Overview of mechanisms of Fe-based catalysts for the selective catalytic reduction of NOx with NH3 at low temperature.

With the increasingly stringent control of NOx emissions, NH3-SCR, one of the most effective de-NOx technologies for removing NOx, has been widely employed to eliminate NOx from automobile exhaust and industrial production. Researchers have favored iron-based catalysts for their low cost, high activity, and excellent de-NOx performance. This paper takes a new perspective to review the research progress of iron-based catalysts. The influence of the chemical form of single iron-based catalysts on their performance was investigated. In the section on composite iron-based catalysts, detailed reviews were conducted on the effects of synergistic interactions between iron and other elements on catalytic performance. Regarding loaded iron-based catalysts, the catalytic performance of iron-based catalysts on different carriers was systematically examined. In the section on iron-based catalysts with novel structures, the effects of the morphology and crystallinity of nanomaterials on catalytic performance were analyzed. Additionally, the reaction mechanism and poisoning mechanism of iron-based catalysts were elucidated. In conclusion, the paper delved into the prospects and future directions of iron-based catalysts, aiming to provide ideas for the development of iron-based catalysts with better application prospects. The comprehensive review underscores the significance of iron-based catalysts in the realm of de-NOx technologies, shedding light on their diverse forms and applications. The hope is that this paper will serve as a valuable resource, guiding future endeavors in the development of advanced iron-based catalysts.

Enhanced Production of Poly-γ-glutamic Acid by Bacillus subtilis Using Stage-controlled Fermentation and Viscosity Reduction Strategy.

In this study, the production of poly-γ-glutamic acid (PGA) by Bacillus subtilis using stage-controlled fermentation and viscosity reduction strategy was investigated in detail. Based on the single-factor optimization experiment, temperature (42 °C and 37 °C), pH (7.0 and uncontrolled), aeration rate (1.2 vvm and 1.0 vvm), and agitation speed (700 rpm and 500 rpm) were selected for the two-stage controlled fermentation (TSCF). The time points for the TSCF of temperature, pH, aeration rate, and agitation speed were set at 18.52 h, 2.82 h, 5.92 h, and 3.62 h, respectively, based on the kinetic analysis. A PGA titer of 19.79 ~ 22.17 g/L was obtained from the TSCF, which did not increase significantly than that (21.25 ± 1.26 g/L) of non-stage controlled fermentation (NSCF). This may be due to the high viscosity and low dissolved oxygen of the PGA fermentation broth. Thus, the TSCF combined with a viscosity reduction strategy was developed to further improve the production of PGA. The PGA titer reached 25.00 ~ 30.67 g/L, which increased by 17.66 ~ 32.94% to that of NSCF. This study provided a valuable reference for the development of process control strategies for high-viscosity fermentation systems.

Efficient Production of Melanin by Aureobasidium Melanogenum Using a Simplified Medium and pH-Controlled Fermentation Strategy with the Cell Morphology Analysis.

Natural melanin is a biopolymer with wide application prospects in medicine, food, cosmetics, environmental protection, agriculture, and so on. Microbial fermentation is an important and effective way to produce melanin. In this study, Aureobasidium melanogenum, known as black yeast with cellular pleomorphism, was used for the production of melanin. Based on the characteristic of A. melanogenum secreting melanin under oligotrophic stress, a simple medium containing only glucose, MgSO4·7H2O, and KCl was constructed for the production of melanin. The melanin titer of 6.64 ± 0.22 g/L was obtained after 20 days of fermentation without pH control. The cell morphological changes of A. melanogenum during the production of melanin were recorded, and the results showed that chlamydospore might be the most favorable cell morphology for melanin synthesis. Then, different fermentation strategies with cell morphology analysis were developed to further improve the production of melanin in a 5-L fermenter. Results showed that the maximum titer of melanin reached 18.50 g/L by using the fermentation strategy integrating pH control, ammonium salt addition, and H2O2 stimulation, which increased by 178.6% than that of the strategy without pH control. Furthermore, the melanin obtained from the fermentation broth was characterized as eumelanin containing an indole structure. This study provided a potentially feasible fermentation strategy for the industrial production of melanin.

Expression and Purification of Glycosyltransferase DnmS from Streptomyces peucetius ATCC 27952 and Study on Catalytic Characterization of Its Reverse Glycosyltransferase Reaction.

Anthracyclines are an important class of natural antitumor drugs. They have a conservative aromatic tetracycline backbone that is substituted with different deoxyglucoses. The deoxyglucoses are crucial for the biological activity of many bacterial natural products after the proper modification from glycosyltransferases (GTs). The difficulty in obtaining highly purified active GTs has prevented biochemical studies on natural product GTs. In this paper, a new Escherichia coli fusion plasmid pGro7', which introduces the Streptomyces coelicolor chaperone genes groEL1, groES and groEL2, was constructed. The glycosyltransferase DnmS from Streptomyces peucetius ATCC 27952 was co-expressed with the plasmid pGro7', and unprecedented high-efficiency and soluble expression of DnmS in the E. coli expression system was realized. Subsequently, the reverse glycosylation reaction characteristics of DnmS and DnmQ were verified. We found that DnmS and DnmQ had the highest enzyme activity when they participated in the reaction at the same time. These studies provide a strategy for the soluble expression of GTs in Streptomyces and confirm the reversibility of the catalytic reaction of GTs. This provides a powerful method for the production of active anthracyclines and to enhance the diversity of natural products.

Large dynamic strain measurement via slope-assisted Brillouin optical time domain reflectometry using a frequency equalizer.

In this Letter, a method for measuring large dynamic strain via slope-assisted Brillouin optical time domain reflectometry (SA-BOTDR) is proposed. A linear artificial slope created by a frequency equalizer is used instead of the traditional slope of the Brillouin gain spectrum (BGS) as the linear response region between the Brillouin frequency shift (BFS) and signal intensity. This method makes the strain measurement range independent of the bandwidth of the BGS. The large dynamic strain with a maximum value of 3108 µÎµ and the spatial resolution of 5 m along the ∼1.94-km single-mode fiber (SMF) are obtained by means of the proposed technique. Meanwhile, a strong linear relationship is also established between the signal strength and strain at the vibration frequencies of 10.3 and 13.1 Hz. The maximum measured errors of vibration frequency are 0.5 Hz@10.3 Hz and 0.8 Hz@13.1 Hz.

Purification and Characterization of a Fibrinolytic Enzyme from Marine Bacillus velezensis Z01 and Assessment of Its Therapeutic Efficacy In Vivo.

Fibrinolytic enzymes are the most effective agents for the treatment of thrombotic diseases. In the present study, we purified and characterized an extracellular fibrinolytic serine metalloprotease (named Velefibrinase) that is produced by marine Bacillus velezensis Z01 and assessed its thrombolysis in vivo. SDS-PAGE and MALDI-TOF-MS analyses showed that the molecular mass of Velefibrinase was 32.3 KDa and belonged to the peptidase S8 family. The optimal fibrinolytic activity conditions of Velefibrinase were 40 °C and pH 7.0. Moreover, Velefibrinase exhibited high substrate specificity to fibrin, and a higher ratio of fibrinolytic/caseinolytic (1.48) values, which indicated that Velefibrinase had excellent fibrinolytic properties. Based on the degradation pattern of fibrin and fibrinogen, Velefibrinase could be classified as α/ß-fibrinogenase. In vitro, Velefibrinase demonstrated efficient thrombolytic ability, anti-platelet aggregation, and amelioration of blood coagulation (APTT, PT, TT, and FIB), which were superior to those of commercial anticoagulant urokinase. Velefibrinase showed no hemolysis for erythrocyte in vitro and no hemorrhagic activity in vivo. Finally, Velefibrinase effectively prevented mouse tail thrombosis in a dose-dependent (0.22-0.88 mg/kg) manner. These findings suggested that Velefibrinase has the potential to becoming a new thrombolytic agent.

Effects of cell physiological structure on the fermentation broth viscosity during poly-γ-glutamic acid production by Bacillus subtilis GXA-28.

The high viscosity of fermentation broth limited the further improvement of PGA titer. Our previous studies indicated that adding KCl to the medium could decrease the fermentation broth viscosity and improve the PGA titer. In order to clarify the reason, effects of cell physiological structure on the fermentation broth viscosity were investigated. Results from cell morphology observation showed that the reduction of cell aggregation caused by the weakened cross-linking between PGA and cells might be an important reason for the decrease in the fermentation broth viscosity. Besides, when 201.2 mM KCl was added to the medium, the zeta potential of cell surface decreased from - 70.48 ± 3.35 mV to - 81 ± 2.46 mV. The cell membrane integrity was reduced and permeability was enhanced. Furthermore, the percentage of lauric acid C12:0 in cell membrane increased by 12.36%, but palmitic acid C16:0 and stearic acid C18:0 decreased by 6.83% and 5.64%, respectively, which improved the fluidity of cell membrane. The above changes in cell membrane further affect the cross-linking between PGA and cells, thereby playing an important role in reducing the fermentation broth viscosity. This study provided some novel information for understanding the decrease of PGA fermentation broth viscosity by KCl.

An effective combination of codon optimization, gene dosage, and process optimization for high-level production of fibrinolytic enzyme in Komagataella phaffii (Pichia pastoris).

BACKGROUND: As a main drug for diseased thrombus, some clinically used thrombolytic agents have various disadvantages, safer novel thrombolytic agents are of great demand. This study aimed to achieve high and efficient production of a fibrinolytic enzyme with superior enzymatic properties, by a combination strategy of codon optimization, gene dosage and process optimization in Komagataella phaffii (K. phaffii). RESULTS: After codon optimization, the fibase from a marine Bacillus subtilis was expressed and secreted in K. phaffii GS115. Recombinant strains harboring different copies of the fib gene (fib-nc) were successfully obtained via Geneticin (0.25-4 mg/ml) screening on minimal dextrose selection plates and assessment via real-time quantitative PCR. The respective levels of fibase produced by strains expressing fib-5.4c, fib-6c, fib-8c, fib-9c, and fib-12c were 4428, 5781, 7323, 7930, and 2472 U/ml. Levels increased as the copy number increased from 4 to 9, but decreased dramatically at copy number 12. After high cell density fermentation optimization, the highest fibase activity of the strain expressing fib-9c was 7930 U/ml in a shake flask and increased to 12,690 U/ml after 3 days of continuous culture in a 5-L fermenter, which is one of the highest levels of production reported. The recombinant fibase was maximally active at pH 9.0 and 45 °C, and was remarkably stable at pH levels ranging from 5 to 10 and temperatures up to 50 °C. As a metal-dependent serine protease, fibase did not cause hemolysis in vitro and preferentially degraded fibrin directly. CONCLUSIONS: The combination of codon optimization, gene dosage, and process optimization described herein could be used for the expression of other therapeutic proteins difficult to express. The characteristics of the recombinant fibase suggest that it has potential applications for thrombosis prevention and therapy.

Poly(malic acid) production from liquefied corn starch by simultaneous saccharification and fermentation with a novel isolated Aureobasidium pullulans GXL-1 strain and its techno-economic analysis.

In this study, a novel Aureobasidium pullulans GXL-1 strain without melanin secretion was isolated for efficient polymalic acid (PMA) production. The PMA produced by GXL-1 was characterized, and its molecular mass was determined to be 1.621 kDa by gel permeation chromatography. Liquefied corn starch was shown to replace glucose for PMA production by GXL-1 through simultaneous saccharification and fermentation. The PMA titer obtained from batch fermentation was up to 49.0 ± 1.6 g/L in a 10 L fermentor, and the PMA yield and productivity obtained from repeated-batch fermentation were up to 0.50 g/g and 0.34 g/L·h, respectively. Furthermore, process design and techno-economic analysis were performed at an annual output level of 5000 metric tons by SuperPro Designer. Results showed that the production cost of $2.046/kg and payback period of 6.9 years were achieved by repeated-batch fermentation; this provides an economically feasible strategy for industrial-scale production of PMA.

Investigations in ultrasound-assisted anticoagulant production by marine Bacillus subtilis ZHX.

Anticoagulants are the main drugs for the prevention and treatment of thromboembolism. However, most of the present anticoagulants have shortcomings and novel anticoagulants are in great demand. Marine microorganisms are an important source of new drugs. Therefore, in this study, ultrasound was applied to enhance anticoagulant accumulation by marine Bacillus subtilis ZHX. Ultrasound parameters were optimized by single-factor experiments exploring the effects of ultrasound power, duration, duty cycle and the cell growth phases. The optimum conditions were exponential prophase (5 h) with 25 kHz frequency, 140 W power, and a 40% duty cycle for 5 min. The maximum anticoagulant activity (55.36 U/mL) was 1.73 times that of the control group, and the fermentation time was shortened by 3 h. Under optimal conditions, ultrasound increased the carbon utilization by Bacillus subtilis ZHX without significant changes in morphology, favoring cell growth and anticoagulant production. However, excessive ultrasound caused intracellular damage, which inhibited biomass accumulation, decreasing anticoagulant activity and even leading to cell rupture. This is the first report on the use of ultrasound to enhance anticoagulant production by Bacillus, and it provides useful information for scaling-up the process.

Development of a strategy for the screening of α-glucosidase-producing microorganisms.

α-Glucosidase is a crucial enzyme for the production of isomaltooligosaccharide. In this study, a novel method comprising eosin Y (EY) and α-D-methylglucoside (AMG) in glass plates was tested for the primary screening of α-glucosidaseproducing strains. First, α-glucosidase-producing Aspergillus niger strains were selected on plates containing EY and AMG based on transparent zone formation resulting from the solubilization of EY by the hydrolyzed product. Conventional methods that use trypan blue (TB) and p-nitrophenyl-α-D-glucopyranoside (pPNP) as indicators were then compared with the new strategy. The results showed that EY-containing plates provide the advantages of low price and higher specificity for the screening of α-glucosidase-producing strains. We then evaluated the correlation between the hydrolytic activity of α-glucosidase and diffusion distance, and found that good linearity could be established within a 6-75 U/ml enzyme concentration range. Finally, the hydrolytic and transglycosylation activities of α-glucosidase obtained from the target isolates were determined by EY plate assay and 3,5-dinitrosalicylic acid-Saccharomyces cerevisiae assay, respectively. The results showed that the diameter of the transparent zone varied among isolates was positively correlated with α-glucosidase hydrolytic activity, while good linearity could also be established between α-glucosidase transglycosylation activity and non-fermentable reducing sugars content. With this strategy, 7 Aspergillus niger mutants with high yield of α-glucosidase from 200 obvious single colonies on the primary screen plate were obtained.

Purification and biochemical characteristics of a novel fructosyltransferase with a high FOS transfructosylation activity from Aspergillus oryzae S719.

Fructooligosaccharides (FOS) have widely used for the manufacture of low-calorie and functional foods, because they can inhibit intestinal pathogenic microorganism growth and increase the absorption of Ca2+ and Mg2+. In this study, the novel fructosyltransferase (FTase) from Aspergillus oryzae strain S719 was successfully purified and characterized. The specific activity of the final purified material was 4200 mg-1 with purification ratio of 66 times and yield of 26%. The molecular weight of FTase of A. oryzae S719 was around 95 kDa by SDS-PAGE, which was identified as a type of FTase by Mass Spectrometry (MS). The purified FTase had optimum temperature and pH of 55 °C and 6.0, respectively. The FTase showed to be stable with more than 80% of its original activity at room temperature after 12 h and maintaining activity above 90% at pH 4.0-11.0. The Km and kcat values of the FTase were 310 mmol L-1 and 2.0 × 103 min-1, respectively. The FTase was activated by 5 mmol L-1 Mg2+ and 10 mmol L-1 Na+ (relative activity of 116 and 114%, respectively), indicating that the enzyme was Mg2+ and Na+ dependent. About 64% of FOS was obtained by the purified FTase under 500 g L-1 sucrose within 4 h of reaction time, which was the shortest reaction time to be reported regarding the purified enzyme production of FOS. Together, these results indicated that the FTase of A. oryzae S719 is an excellent candidate for the industrial production of FOS.

A Novel Strategy to Regulate 1-Deoxynojirimycin Production Based on Its Biosynthetic Pathway in Streptomyces lavendulae.

This study characterized the biosynthetic pathway of the secondary metabolite 1-deoxynojirimycin (DNJ) from Streptomyces lavendulae. The results revealed that glucose was a preferable precursor for DNJ synthesis, and its carbon skeleton underwent a C2-N-C6 cyclization reaction during synthesis. The biosynthetic pathway was related to the glycolysis pathway, and started from fructose-6-phosphate, and involved amination, dephosphorylation, oxidation, cyclization, dehydration, and reduction reaction steps, yielding DNJ. Then, based on clarified biosynthetic pathway information, precursors, analogs, and metabolism inhibitors were used as novel regulators to enhance the production of DNJ. The results demonstrated that the titer of DNJ could reach 296.56 mg/L, which was 3.3-fold higher than that of a control group (90 mg/L) when sodium citrate (0 h, 5 g/L), sorbose (0 h, 1 g/L), iodoacetic acid (20 h, 50 mg/L), and glucose (26 h, 7 g/L) were added during the fermentation process. This study provides a new understanding of the biosynthetic pathway of DNJ, and also provides an efficient strategy to regulate the production of DNJ based on this biosynthetic pathway, which is a new perspective for the regulation of other secondary metabolites.

Non-sterile Submerged Fermentation of Fibrinolytic Enzyme by Marine Bacillus subtilis Harboring Antibacterial Activity With Starvation Strategy.

Microbial fibrinolytic enzyme is a promising candidate for thrombolytic therapy. Non-sterile production of fibrinolytic enzyme by marine Bacillus subtilis D21-8 under submerged fermentation was realized at a mild temperature of 34°C, using a unique combination of starvation strategy and self-production of antibacterial agents. A medium composed of 18.5 g/L glucose, 6.3 g/L yeast extract, 7.9 g/L tryptone, and 5 g/L NaCl was achieved by conventional and statistical methods. Results showed efficient synthesis of fibrinolytic enzyme and antibacterial compounds required the presence of both yeast extract and tryptone in the medium. At shake-flask level, the non-sterile optimized medium resulted in higher productivity of fibrinolytic enzyme than the sterile one, with an enhanced yield of 3,129 U/mL and a production cost reduced by 24%. This is the first report dealing with non-sterile submerged fermentation of fibrinolytic enzyme, which may facilitate the development of feasible techniques for non-sterile production of raw materials for the preparation of potential drugs with low operation cost.

Cost-effective fibrinolytic enzyme production by Bacillus subtilis WR350 using medium supplemented with corn steep powder and sucrose.

The goal of this study was to develop a cheap and simple medium and to optimize fermentation parameters for fibrinolytic enzyme production by Bacillus subtilis WR350. A low-cost medium containing 35 g/L sucrose, 20 g/L corn steep powder and 2 g/L MgSO4·7H2O was developed via single-factor and orthogonal experiments. A cheap nitrogen source, corn steep powder, was used to replace the soy peptone present in the initial medium. The highest fibrinolytic activity of 5865 U/mL was achieved using the optimized medium in a 100-L fermenter with an aeration rate of 1.0 vvm and an agitation speed of 200 rpm. The resulting enzyme yield was among the highest described in the literature with respect to fibrinolytic activity, as determined by the fibrin plate method. Techno-economic evaluation indicated that the cost of the optimized medium was only 8.5% of the cost of the initial medium, and the total fermentation cost of fibrinolytic enzyme production using the optimized medium was 23.35% of the cost of using the initial medium.

Analysis of the L-malate biosynthesis pathway involved in poly(ß-L-malic acid) production in Aureobasidium melanogenum GXZ-6 by addition of metabolic intermediates and inhibitors.

Poly(ß-L-malic acid) (PMA) is a promising polyester formed from L-malate in microbial cells. Malate biosynthesis is crucial for PMA production. Previous studies have shown that the non-oxidative pathway or oxidative pathway (TCA cycle) is the main biosynthetic pathway of malate in most of PMA-producing strains, while the glyoxylate cycle is only a supplementary pathway. In this study, we investigated the effect of exogenous metabolic intermediates and inhibitors of the malate biosynthetic pathway on PMA production by Aureobasidium melanogenum GXZ-6. The results showed that PMA production was stimulated by maleic acid (a fumarase inhibitor) and sodium malonate (a succinate dehydrogenase inhibitor) but inhibited by succinic acid and fumaric acid. This indicated that the TCA cycle might not be the only biosynthetic pathway of malate. In addition, the PMA titer increased by 18.1% upon the addition of glyoxylic acid after 72 h of fermentation, but the PMA titer decreased by 7.5% when itaconic acid (an isocitrate lyase inhibitor) was added, which indicated that malate for PMA production was synthesized significantly via the glyoxylate cycle rather than the TCA cycle. Furthermore, in vitro enzyme activities of the TCA and glyoxylate cycles suggested that the glyoxylate cycle significantly contributed to the PMA production, which is contradictory to what has been reported previously in other PMA-producing A. pullulans.

Efficient Production of Polymalic Acid by a Novel Isolated Aureobasidium pullulans Using Metabolic Intermediates and Inhibitors.

Polymalic acid (PMA) is a linear anionic polyester composed of L-malic acid monomers, which have potential applications as drug carriers, surgical suture, and biodegradable plastics. In this study, a novel strain of Aureobasidium pullulans var. melanogenum GXZ-6 was isolated and identified according to the morphological observation and deoxyribonucleic acid internal-transcribed spacer sequence analysis, and the product of PMA was characterized by FT-IR, 13C-NMR, and 1H-NMR spectra. The PMA titer of GXZ-6 reached 62.56 ± 1.18 g L-1 with productivity of 0.35 g L-1 h-1 using optimized medium with addition of metabolic intermediates (citrate and malate) and inhibitor (malonate) by batch fermentation in a 10-L fermentor. Besides that the malate for PMA synthesis in GXZ-6 might mainly come from the glyoxylate cycle, based on results, citrate, malate, malonate, and maleate increased while succinate and fumarate inhibited the production of PMA, which was different from that of other A. pullulans. This study provided a potential strain and a simple metabolic control strategy for high-titer production of PMA and shared novel information on the biosynthesis pathway of PMA in A. pullulans.

Spectroscopic techniques investigation on the interaction of glucoamylase with 1-deoxynojirimycin: Mechanistic and conformational study.

1-Deoxynojirimycin (DNJ), a representative polyhydroxylated alkaloids, is widely used in the field of antidiabetic, antitumor, and anti-HIV. The present study tried to clarify the interaction mechanism of DNJ with glucoamylase by multi-spectroscopic techniques, dynamic light scattering in combination with molecular modeling strategies from biophysics point of view. Fluorescence and UV-vis data indicated that fluorescence quenching mechanism of glucoamylase and DNJ was a dynamic manner. The association constant, binding site and thermodynamic parameters were also obtained from fluorescence spectrum at different temperatures. Synchronous fluorescence, circular dichroism and dynamic light scattering methods demonstrated that their interaction induced microenvironment changes around tryptophan residue and protein conformational alteration. The main driving force was hydrophobic interaction and hydrogen bonding. In addition, molecular docking study indicated that 1-deoxynojirimycin could bind in the catalytic domain of glucoamylase and interact with amino acid residues Arg78, Asp79, Glu203 and Glu424 by forming hydrogen bonds. Molecular dynamics simulation demonstrated that profiles of atomic fluctuation remained the rigidity of ligand binding site. This study elucidated the detailed interaction mechanism of DNJ with glucoamylase, which will be helpful for pharmaceutical companies to design new α-glucosidase inhibitor drugs based on polyhydroxylated alkaloids compound like DNJ.

Production of high crystallinity type-I cellulose from Komagataeibacter hansenii JR-02 isolated from Kombucha tea.

In this study, a bacterial cellulose (BC) producing strain was isolated from Kombucha tea and identified as Komagataeibacter hansenii JR-02 by morphological, physiological, and biochemical characterization and 16S rRNA sequence. Then, the media components and culture conditions for BC production were optimized. Result showed that the highest BC yield was 3.14 ± 0.22 and 8.36 ± 0.19 g/L after fermentation for 7 days under shaking and static cultivation, respectively. Moreover, it was interesting that JR-02 could produce BC in nitrogen-free medium with the highest yield of 0.76 ± 0.06 g/L/7days, and the possible nitrogen fixation gene nifH was cloned from its genomic DNA. The BC produced by JR-02 was type-I cellulose with high crystallinity and thermodynamic stability, which was revealed from Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis methods. The crystallinity of static and shaking cultured BC were 91.76% and 90.69%, respectively. The maximum rate of weight loss of static and shaking BC occurred at temperature of approximately 373.1 °C and 369.1 °C, respectively. Overall, these results indicated that K. hansenii JR-02 had great potential to produce high crystallinity type-I BC in manufacture.

Development and benefit evaluation of fermentation strategies for poly(malic acid) production from malt syrup by Aureobasidium melanogenum GXZ-6.

Malt syrup, as a low-cost substrate without any pretreatment, was proved to be able to replace maltose for ploymalic acid (PMA) production by Aureobasidium melanogenum GXZ-6. The PMA titer of 55.53 ±â€¯1.72 g/L was obtained by batch fermentation in a 10-L fermentor with addition of malate, citrate and sodium malonate. Then, a higher PMA titer of 124.07 ±â€¯2.28 g/L was obtained in fed-batch fermentation, which increased by 123.43% than that from batch fermentation. Moreover, repeated-batch fermentation with three batches gave a PMA titer of 64.06 g/L on average with a higher yield of 0.81 g/g and productivity of 0.56 g/L·h. Fermentation process and economics analysis were performed by SuperPro Designer for a 2000 metric tons plant. Results showed that PMA production cost was as low as $ 1.716/kg by fed-batch fermentation, which provides an economical strategy for large-scale PMA production.