Disruption of the pullulan synthetase gene in siderophore-producing Aureobasidium pullulans enhances siderophore production and simplifies siderophore extraction

Genome mining the black-yeast Aureobasidium pullulans NRRL 62031 for biotechnological traits

Aureobasidium pullulans is a yeast-like fungus known for its commercial biomanufacturing of pullulan. This study explores the genome of A. pullulans NRRL 62031, highlighting its biosynthetic potential, metabolic pathways, and physiological traits. Additionally, it demonstrates actual product formation and links molecular features to biotechnological applications. Phylogenetic analysis suggested it might be closely related to Aureobasidium melanogenum. While the functional annotation revealed a wide carbohydrate catabolism, growth evaluation demonstrated that the microbe can utilize not only saccharides but also polyols and organic acids. The extracellular cellulolytic, xylanolytic, and pectinolytic activities were indicated by the formation of visible halos on agar plates. The antiSMASH pipeline, NCBI Blastp alignment, and product qualification confirmed that A. pullulans NRRL 62031 can produce melanin, pullulan, polymalate, and polyol lipids. Moreover, yanuthone D, burnettramic acid A, choline, fructooligosaccharides, gluconic acid, and β-glucan might be synthesized by A. pullulans NRRL 62031. The results clearly show the extraordinary potential of A. pullulans NRRL 62031 as a microbial chassis for valorizing biomass residues into value-added bioproducts. The strong catabolic and anabolic capacities indicate significant promise for biotechnological applications. The results are discussed in the context of metabolic engineering of Aureobasidium.

Overexpression of the pullulan synthetase gene enhanced pullulan production and its molecular weight by a mutant of Aureobasidium melanogenum P16

The pullulan synthetase gene (PUL1), involved in pullulan biosynthesis in Aureobasidium species, remains poorly understood. The open reading frame (ORF) of the PUL1 gene from the high pullulan-producing yeast Aureobasidium melanogenum P16 strain was cloned and characterized. The ORF of the PUL1 gene was determined to be 592 bp in length, encoding 178 amino acid residues. It was observed that an intron of 55 bp disrupted the gene. The promoter of the PUL1 gene contained a CAAT box, a TATA box, and a 5'-HGATAR-3' sequence. The deduced protein possessed a signal peptide comprising 18 amino acids and harbored five potential N-glycosylation sites. Following the disruption of the PUL1 gene in strain P16, the disruptant DP108 yielded 34.7 ± 0.3 g/L of pullulan from sucrose, significantly lower than the production by its wild-type strain P16. This discrepancy underscored the close association between the PUL1 gene and pullulan biosynthesis. The majority of the fused Gfp-Pul1 proteins were found to be localized in the cell membrane and on the surface of vacuoles within the yeast-like fungal cells, indicating that pullulan biosynthesis occurred at these subcellular sites. Following the overexpression of the PUL1 gene, strain G14 produced >72.0 g/L of pullulan from sucrose, surpassing the production of its wild-type counterpart strain P16, which yielded 65.5 g/L of pullulan under the identical conditions. This outcome demonstrated that the overexpression of the PUL1 gene significantly enhanced pullulan production. The apparent molecular mass of the purified pullulan increased to 4.4 × 105 Da. As an auxiliary protein, Pul1 was predicted to bind to AmAgs2, the key enzyme in pullulan biosynthesis, facilitating enhanced pullulan production.

Recent advances in the biosynthesis of fungal glucan structural diversity

Glucans are the most abundant class of macromolecule polymers in fungi, which are commonly found in Ascomycota and Basidiomycota. Fungal glucans are not only essential for cell integrity and function but also crucial for the immense industrial interest in high value applications. They present a variety of structural characteristics at the nanoscale due to the high regulation of genes and the involvement of stochastic processes in synthesis. However, although recent findings have demonstrated the genes of glucans synthesis are relatively conserved across diverse fungi, the formation and organization of diverse glucan structures is still unclear in fungi. Here, we summarize the structural features of fungal glucans and the recent developments in the mechanisms of glucans biosynthesis. Furthermore, we propose the engineering strategies of targeted glucan synthesis and point out the remaining challenges in the synthetic process. Understanding the synthesis process of diverse glucans is necessary for tailoring high value glucan towards specific applications. This engineering strategy contributes to enable the sustainable and efficient production of glucan diversity.

Pullusurfactins A‒C, new biosurfactants produced by Aureobasidium pullulans A11231-1-58 from Chrysanthemum boreale Makino

Biosurfactants have found widespread use across multiple industrial fields, including medicine, food, cosmetics, detergents, pulp, and paper, as well as the degradation of oil and fat. The culture broth of Aureobasidium pullulans A11231-1-58 isolated from flowers of Chrysanthemum boreale Makino exhibited potent surfactant activity. Surfactant activity-guided fractionation led to the isolation of three new biosurfactants, pullusurfactins A‒C (1‒3). Their chemical structures were established through the use of spectroscopic techniques, predominantly 1D and 2D NMR, in conjunction with mass measurements. We evaluated the surface tension activities of isolated compounds. At 1.0 mg l-1, these compounds showed high degrees of surfactant activity (31.15 dyne/cm, 33.75 dyne/cm, and 33.83 dyne/cm, respectively).

Cell wall integrity is required for pullulan biosynthesis and glycogen accumulation in Aureobasidium melanogenum P16

BACKGROUND

Pullulan and glycogen have many applications and physiological functions. However, to date, it has been unknown where and how the pullulan is synthesized in the yeast cells and if cell wall structure of the producer can affect pullulan and glycogen biosynthesis.

METHODS

The genes related to cell wall integrity were cloned, characterized, deleted and complemented. The cell wall integrity, pullulan biosynthesis, glycogen accumulation and gene expression were examined.

RESULTS

In this study, the GT6 and GT7 genes encoding different α1,2 mannosyltransferases in Aureobasidium melanogenum P16 were cloned and characterized. The proteins deduced from both the GT6 and GT7 genes contained the conserved sequences YNMCHFWSNFEI and YSTCHFWSNFEI of a Ktr mannosyltransferase family. The removal of each gene and both the two genes caused the changes in colony and cell morphology and enhanced glycogen accumulation, leading to a reduced pullulan biosynthesis and the declined expression of many genes related to pullulan biosynthesis. The swollen cells of the disruptants were due to increased accumulation of glycogen, suggesting that uridine diphosphate glucose (UDP-glucose) was channeled to glycogen biosynthesis in the disruptants, rather than pullulan biosynthesis. Complementation of the GT6 and GT7 genes in the corresponding disruptants and growth of the disruptants in the presence of 0.6 M KCl made pullulan biosynthesis, glycogen accumulation, colony and cell morphology be restored.

GENERAL SIGNIFICANCE

This is the first report that the two α1,2 mannosyltransferases were required for colony and cell morphology, glycogen accumulation and pullulan biosynthesis in the pullulan producing yeast.

Development of a one-step gene knock-out and knock-in method for metabolic engineering of Aureobasidium pullulans

Aureobasidium pullulans is an increasingly attractive host for bio-production of pullulan, heavy oil, polymalic acid, and a large spectrum of extracellular enzymes. To date, genetic manipulation of A. pullulans mainly relies on time-consuming conventional restriction enzyme digestion and ligation methods. In this study, we present a one-step homologous recombination-based method for rapid genetic manipulation in A. pullulans. Overlaps measuring >40bp length and 10μg DNA segments for homologous recombination provided maximum benefits to transformation of A. pullulans. This optimized method was successfully applied to PKSIII gene (encodes polyketide synthase) knock-out and gltP gene (encodes glycolipid transfer protein) knock-in. After disruption of PKSIII gene, secretion of melanin decreased slightly. The melanin purified from disruptant showed lower reducing capacity compared with that of the parent strain, leading to a decrease in exopolysaccharide production. Knock-in of gltP gene resulted in at least 4.68-fold increase in heavy oil production depending on the carbon source used, indicating that gltP can regulate heavy oil synthesis in A. pullulans.

Bio-products produced by marine yeasts and their potential applications

It has been well documented that the yeasts isolated from different marine environments are so versatile that they can produce various fine chemicals, enzymes, bioactive substances, single cell protein and nanoparticles. Many genes related to the biosynthesis and regulation of these functional biomolecules have been cloned, expressed and characterized. All these functional biomolecules have a variety of applications in industries of food, chemical, agricultural, biofuel, cosmetics and pharmacy. In this review, a summary will be given about these functional biomolecules and their producers of the marine yeasts as well as some related genes in order to draw an outline about necessity for further exploitation of marine yeasts and their bio-products for industrial applications.

A novel biosurfactant produced by Aureobasidium pullulans L3-GPY from a tiger lily wild flower, Lilium lancifolium Thunb

Yeast biosurfactants are important biotechnological products in the food industry, and they have medical and cosmeceutical applications owing to their specific modes of action, low toxicity, and applicability. Thus, we have isolated and examined biosurfactant-producing yeast for various industrial and medical applications. A rapid and simple method was developed to screen biosurfactant-producing yeasts for high production of eco-friendly biosurfactants. Using this method, several potential niches of biosurfactant-producing yeasts, such as wild flowers, were investigated. We successfully selected a yeast strain, L3-GPY, with potent surfactant activity from a tiger lily, Lilium lancifolium Thunb. Here, we report the first identification of strain L3-GPY as the black yeast Aureobasidium pullulans. In addition, we isolated a new low-surface-tension chemical, designated glycerol-liamocin, from the culture supernatant of strain L3-GPY through consecutive chromatography steps, involving an ODS column, solvent partition, silica gel, Sephadex LH-20, and an ODS Sep-Pak cartridge column. The chemical structure of glycerol-liamocin, determined by mass spectrometry and nuclear magnetic resonance spectroscopy, indicates that it is a novel compound with the molecular formula C33H62O12. Furthermore, glycerol-liamocin exhibited potent biosurfactant activity (31 mN/m). These results suggest that glycerol-liamocin is a potential novel biosurfactantfor use in various industrial applications.