through a modified solid-state fermentation system

BACKGROUND

High amounts of insoluble substrates exist in the traditional solid-state fermentation (SSF) system. The presence of these substrates complicates the determination of microbial biomass. Thus, enzyme activity is used as the sole index for the optimization of the traditional SSF system, and the relationship between microbial growth and enzyme synthesis is always ignored. This study was conducted to address this deficiency. All soluble nutrients from tea stalk were extracted using water. The aqueous extract was then mixed with polyurethane sponge to establish a modified SSF system, which was then used to conduct tannase production. With this system, biomass, enzyme activity, and enzyme productivity could be measured rationally and accurately. Thus, the association between biomass and enzyme activity could be easily identified, and the shortcomings of traditional SSF could be addressed.

RESULTS

Different carbon and nitrogen sources exerted different effects on microbial growth and enzyme production. Single-factor experiments showed that glucose and yeast extract greatly improved microbial biomass accumulation and that tannin and (NH₄)₂SO₄ efficiently promoted enzyme productivity. Then, these four factors were optimized through response surface methodology. Tannase activity reached 19.22 U/gds when the added amounts of tannin, glucose, (NH₄)₂SO₄, and yeast extract were 7.49, 8.11, 9.26, and 2.25%, respectively. Tannase activity under the optimized process conditions was 6.36 times higher than that under the initial process conditions. The optimized parameters were directly applied to the traditional tea stalk SSF system. Tannase activity reached 245 U/gds, which is 2.9 times higher than our previously reported value.

CONCLUSIONS

In this study, a modified SSF system was established to address the shortcomings of the traditional SSF system. Analysis revealed that enzymatic activity and microbial biomass are closely related, and different carbon and nitrogen sources have different effects on microbial growth and enzyme production. The maximal tannase activity was obtained under the optimal combination of nutrient sources that enhances cell growth and tannase accumulation. Moreover, tannase production through the traditional tea stalk SSF was markedly improved when the optimized parameters were applied. This work provides an innovative approach to bioproduction research through SSF.

Producing Acetic Acid of Acetobacter pasteurianus by Fermentation Characteristics and Metabolic Flux Analysis

The acetic acid bacterium Acetobacter pasteurianus plays an important role in acetic acid fermentation, which involves oxidation of ethanol to acetic acid through the ethanol respiratory chain under specific conditions. In order to obtain more suitable bacteria for the acetic acid industry, A. pasteurianus JST-S screened in this laboratory was compared with A. pasteurianus CICC 20001, a current industrial strain in China, to determine optimal fermentation parameters under different environmental stresses. The maximum total acid content of A. pasteurianus JST-S was 57.14 ± 1.09 g/L, whereas that of A. pasteurianus CICC 20001 reached 48.24 ± 1.15 g/L in a 15-L stir stank. Metabolic flux analysis was also performed to compare the reaction byproducts. Our findings revealed the potential value of the strain in improvement of industrial vinegar fermentation.

Malic acid production by chemically induced Aspergillus niger MTCC 281 mutant from crude glycerol

In the present investigation, crude glycerol derived from transesterification process was utilized to produce the commercially-valuable malic acid. A combined resistant on methanol and malic acid strain of Aspergillus niger MTCC 281 mutant was generated in solid medium containing methanol (1-5%) and malic acid (40-80 g/L) by the adaptation process for 22 weeks. The ability of induced Aspergillus niger MTCC 281 mutant to utilize crude glycerol and pure glycerol to produce malic acid was studied. The yield of malic acid was increased with 4.45 folds compared with that of parent strain from crude glycerol. The highest concentration of malic acid from crude glycerol by using beneficial mutant was found to be 77.38 ± 0.51 g/L after 192 h at 25 °C. This present study specified that crude glycerol by-product from biodiesel production could be used for producing high amount of malic acid without any pretreatment.