Effects of nitrogen availability on polymalic acid biosynthesis in the yeast-like fungus Aureobasidium pullulans

Role of AplaeA in the regulation of spore production and poly(malic acid) synthesis in Aureobasidium pullulans

Poly(malic acid) (PMLA) as one of the important metabolites in Aureobasidium pullulans has great application in a variety of fields. LaeA, a global regulator capable of controlling fungal secondary metabolites, has been identified in A. pullulans. The involvement of LaeA in the biosynthesis of PMLA through direct or indirect means and its role in A. pullulans is currently unknown. Here we extracted and characterized the AplaeA gene from A. pullulans HIT-LCY3T and resolved it by bioinformatics. The function of AplaeA was subsequently characterized by Rnai-LaeA and OEX-LaeA mutants. Based on phenotypic observations of the mutant strains, it was found that the gene had a large effect on the morphology and melanin production aspects of the strain, and that overexpression of the AplaeA gene resulted in a substantial increase in spore numbers. RT-qPCR combined with protein interactions results analyzed that ApLaeA positively regulates PMLA biosynthesis by controlling the expression of core genes of PMLA biosynthesis gene cluster and other related regulatory factors. Finally, OEX-LaeA was used as the starting strain to obtain the optimal fermentation conditions. These findings illustrate the regulatory mechanism of a hypothesized global regulator, LaeA, in A. pullulans HIT-LCY3T, suggesting its potential application in industrial-scale PMLA biosynthesis.

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.

Biosynthesis of poly(β-L-malic acid) from rubberwood enzymatic hydrolysates in co-fermentation by Aureobasidium pullulans

Co-fermentation of multiple substrates has emerged as the most effective method to improve the yield of bioproducts. Herein, sustainable rubberwood enzymatic hydrolysates (RWH) were co-fermented by Aureobasidium pullulans to produce poly(β-L-malic acid) (PMA), and RWH + glucose/xylose was also investigated as co-substrates. Owing to low inhibitor concentration and abundant natural nitrogen source content of RWH, a high PMA yield of 0.45 g/g and a productivity of 0.32 g/L/h were obtained by RWH substrate fermentation. After optimization, PMA yields following the fermentation of RWH + glucose and RWH + xylose reached 59.92 g/L and 53.71 g/L, respectively, which were 52 % and 36 % higher than that after the fermentation of RWH. RWH + glucose more significantly affected the correlation between PMA yield and substrate concentration than RWH + xylose. The results demonstrated that the co-fermentation of RWH co-substrate is a promising method for the synthesis of bioproducts.

Engineering the reductive tricarboxylic acid pathway in Aureobasidium pullulans for enhanced biosynthesis of poly-L-malic acid

Aureobasidium pullulans produced poly-L-malic acid (PMA) as the main metabolite in fermentation but with relatively low productivity and yield limiting its industrial application. In this study, A. pullulans ZX-10 was engineered to overexpress cytosolic malate dehydrogenase (MDH) and pyruvate carboxylase (PYC) and PMA synthetase (PMS) using a high-copy yeast episomal plasmid with the gpdA promoter from Aspergillus nidulans. Overexpressing endogenous PMS and heterologous MDH and PYC from Aspergillus oryzae respectively increased PMA production by 19 % - 37 % (0.64 - 0.74 g/g vs. 0.54 g/g for wild type) in shake-flask fermentations, demonstrating the importance of the reductive tricarboxylic acid (rTCA) pathway in PMA biosynthesis. A. pullulans co-expressing MDH and PYC produced 96.7 g/L PMA at 0.90 g/L∙h and 0.68 g/g glucose in fed-batch fermentation, which were among the highest yield and productivity reported. The engineered A. pullulans with enhanced rTCA pathway is advantageous and promising for PMA production.

Using Machine Learning Methods to Predict the ß-Poly (L-Malic Acid) Production by Different Substrates Addition and Secondary Indexes in Strain Aureobasidium melanogenum

ß-poly (L-malic acid) (PMLA) is a polyester ligated by malate subunits. It has a wide prospective application as an anti-cancer drug carrier, and its malate subunits have a great application in the food industry. The strain Aureoabsidium melanogenum could produce a high amount of PMLA during fermentation, and different substrates addition could influence the production. In this study, we directly added potassium acetate, corn steep liquor, MgSO4, MnSO4, vitamin B1, vitamin B2, and nicotinamide as the fermentation substrate to the basic fermentation medium based on a generated random matrix that represented the added value. The PMLA production and four secondary indexes, pH, biomass, osmotic pressure, and viscosity were measured after 144 h fermentation. Finally, a total of 212 samples were collected as the dataset, by which the machine learning methods were deployed to predict the PMLA production by different substrates’ concentrations and the secondary indexes. The results indicated that PMLA production was negatively correlated with corn steep liquor and betaine and positively correlated with potassium acetate. The PMLA production could be predicted using all different substrates’ concentrations with a Mean Absolute Error (MAE) of 4.164 g/L and with an MAE of 6.556 g/L by different secondary indexes. Finally, the convolutional neural network (CNN) was applied to predict the PMLA production by fermentation medium images, in which the collected images were categorized into three groups, 0–20 g/L, 21–40 g/L, and >41 g/L, based on the PMLA production. The CNN model could predict the production with high accuracy. The methods and results presented in this study provided new insight into evaluating different substrates concentration on PMLA production and demonstrating the possibility of using the convolutional neural network model in the PMLA fermentation industry.

Extracellular polysaccharides purified (Polycan) from Aureobasidium pullulans SM‑2001 improves pathophysiology of dystrophin-deficient mdx mice

Background

Duchenne muscular dystrophy is a hereditary muscular disease involving degeneration (i.e. atrophy and loss of muscle fibres) of skeletal muscles, including the diaphragm, and progressively severe functional decline. A previous study shows Polycan, a type of β-glucan derived from the black yeast Aureobasidium pullulans (SM-2001), promotes osteogenicity and bone loss, and possesses anti-inflammatory activity to induce inflammatory cytokines in human immune and cancer cells.

Objective

In this study, we evaluated changes in exercise load behaviour measurements and changes in muscle-related physiological indicators following oral administration of Polycan in mdx mice, an experimental animal model of Duchenne muscular dystrophy.

Result

In mdx mice, Polycan prevented weight loss and thickness of skeletal muscle. In addition, by monitoring increases in running time of mice on treadmills and performing a grip strength test, we confirmed reduced muscle function was recovered to some extent after administering Polycan to mdx mice. In addition, we confirmed that Polycan significantly altered mRNA expression in a concentration-dependent manner, whereby myogenic transcription factors (MyoD, Myf5 and Myogenin) increased and FoxO3α, MuRF1 and Atrogin-1 decreased. We aimed to investigate the mechanism of action in Polycan on energy metabolism of p-AMPK, SIRT1 and PGC1α with apoptosis expression levels as factors related to signalling pathways. Expression ratios of cleaved-caspase-3/caspase-3 and Bax/Bcl-2 in the Polycan extract-administered group increased compared with the control group.

Conclusion

These results demonstrate that Polycan can improve and protect muscle atrophy by preventing apoptosis via pathway regulation related to myogenic transcription factors and energy metabolism in mdx mice.

Polymalic acid for translational nanomedicine

With rich carboxyl groups in the side chain, biodegradable polymalic acid (PMLA) is an ideal delivery platform for multifunctional purposes, including imaging diagnosis and targeting therapy. This polymeric material can be obtained via chemical synthesis, or biological production where L-malic acids are polymerized in the presence of PMLA synthetase inside a variety of microorganisms. Fermentative methods have been employed to produce PMLAs from biological sources, and analytical assessments have been established to characterize this natural biopolymer. Further functionalized, PMLA serves as a versatile carrier of pharmaceutically active molecules at nano scale. In this review, we first delineate biosynthesis of PMLA in different microorganisms and compare with its chemical synthesis. We then introduce the biodegradation mechanism PMLA, its upscaled bioproduction together with characterization. After discussing advantages and disadvantages of PMLA as a suitable delivery carrier, and strategies used to functionalize PMLA for disease diagnosis and therapy, we finally summarize the current challenges in the biomedical applications of PMLA and envisage the future role of PMLA in clinical nanomedicine.

The biosynthesis of polymalic acid (PMLA) and its biotechnical high-grade production from microorganisms compared with the chemical synthesis of PMLA

The physicochemical and biological characteristics of PMLA and its derivatives

How PMLA’s general chemical characteristics can be used to generate various macromolecular compounds for pharmaceutical delivery

The concepts of biological and clinical targeting exemplified by PMLA-based drugs and imaging agents and their biodistribution and biodegradability

An evaluation of the mechanisms that generate preclinical antitumor efficacy and the translational potential for clinical imaging

Techno economic analysis of malic acid production using crude glycerol derived from waste cooking oil

In the present work, Aspergillus niger was employed to produce commercially valuable malic acid from crude glycerol derived from waste cooking oil. Crude glycerol dosage, yeast extract dosage and initial pH were the influencing factors playing a significant role in the malic acid synthesis. The optimal condition for malic acid biosynthesis was studied by using response surface methodology. Further the feasibility analysis for biosynthesis of malic acid from crude glycerol was studied using the laboratory scale optimized data, with this experimentally optimized data, plant was simulated using SuperPro Designer (v10). The cost involved for malic acid synthesis per unit volume was likely expected to be $0.43/kg of malic acid using reactive extraction method. Thus, process optimization combined with techno-economical analysis of malic acid production could be beneficial.

The GATA type transcriptional factors regulate pullulan biosynthesis in Aureobasidium melanogenum P16

Aureobasidium melanogenum P16, the high pullulan producer, had only one GATA type transcriptional activator AreA and one GATA type transcriptional repressor AreB. It was found that 2.4 g/L of (NH₄)₂SO₄ had obvious nitrogen repression on pullulan biosynthesis by A. melanogenum P16. Removal of the AreB gene could make the disruptant DA6 produce 34.8 g/L pullulan while the P16 strain only produced 28.8 g/L pullulan at the efficient nitrogen condition. Further both removal of the native AreA gene and overexpression of the mutated AreA_S628-S678 gene with non-phosphorylatable residues could render the transformant DEA12 to produce 39.8 g/L pullulan. The transcriptional levels of most of the genes related to pullulan biosynthesis in the transformant DEA12 were greatly enhanced. The mutated AreA_S628-S678 was localized in the nuclei of the transformant DEA12 while the native AreA was distributed in the cytoplasm in A. melanogenum P16. This meant that nitrogen repression on pullulan biosynthesis in the transformant DEA12 was indeed significantly relieved. This was the first time to report that the GATA type transcriptional factors of nitrogen catabolite repression system could regulate pullulan biosynthesis in Aureobasidium spp.

Recovery of valuable metals from waste printed circuit boards using organic acids synthesised by Aspergillus niveus

Organic acids such as citric acid, itaconic acid and oxalic acid synthesised by Aspergillus niveus were used for the bioleaching of metals from waste printed circuit boards. Bioleaching of valuable metals was performed in one‐step, two‐steps and spent medium approaches using A. niveus. In the absence of waste printed circuit boards (WPCBs), the dry cell weight of A. niveus was higher when compared with the presence of WPCBs. Variations in the dry cell weight were observed for the presence of different particle sizes. The increase in itaconic acid and oxalic acid synthesis was found at a reduced particle size (60–80 mesh) and reached the maximum titre of itaconic acid (22.35 ± 0.87 mM) and oxalic acid (12.75 ± 0.54 mM) in 12 days during the two‐step bioleaching. The maximum recovery of 75.66% Zn, 73.58% Ni and 80.25% Cu from WPCBs was achieved in 15 days in two‐step leaching with particle sizes of the mesh being 60–80.

Coproduction of polymalic acid and liamocins from two waste by-products from the xylitol and gluconate industries by Aureobasidium pullulans

The coproduction of polymalic acid (PMA) and liamocins, two important metabolites secreted by Aureobasidium pullulans, from two waste by-products from the xylitol and gluconate industries was investigated in shake flasks and fermentors, confirming that waste xylose mother liquor (WXML) could be utilized as an economical feedstock without any pretreatment. Gluconate could strengthen carbon flux and NADPH supply for the synergetic biosynthesis of PMA and liamocins. High PMA and liamocin titers of 82.9 ± 2.1 and 28.3 ± 2.7 g/L, respectively, were obtained from the coupled WXML and waste gluconate mother liquor (WGML) in batch fermentation, with yields of 0.84 and 0.25 g/g, respectively. These results are comparable to those obtained from renewable feedstocks. Economic assessment of the process revealed that PMA and liamocins could be coproduced from two by-products at costs of $1.48/kg or $0.67/kg (with liamocins credit), offering an economic and sustainable process for the application of waste by-products.

Sustainable production and biomedical application of polymalic acid from renewable biomass and food processing wastes

Polymalic acid (PMA), a homopolymer of L-malic acid (MA) generated from a yeast-like fungus Aureobasidium pullulans, has unique properties and many applications in food, biomedical, and environmental fields. Acid hydrolysis of PMA, releasing the monomer MA, has become a novel process for the production of bio-based MA, which currently is produced by chemical synthesis using petroleum-derived feedstocks. Recently, current researches attempted to develop economically competitive process for PMA and MA production from renewable biomass feedstocks. Compared to lignocellulosic biomass, PMA and MA production from low-value food processing wastes or by-products, generated from corn, sugarcane, or soybean refinery industries, showed more economical and sustainable for developing a MA derivatives platform from biomass biorefinery to chemical conversion. In the review, we compared the process feasibility for PMA fermentation with lignocellulosic biomass and food process wastes. Some useful strategies for metabolic engineering are summarized. Its changeable applicability and future prospects in food and biomedical fields are also discussed.

Biosynthetic Polymalic Acid as a Delivery Nanoplatform for Translational Cancer Medicine

Poly(β-L-malic acid) (PMLA) is a natural polyester produced by numerous microorganisms. Regarding its biosynthetic machinery, a nonribosomal peptide synthetase (NRPS) is proposed to direct polymerization of L-malic acid in vivo. Chemically versatile and biologically compatible, PMLA can be used as an ideal carrier for several molecules, including nucleotides, proteins, chemotherapeutic drugs, and imaging agents, and can deliver multimodal theranostics through biological barriers such as the blood–brain barrier. We focus on PMLA biosynthesis in microorganisms, summarize the physicochemical and physiochemical characteristics of PMLA as a naturally derived polymeric delivery platform at nanoscale, and highlight the attachment of functional groups to enhance cancer detection and treatment.

Enhanced malic acid production using Aspergillus niger coupled with in situ product recovery

In the present investigation, recovery of malic acid from the fermentation broth was performed by using in situ reactive extraction method employing different combination of amine and solvent systems. Totally six solvent mixtures were tested for toxicity on Aspergillus niger PJR1. Further, effect of solvent mixture concentration on separation of malic acid was investigated. Solvent system consisting of 2 M of trioctylamine in 1-octanol was found to be non-toxic to A. niger PJR1 and resulted in the maximum partition coefficient of 0.75 when the solvent mixture to liquid ratio of 1:2 used. A. niger PJR1 from crude glycerol using in situ reactive batch fermentation resulted in the maximum malic acid titer of 115.67 ± 3.5 g/L with the productivity of 0.53 g/L.h after 216 h. Further, fed batch extractive fermentation with crude glycerol resulted in malic acid titer of 131.48 ± 3.4 g/L with the productivity of 0.45 g/L.h after 288 h. Thus reactive extraction combined with in situ fermentation could become effective method for enhanced malic acid production.

Production of ethanol and xylanolytic enzymes by yeasts inhabiting rotting wood isolated in sugarcane bagasse hydrolysate

Yeasts associated with rotting wood from four Atlantic Rain forest sites in Brazil were investigated using a culture medium based on sugarcane bagasse hydrolysate. A total of 330 yeast strains were isolated. Pichia manshurica, Candida pseudolambica, and Wickerhamomyces sp. 3 were the most frequently isolated species. Fourteen novel species were obtained in this study. All isolates were tested for their ability to ferment d-xylose and to produce xylanases. In the fermentation assays using d-xylose (30 g L^-1), the main ethanol producers were Scheffersomyces stipitis (14.08 g L^-1), Scheffersomyces sp. (7.94 g L^-1) and Spathaspora boniae (7.16 g L^-1). Sc. stipitis showed the highest ethanol yield (0.42 g g^-1) and the highest productivity (0.39 g L^-1h^-1). The fermentation results using hemicellulosic hydrolysate showed that Sc. stipitis was the best ethanol producer, achieving a yield of 0.32 g g^-1, while Sp. boniae and Scheffersomyces sp. were excellent xylitol producers. The best xylanase-producing yeasts at 50 °C belonged to the species Su. xylanicola (0.487 U mg^-1) and Saitozyma podzolica (0.384 U mg^-1). The results showed that rotting wood collected from the Atlantic Rainforest is a valuable source of yeasts able to grow in sugarcane bagasse hydrolysate, including species with promising biotechnological properties.

Process optimization and kinetic analysis of malic acid production from crude glycerol using Aspergillus niger

In the present work, optimization of crude glycerol fermentation to produce malic acid by using Aspergillus niger was investigated using response surface methodology and artificial neural network. Kinetic investigation of bioconversion of crude glycerol into malic acid using Aspergillus niger was studied using Monod, Mosser, and Haldane-Andrew models. Crude glycerol concentration, initial pH and yeast extract concentration were found to be significant compounds affecting malic acid production by Aspergillus niger. Both dry cell weight and malic acid titre were found decreased with increase in crude glycerol concentration. Haldane-Andrew model gave the best fit for the production of malic acid from crude glycerol with µ_max of 0.1542 h^-1. The maximum malic acid production obtained under optimum conditions was 92.64 + 1.54 g/L after 192 h from crude glycerol using Aspergillus niger.

Malic acid production from biodiesel derived crude glycerol using morphologically controlled Aspergillus niger in batch fermentation

In the present investigation, the effects of crude glycerol concentration, spore inoculum concentration, yeast extract concentration and shaking frequency on seed morphology of Aspergillus niger PJR1 on malic acid production were investigated and dispersed fungal mycelium with higher biomass (20.25 ± 0.91 g/L) was obtained when A. niger PJR1 grow on crude glycerol. Dry cell weight under dispersed fermentation was 21.28% higher than usual pellet fermentation. The optimal crude glycerol, nitrogen source and nitrogen source concentration were found to be 160 g/L, yeast extract and 1.5 g/L, respectively. Batch fermentation in a shake flask culture containing 160 g/L crude glycerol resulted in the yield of malic acid 83.23 ± 1.86 g/L, after 192 h at 25 °C. Results revealed that morphological control of A. niger is an efficient method for increased malic acid production when crude glycerol derived from biodiesel production is used as feedstock.

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.

Enhanced polymalic acid production from the glyoxylate shunt pathway under exogenous alcohol stress

Polymalic acid (PMA) is a water-soluble biopolymer produced by the yeast-like fungus Aureobasidium pullulans. In this study, the physiological response of A. pullulans against exogenous alcohols stress was investigated. Interestingly, ethanol stress was an effective inducer of enhanced PMA yield, although cell growth was slightly inhibited. The stress-responsive gene malate synthase (mls), which is involved in the glyoxylate shunt, was identified and was found to be regulated by exogenous ethanol stress. Therefore, an engineered strain, YJ-MLS, was constructed by overexpressing the endogenous mls gene, which increased the PMA titer by 16.2% compared with the wild-type strain. Following addition of 1% (v/v) of ethanol, a high PMA titer of 40.0 ± 0.38 g/L was obtained using batch fermentation with the mutant YJ-MLS in a 5-L fermentor, with a strongest PMA productivity of 0.56 g/L h. This study was the interesting report to show strengthening of the carbon metabolic flow from the glyoxylate shunt for PMA synthesis, and also provided a new sight for re-recognizing the regulatory behavior of alcohol stress in eukaryotic microbes.

Polymalic acid fermentation by Aureobasidium pullulans for malic acid production from soybean hull and soy molasses: Fermentation kinetics and economic analysis

Polymalic acid (PMA) production by Aureobasidium pullulans ZX-10 from soybean hull hydrolysate supplemented with corn steep liquor (CSL) gave a malic acid yield of ∼0.4g/g at a productivity of ∼0.5g/L·h. ZX-10 can also ferment soy molasses, converting all carbohydrates including the raffinose family oligosaccharides to PMA, giving a high titer (71.9g/L) and yield (0.69g/g) at a productivity of 0.29g/L·h in fed-batch fermentation under nitrogen limitation. A higher productivity of 0.64g/L·h was obtained in repeated batch fermentation with cell recycle and CSL supplementation. Cost analysis for a 5000 MT plant shows that malic acid can be produced at $1.10/kg from soy molasses, $1.37/kg from corn, and $1.74/kg from soybean hull. At the market price of $1.75/kg, malic acid production from soy molasses via PMA fermentation offers an economically competitive process for industrial production of bio-based malic acid.

Production of poly(malic acid) from sugarcane juice in fermentation by Aureobasidium pullulans: Kinetics and process economics

Poly(β-l-malic acid) (PMA) is a biodegradable polymer with many potential biomedical applications. PMA can be readily hydrolyzed to malic acid (MA), which is widely used as an acidulant in foods and pharmaceuticals. PMA production from sucrose and sugarcane juice by Aureobasidium pullulans ZX-10 was studied in shake-flasks and bioreactors, confirming that sugarcane juice can be used as an economical substrate without any pretreatment or nutrients supplementation. A high PMA titer of 116.3g/L and yield of 0.41g/g were achieved in fed-batch fermentation. A high productivity of 0.66g/L·h was achieved in repeated-batch fermentation with cell recycle. These results compared favorably with those obtained from glucose and other biomass feedstocks. A process economic analysis showed that PMA could be produced from sugarcane juice at a cost of $1.33/kg, offering a cost-competitive bio-based PMA for industrial applications.