Optimization of mineral salts in medium for enhanced production of pullulan by Aureobasidium pullulans HP-2001 using an orthogonal array method

Production and applications of pullulan from lignocellulosic biomass: Challenges and perspectives

Pullulan is an exopolysaccharide produced by Aureobasidium pullulans, with interesting characteristics which lead to its application in industries such as pharmaceuticals, cosmetics, food, and others. To reduce production costs for industrial applications, cheaper raw materials such as lignocellulosic biomass can be utilized as a carbon and nutrient source for the microbial process. In this study, a comprehensive and critical review was conducted, encompassing the pullulan production process and the key influential variables. The main properties of the biopolymer were presented, and different applications were discussed. Subsequently, the utilization of lignocellulosics for pullulan production within the framework of a biorefinery concept was explored, considering the main published works that deal with materials such as sugarcane bagasse, rice husk, corn straw, and corn cob. Next, the main challenges and future prospects in this research area were highlighted, indicating the key strategies to favor the industrial production of pullulan from lignocellulosic biomasses.

Enhanced β-glucan and pullulan production by Aureobasidium pullulans with zinc sulfate supplementation

The effects of mineral salts on the production of exopolysaccharides, including β-glucan and pullulan, by Aureobasidium pullulans CCTCC M 2012259 were investigated. Zinc sulfate at certain concentrations decreased dry biomass but favored to the biosynthesis of both exopolysaccharides. When 100 mg/L zinc sulfate was added to the fermentation medium, production of β-glucan and pullulan increased by 141.7 and 10.2%, respectively, when compared with that noted in the control without zinc sulfate addition. To reveal the physiological mechanism underlying improved β-glucan and pullulan production, key enzymes activities, energy metabolism substances, intracellular uridine diphosphate glucose (UDPG) levels, and gene expression were determined. The results indicated that zinc sulfate up-regulated the transcriptional levels of pgm1, ugp, fks, and kre6 genes, increased activities of key enzymes involved in the biosynthesis of UDPG, β-glucan and pullulan, enhanced intracellular UDPG content, and improved energy supply, all of which contributed to the increment in β-glucan and pullulan production. The present study not only provides a feasible approach to improve the production of exopolysaccharides but also contributes to better understanding of the physiological characteristics of A. pullulans.

Enhanced endoxylanase production by Myceliophthora thermophila with applicability in saccharification of agricultural substrates

The production of enzymes by solid-state fermentation is an interesting process and currently used worldwide as it can be carried out in solid matrix in absence of free water. In present study, Myceliophthora thermophila BJTLRMDU3 produced high titres of endoxylanase (890.55 U/g DR, dry residue) using 5 g rice straw at pH 7.0 and at 45 °C with 1:7 (w/v) solid-to-moisture ratio with inoculum rate of 12 × 10⁶ spores/ml after 4 days in solid-state fermentation. High enzyme titre was produced after moistening the rice straw with solution containing ammonium sulphate (0.4%), K₂HPO₄ (1.0%), MgSO₄·7H₂O (0.3%), FeSO₄·7H₂O (0.03%) and CaCl₂ (0.03%). Addition of sucrose (2% w/v) and ammonium nitrate (2% w/v) further enhanced the endoxylanase production. A high endoxylanase production was achieved at water activity (a _W) of 0.95 (1639.80 U/g DR) that declined drastically below this value. Among different surfactants, Tween 20 (3% v/v) enhanced the secretion of endoxylanase (2047.91 U/g DR). Furthermore, on optimization of K₂HPO₄ concentration, it was found that 0.5% K₂HPO₄ improved (2191.28 U/g DR) endoxylanase production and overall 4.35-folds increase in production of endoxylanase was achieved after optimization of culture conditions. The enzyme has potential to liberate monomeric (xylose) as well as oligomeric (xylotiose, xylotetrose, and xylopantose) sugars from xylan. On saccharification of rice straw and corncob with endoxylanase, maximum yield of reducing sugars was 135.61 and 132.61 mg/g of substrate recorded after 48, and 36 h, respectively.

Understanding response surface optimization of medium composition for pullulan production from de-oiled rice bran by Aureobasidium pullulans

Central composite rotatable design of RSM was used for the optimization of medium composition for pullulan production from de-oiled rice bran by Aureobasidium pullulans in shake-flask fermentations. The sugars from de-oiled rice bran were extracted in distilled water under moist steam pressure and the obtained de-oiled rice bran extract (DRBE) was used for the optimization of medium composition. RSM optimized medium components (DRBE sugars, 3.88%; yeast extract, 0.24%; (NH₄)₂SO₄, 0.06%; K₂HPO₄, 0.57% (w/v), and pH, 5.22) supported 5.48% (w/v) pullulan production and 0.88 (A₆₀₀/100) biomass yield. Coefficient of determination for pullulan production (0.99) and biomass yield (0.99) was close to 1.0 which justifies significance of model. Lack of fit for both responses was non-significant, which shows fitness of quadratic model. FTIR and NMR spectral attributes confirmed the structure of pullulan. XRD patterns verified the amorphous nature of pullulan. De-oiled rice bran was found as a potential substrate for pullulan production.

Utilization of agro waste pectin for the production of industrially important polygalacturonase

In the present study, a variety of agro-industrial wastes have been utilized for meaningful purpose to produce valuable biocatalyst. All wastes used were low cost and easily accessible while, some available throughout the year. A number of bacterial strains isolated from rotten fruits and vegetables were screened for the production of industrially important polygalacturonase (PGase) using pectin present in these agro-industrial wastes. The strain producing maximum PGase was identified as Bacillus licheniformis KIBE-IB3 on the basis of taxonomic studies and 16S rDNA analysis. Among different agro-industrial wastes studied, high yield of PGase was achieved from fermentation broth having wheat bran (1.0%) as a substrate in to the medium supplemented with nitrogen sources in combination of NaNO₃ and yeast extract while KH₂PO₄ was selected as suitable micronutrient. After optimizing fermentation parameters it was noticed that Bacillus licheniformis KIBE-IB3 was capable of producing maximum PGase at 37 °C, pH 7.0 and after 48 h of incubation time. From the current research, wheat bran was proven as a cheap and easily available source throughout the year for hyper production of pectinase. The utilization of the waste will also help to minimize the concerned environmental issues.

Identification and High-level Production of Pulcherrimin in Bacillus licheniformis DW2

Pulcherrimin, a potential biocontrol agent produced by microorganisms, has the promising applications in the agricultural, medical, and food areas, and the low yield of pulcherrimin has hindered its applications. In this study, the red pigment produced by Bacillus licheniformis DW2 was identified as pulcherrimin through the spectrometry analysis and genetic manipulation, and the component of the medium used for pulcherrimin production was optimized. Based on our results, the addition of 1.0 g L^-1 Tween 80 could improve the yield of pulcherrimin, and glucose and (NH₄)₂SO₄ were served as the optimal carbon and nitrogen sources for pulcherrimin synthesis, respectively. Furthermore, an orthogonal array design was applied for optimization of the medium. Under optimized condition, the maximum yield of pulcherrimin was 331.17 mg L^-1, 5.30-fold higher than that of the initial condition, which was the maximum yield reported for pulcherrimin production. Collectively, this study provided a promising strain and a feasible approach to achieve the high-level production of antimicrobial pulcherrimin.

Optimization of culture medium for enhanced production of exopolysaccharide from Aureobasidium pullulans

Polysaccharides produced by microorganisms are utilized for a variety of purposes, including the use in cosmetics and as food additives. More recently, polysaccharides have been exploited by the medical and pharmaceutical industries, and those originated from many species of mushrooms have been especially useful in industrial applications; however, the production and synthesis of these compounds is costly and time consuming. In this study, we developed a method for low-cost production of exopolysaccharide (EPS) that effectively screens components and optimizes medium composition using statistical methods (Plackett-Burman and Box-Behnken design). As a result, we obtained the following optimized medium: sucrose 165.73 g/L, sodium nitrate 3.08 g/L, dipotassium phosphate 1.00 g/L, potassium chloride 0.50 g/L, magnesium sulfate 0.50 g/L, ferrous sulfate 0.01 g/L, and 0.71 g/L of Ashbya gossypii extract. The maximum production of about 29 g/L EPS was achieved in the optimized medium during 84 h batch fermentation.