Structural characterization and solution properties of an acidic branched (1-->3)-beta-D-glucan from Aureobasidium pullulans

Fractionation and characterization of poly(β-L-malic acid) produced by Aureobasidium melanogenum ipe-1

Poly (β-L-malic acid) (PMLA) is attracting industrial interest for its potential application in medicine and other industries, whose functions primarily depend upon its molecular size and chemical structure. Up to now, the fractionation and characterization of PMLA produced by Aureobasidium spp. were still unclear. In this study, the product from A. melanogenum ipe-1 was effectively fractionated using 300 and 50 kDa membranes. During the filtration, the mechanisms of membrane fouling were illegible since the PMLA can both reject and permeate the membrane, while the main fouling mechanism varied between standard blocking and complete blocking during the diafiltration. After fractionation, 14.0, 8.4 and 77.6 % of the PMLAs with M_ws of 75,134, 21,344 and 10,056 Da were distributed in the 300 kDa retentate after diafiltrating, 50 kDa retentate after diafiltrating, and the 50 kDa permeate, respectively. The M_w/M_ns of the PMLAs were 4.12, 1.92, and 1.12 in the three fractions. Based on characteristic spectra of NMR, HPLC and FTIR, the product was not usual L-malic acid monomers, but glucose-terminated PMLA. The glucose was located at the terminal hydroxyl of PMLA. These results would serve as a valuable guide for process design and practical operation in subsequent industrial application.

Comparison of two different in vivo models and an in vitro model for caloric determination of four novel fiber ingredients

The objective of this study was to compare two in vivo methods using pigs and roosters and an in vitro method for determining the caloric value of four fiber sources [i.e., two resistant starches (RS 60 and RS 75), soluble corn fiber (SCF 70), and pullulan]. Metabolizable energy (ME) in pigs and true metabolizable energy (TMEn) in roosters were determined by using 72 barrows and 24 roosters, respectively. A two-step in vitro procedure was used to quantify monosaccharides released. Results of the two in vivo experiments corresponded well with RS 75 having the least caloric value (7.55 MJ/kg in pigs; 6.19 MJ/kg in roosters) and pullulan having the greatest caloric value (12.21 MJ/kg in pigs; 13.94 MJ/kg in roosters). The caloric values for all the fiber ingredients were less (P < 0.05) than in MD both in pigs and in roosters. Despite some limitations, results of the in vitro procedure corresponded well with the in vivo experiments where the concentration of glucose hydrolyzed from RS 60, RS 75, and SCF 70, but not pullulan, was less (P < 0.05) than the concentration of glucose hydrolyzed from MD. However, the greatest accuracy was obtained in the in vivo experiments.

Aureobasidium pullulans culture supernatant significantly stimulates R-848-activated phagocytosis of PMA-induced THP-1 macrophages

Toll-like receptors (TLRs), which recognize a wide range of microbial pathogens and pathogen-related products, play important roles in innate immunology. Macrophages have a variety of TLRs, and pathogen binding to TLR resulted in the activation of macrophages. R-848, an immune response modifier, is an analog of imidazoquinoline derivative and binds to an endosome-localized TLR to exert an anti-viral response on leukocytes. In the present study, we verified that co-treatment of R-848 with other TLR agonists would enhance immune response. The culture supernatant of Aureobasidium pullulans (A. pullulans, which contains predominantly soluble β-glucan), which binds to cell membrane-localized TLR, and to C-type lectin receptor Dectin-1, was treated together with R-848 to THP-1 macrophages. Compared to R-848 treatment alone, co-treatment of R-848 with A. pullulans culture supernatant significantly augmented TNF-α and IL-12p40 cytokine expression. Next, we investigated whether or not apoptotic cell uptake would be increased by co-treatment of R-848 with A. pullulans culture supernatant. To detect engulfed apoptotic cells, we induced apoptosis in human lymphoma Jurkat cells by 5-fluorouracil and stained them with fluorescent dye 5(6)-carboxytetramethylrhodamine (TAMRA), whereas THP-1 macrophage was labeled with fluorescein isothiocyanate-anti-CD14 and determined the percentage increase in TAMRA-positive THP-1 macrophages by flow cytometric assay. Since R-848 or A. pullulans treatment alone stimulated THP-1 macrophages to induce phagocytosis, co-treatment of R-848 with A. pullulans culture supernatant significantly augmented phagocytosis of apoptotic Jurkat cells. These results suggest that the activation of several different innate immune receptor pathways may enhance the immune response of R-848 significantly.

A small scale study on the effects of oral administration of the β-glucan produced by Aureobasidium pullulans on milk quality and cytokine expressions of Holstein cows, and on bacterial flora in the intestines of Japanese black calves

BACKGROUND

The β-(1 → 3),(1 → 6)-D-glucan extracellularly produced by Aureobasidium pullulans exhibits immunomodulatory activity, and is used for health supplements. To examine the effects of oral administration of the β-(1 → 3),(1 → 6)-D-glucan to domestic animals, a small scale study was conducted using Holstein cows and newborn Japanese Black calves.

FINDINGS

Holstein cows of which somatic cell count was less than 3 x 10⁵/ml were orally administered with or without the β-(1 → 3),(1 → 6)-D-glucan-enriched A. pullulans cultured fluid (AP-CF) for 3 months, and the properties of milk and serum cytokine expression were monitored. Somatic cell counts were not significantly changed by oral administration of AP-CF, whereas the concentration of solid non fat in the milk tended to increase in the AP-CF administered cows. The results of cytokine expression analysis in the serum using ELISA indicate that the expressions of tumor necrosis factor-α (TNF-α) and interleukin (IL)-6 in all cows which were orally administered with AP-CF became slightly lower than that of control cows after the two-month treatment. On the other hand, IL-8 expression tended to indicate a moderately higher level in all treated cows after the three-month administration of AP-CF in comparison with that of the control cows. Peripartum Japanese Black beef cows and their newborn calves were orally administered with AP-CF, and bacterial flora in the intestines of the calves were analyzed by T-RFLP (terminal restriction fragment length polymorphism). The results suggest that bacterial flora are tendentiously changed by oral administration of AP-CF.

CONCLUSIONS

Our data indicated the possibility that oral administration of the β-(1 → 3),(1 → 6)-D- glucan produced by A. pullulans affects cytokine expressions in the serum of Holstein cows, and influences bacterial flora in the intestines of Japanese Black calves. The findings may be helpful for further study on the efficacies of oral administration of β-(1 → 3),(1 → 6)-D-glucans on domestic animals.

Current knowledge on biosynthesis, biological activity, and chemical modification of the exopolysaccharide, pullulan

The article presents an overview of the latest advances in investigations of the biosynthesis, molecular properties, and associated biological activity of pullulan. The literature survey on the pullulan biosynthesis is intended to illustrate how the great variety of environmental conditions as well as variability in strain characteristics influences the metabolic pathways of the pullulan formation and effects structural composition of the biopolymer. Molecular properties of pullulan as alpha-(1-->4)- and alpha-(1-->6)-glucan are discussed in terms of similarities with amylose and dextran structures, and an emphasis is made on the inherent biological activity of pullulan molecules. The author also attempts to summarize the concepts, options, and strategies in chemical modification of the biopolymer and to delineate future prospects in designing new biologically active derivatives.

Specificity and direction of depolymerization of beta-poly(L-malate) catalysed by polymalatase from Physarum polycephalum--fluorescence labeling at the carboxy-terminus of beta-poly(L-malate)

Beta-poly(L-malate), a major constituent of nuclei in plasmodia of Physarum polycephalum, is enzymatically degraded to L-malate after secretion into the culture medium. This depolymerization is specifically catalysed by an endogenous polymalatase. The mode of action and the specificity criteria have been investigated by employing various chemical derivatives of beta-poly(L-malate), including substitution at the hydroxy-terminus and carboxy-terminus of the polymer, esterification of the pending alpha-carboxylate, and beta-poly(DL-malate). The results of the investigation were summarized in a specificity model that involved recognition of the hydroxy-terminus and of the alpha-carboxylate as substituents of the asymmetric carbon in the malic acid unit. Depolymerization proceeded from the hydroxy-terminus towards the carboxy-terminus, thereby degrading the polymer to L-malate. When the terminal beta-carboxylate had been amidated with the fluorescent N-(1-naphthyl)ethylenediamine, degradation was normal but was arrested at the level of the terminal beta-carboxy-substituted dimer. It should be possible to employ polymalatase as a tool for the detection of branching and other modifications of beta-poly(L-malate).