Valorization of egg shell as a detoxifying and buffering agent for efficient polymalic acid production by Aureobasidium pullulans NRRL Y-2311-1 from barley straw hydrolysate

Raw biowaste conversion to high-value compounds for food, cosmetic and pharmaceutical industries

Biowaste valorisation into high-value compounds is one of the main challenges of green chemistry, as chemicals produced from biological sources are identified as key substances in the development of a low-carbon and circular bioeconomy in connection with the transition from fossil to renewable feedstocks. The review summarizes the production of high-value products such as glucose-based chemicals, phenolic compounds and volatile-fatty acids prepared from biomass waste. Biowaste pretreatment methods such as milling, filtration and extraction followed by current non-catalytic methods such as microwave or ultrasound extraction and catalytic methods for the production value-added compounds in the presence of various catalyst types in conventional, nano or enzyme form are listed with a focus on value-added chemicals applied in the food, cosmetic and pharmaceutical industries. The economic feasibility, technical aspects and concept of the biorefinery are briefly mentioned, emphasizing the necessity of life cycle assessment for each bioproduct and technological process. Finally, it provides a future perspective and makes recommendations for potential research strategies, recognizing the importance of utilizing biomass waste for the production of useful compounds as an attractive and environmentally friendly approach whose development should be encouraged. The utilization of biowaste for high-value chemicals production shows high potential, however, there are still many challenges to be resolved throughout the entire production chain, reflecting technological, economic, ecological, sociological and long-term issues.

Advances in Aureobasidium research: Paving the path to industrial utilization

We here explore the potential of the fungal genus Aureobasidium as a prototype for a microbial chassis for industrial biotechnology in the context of a developing circular bioeconomy. The study emphasizes the physiological advantages of Aureobasidium, including its polyextremotolerance, broad substrate spectrum, and diverse product range, making it a promising candidate for cost-effective and sustainable industrial processes. In the second part, recent advances in genetic tool development, as well as approaches for up-scaled fermentation, are described. This review adds to the growing body of scientific literature on this remarkable fungus and reveals its potential for future use in the biotechnological industry.

Unveiling malic acid biorefinery: Comprehensive insights into feedstocks, microbial strains, and metabolic pathways

The over-reliance on fossil fuels and resultant environmental issues necessitate sustainable alternatives. Microbial fermentation of biomass for malic acid production offers a viable, eco-friendly solution, enhancing resource efficiency and minimizing ecological damage. This review covers three core aspects of malic acid biorefining: feedstocks, microbial strains, and metabolic pathways. It emphasizes the significance of utilizing biomass sugars, including the co-fermentation of different sugar types to improve feedstock efficiency. The review discusses microbial strains for malic acid fermentation, addressing challenges related to by-products from biomass breakdown and strategies for overcoming them. It delves into the crucial pathways and enzymes for malic acid production, outlining methods to optimize its metabolism, focusing on enzyme regulation, energy balance, and yield enhancement. These insights contribute to advancing the field of consolidated bioprocessing in malic acid biorefining.

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.

Efficient polymalic acid production from corn straw hydrolysate by detoxification of phenolic inhibitors

Inhibitory compounds generated from lignocellulose pretreatment would inhibit Poly (malic acid) (PMA) production by Aureobasidium pullulans, but the tolerance mechanism of A. pullulans to lignocellulosic inhibitor is poorly understood. In this study, the cellular response of A. pullulans to lignocellulosic inhibitor stress was studied. Among the three groups of inhibitors (furans, weak acids and phenolic aldehydes), phenolic aldehyde was the dominant inhibitor for PMA production. Phenolic aldehyde was mainly converted into phenolic alcohol by A. pullulans, and phenolic alcohol also exhibited severe inhibition on PMA production. Furthermore, the effect of detoxification methods on inhibitor-removal and PMA fermentation was investigated, both CaCO3 and overliming presented poor detoxification effect, whereas resin H103 could remove both furan derivatives and phenolic compounds efficiently, thereby producing 26.27 g/L of PMA with a yield of 0.30 g/g in batch fermentation. This study will be beneficial for the development of PMA production from lignocellulosic biomass.

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

Use of Incinerated Eggshells to Produce Pidan

Preserved eggs (pidans) are used in traditional Chinese cuisines. However, the alkaline conditions and metal ions generated during its preparation have caused some concerns. This study developed an innovative process for pidan processing using incinerated eggshell powder, an abundant by-product that can generate a highly alkaline solution and provide calcium ions (Ca2+). Either 0.5, 3, or 5% of the eggshell powder solution was used for basic pickling. Different combinations of ZnSO4 (0.175%), MgCl2 (0.08%), and CuSO4 (0.16%) were added. Duck eggs were pickled for 25 days at 25–27 °C, followed by 14 days of ripening. The pidan processed in 5% eggshell powder containing 0.175% ZnSO4 demonstrated the closest physiochemical and sensory characteristics to commercial pidans. Thus, the results offer a new technique to manufacture pidans and reduce the harmful impact of metal ions on human health and the environment.

Efficient poly(β-L-malic acid) production from cassava hydrolysate by cell recycle of Aureobasidium pullulans

Poly(β-L-malic acid) (PMLA) is a water-soluble, biodegradable, and biocompatible polymer with broad prospective applications and can be hydrolyzed to produce widely used acidulant L-malic acid. In order to meet an increasing demand of PMLA, we employed two effective cell-recycling strategies to produce PMLA from raw cassava hydrolysate by Aureobasidium pullulans ZD-3d. In fed-batch fermentation with raw cassava hydrolysate, 101.9 g/L PMLA was obtained with the productivity and yield of 0.77 g/L/h and 0.40 g/g, respectively. Further, three times of membrane filtration-based cell recycling fermentation was carried out, with a high productivity and yield of 1.04-1.64 g/L/h and 0.5-0.84 g/g achieved, respectively. While harnessing centrifugation-based cell recycling fermentation for five times, the productivity and yield approached 0.98-1.76 g/L/h and 0.78-0.86 g/g, respectively. To our knowledge, the processes showed the highest average PMLA productivity compared with others using low-cost biomass, which offered efficient and economical alternatives for PMLA production. KEY POINTS: • PMLA production from raw cassava hydrolysate by Aureobasidium pullulans was studied • High PMLA productivity and yield were obtained via two cell recycling strategies • The highest average PMLA productivity from low-cost biomass to date was achieved.

A high molecular weight polymalate is synthesized by the whole genome duplicated strain Aureobasidium melanogenum OUC

Polymalate (PMA) produced by the whole genome duplicated strain Aureobasidium melanogenum OUC had a high molecular weight (Mw) of 3.9 × 10⁵ Da while the Mw of PMA produced by A. melanogenum ATCC62921 was 3.8 × 10⁴ Da. Therefore, the purified PMA produced by A. melanogenum OUC could form hydrogel and film and the precipitated Ca²⁺-PMA looked like noodle whereas the purified PMA produced by A. melanogenum ATCC62921 could not form such a hydrogel and a film and the precipitated PMA was powder-like. The high Mw PMA biosynthesis in A. melanogenum OUC was also controlled by the PMA synthetase. However, it was still unclear why the PMA synthetase in A. melanogenum OUC could catalyze the high Mw PMA biosynthesis. Both removal of two copies of the PKS genes and overexpression of the PYC1 gene, the VGB gene and the CRZ2 gene rendered the new transformant Crz46 to produce 34.6 ± 0.3 g/L of extracellular Ca²⁺-PMA with Mw of 4.9 × 10⁵ Da while its native A. melanogenum OUC only produced 17.2 ± 0.3 g/L of Ca²⁺-PMA. During the 10-Liter fermentation, 35.6 ± 1.2 g/L of Ca²⁺-PMA and 13.9 g/Lof cell mass were produced within 168 h, leading to the yield of 0.36 g/g of glucose and the productivity of 0.21 g/L/h. This was the first time to report that the whole genome duplicated strain A. melanogenum OUC and its engineered mutants could produce the high Mw PMA.

The signaling pathways involved in metabolic regulation and stress responses of the yeast-like fungi Aureobasidium spp

Aureobasidium spp. can use a wide range of substrates and are widely distributed in different environments, suggesting that they can sense and response to various extracellular signals and be adapted to different environments. It is true that their pullulan, lipid and liamocin biosynthesis and cell growth are regulated by the cAMP-PKA signaling pathway; Polymalate (PMA) and pullulan biosynthesis is controlled by the Ca²⁺ and TORC1 signaling pathways; the HOG1 signaling pathway determines high osmotic tolerance and high pullulan and liamocin biosynthesis; the Snf1/Mig1 pathway controls glucose repression on pullulan and liamocin biosynthesis; DHN-melanin biosynthesis and stress resistance are regulated by the CWI signaling pathway and TORC1 signaling pathway. In addition, the HSF1 pathway may control cell growth of some novel strains of A. melanogenum at 37 °C. However, the detailed molecular mechanisms of high temperature growth and thermotolerance of some novel strains of A. melanogenum and glucose derepression in A. melanogenum TN3-1 are still unclear.

Bioconversion of Untreated Corn Hull into L-Malic Acid by Trifunctional Xylanolytic Enzyme from Paenibacillus curdlanolyticus B-6 and Acetobacter tropicalis H-1

L-Malic acid (L-MA) is widely used in food and non-food products. However, few microorganisms have been able to efficiently produce L-MA from xylose derived from lignocellulosic biomass (LB). The objective of this work is to convert LB into L-MA with the concept of a bioeconomy and environmentally friendly process. The unique trifunctional xylanolytic enzyme, PcAxy43A from Paenibacillus curdlanolyticus B-6, effectively hydrolyzed xylan in untreated LB, especially corn hull to xylose, in one step. Furthermore, the newly isolated, Acetobacter tropicalis strain H1 was able to convert high concentrations of xylose derived from corn hull into L-MA as the main product, which can be easily purified. The strain H1 successfully produced a high L-MA titer of 77.09 g/l, with a yield of 0.77 g/g and a productivity of 0.64 g/l/h from the xylose derived from corn hull. The process presented in this research is an efficient, low-cost and environmentally friendly biological process for the green production of L-MA from LB.

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.

Polymalate (PMA) biosynthesis and its molecular regulation in Aureobasidium spp

It has been well documented that different strains of Aureobasidium spp. can synthesize and secrete over 30.0 g/L of polymalate (PMA) and the produced PMA has many potential applications in biomaterial, medical and food industries. The substrates for PMA biosynthesis include glucose, xylose, fructose, sucrose and glucose or fructose or xylose or sucrose-containing natural materials from industrial and agricultural wastes. Malate, the only monomer for PMA biosynthesis mainly comes from TCA cycle, cytosolic reduction TCA pathway and the glyoxylate cycle. The PMA synthetase (a NRPS) containing A like domain, T domain and C like domain is responsible for polymerization of malate into PMA molecules by formation of ester bonds between malates. PMA biosynthesis is regulated by the transcriptional activator Crz1 from Ca²⁺ signaling pathway, the GATA-type transcription factor Gat1 from nitrogen catabolite repression and the GATA-type transcription factor NsdD.

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.

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.