New two-stage pH combined with dissolved oxygen control strategy for cyclic ß-1,2 glucans synthesis.

On the basis of a novel two-stage pH combined with dissolved oxygen (DO) control strategy in fed-batch fermentation, this research addresses the influence of pH on cyclic ß-1,2-glucans (CßGs) biosynthesis and melanin accumulation during the production of CßGs by Rhizobium radiobacter ATCC 13,333. Under these optimal fermentation conditions, the maximum cell concentration and CßGs concentration in a 7-L stirred-tank fermenter were 7.94 g L-1 and 3.12 g L-1, which were the maximum production reported for R. radiobacter. The melanin concentration of the fermentation broth was maintained at a low level, which was beneficial to the subsequent separation and purification of the CßGs. In addition, a neutral extracellular oligosaccharide (COGs-1) purified by the two-stage pH combined with DO control strategy fermentation medium was structurally characterized. Structural analyses indicated that COGs-1 was a family of unbranched cyclic oligosaccharides composed of only ß-1,2-linked D-glucopyranose residues with degree of polymerization between 17 and 23, namely CßGs. This research provides a reliable source of CßGs and structural basis for further studies of biological activity and function. KEY POINTS: • A two-stage pH combined with DO control strategy was proposed for CßGs production and melanin biosynthesis by Rhizobium radiobacter. • The final extracellular CßGs production reached 3.12 g L-1, which was the highest achieved by Rhizobium radiobacter. • The existence of CßGs could be detected by TLC quickly and accurately.

Enhanced solubility of curcumin by complexation with fermented cyclic ß-1,2-glucans.

Curcumin (CUR) is a low-solubility polyphenolic compound with many physiological functions. Cyclic ß-1,2-glucans (cyclosophoraoses [Cys]), which contain rings of different sizes with degrees of polymerization ranging from 17 to 23, were obtained from Rhizobium radiobacter ATCC 1333, a soil microorganism. The complexation ability and solubility enhancement of cyclic ß-1,2-glucans with insoluble curcumin were investigated. Phase-solubility analysis revealed that the stoichiometric ratio of the inclusion complexes was 1:1. The stability constant of Cys was 930 M-1, which was 7.68 times that of α-cyclodextrin (α-CD) and 2.09 times that of ß-cyclodextrin (ß-CD). The characteristics of the curcumin/Cys inclusion complexes were successfully determined by using Fourier transform infrared (FTIR) spectrometry, differential scanning calorimetry (DSC), nuclear magnetic resonance (1H NMR) spectroscopy, and scanning electron microscopy (SEM). Moreover, a 1:1 molecular model of the curcumin/Cys inclusion complexes was established through molecular docking analysis. These findings indicated that cyclic ß-1,2-glucans successfully formed complexes with curcumin, which suggested that they could be used as solubility-increasing agents. To the best of our knowledge, this is the first report in which curcumin has been embedded into cyclic ß-1,2-glucans resulting in an increase in its aqueous solubility.

[Biosorption characteristics of Cu2+ by spent substrate of pleurotus oyster].

To solve the problems of heavy metal pollution and agricultural wastes reclamation, spent substrate of pleurotus oyster was used as adsorbents to remove Cu2+ from aqueous solution. The effects of pH value, adsorption time, temperature and initial Cu2+ concentration on the adsorption behavior were determined by single factor experiments. The mechanisms were preliminarily investigated by SEM-EDX, FTIR and XRD analysis. The results of single factor experiments showed that the adsorption rate and capacity reached 74.46% and 0.7446 mg x g(-1) respectively at an adsorbent concentration of 10 g x L(-1), a pH of 6, an adsorption time of 120 min, an adsorption temperature of 30 degrees C and an initial Cu2+ concentration of 8 mg x L(-1). The experimental data fitted well with Langmuir isotherm models and R2 reached 0.994 9, indicating the adsorption was a monolayer chemisorption. SEM-EDX, FTIR and XRD analysis indicated that the adsorption process mainly depended on the physical and chemical adsorption onto the substrate surface through electrostatic attraction, complexation and coordination reaction. The -OH, -COOH and -NH were the functioning groups for Cu2+ adsorption.

[Isolation and identification of imazethapyr degradable bacteria and its degradation characteristics].

One strain of imazethapyr degradable bacteria was isolated from the mixture of imazethapyr production factory's sludge and the soil that was contaminated with imazethapyr for a long time. The strain could degrade imazethapyr more than 90% within 72 h when it grew in 500 mg/L imazethapyr condition. When pH was 5, the bacteria could degrade all the imazethapyr of 500 mg/L in 72 h, but when pH was 8 and 9, only 50% imazethapyr was degraded which showed acid condition was more compatible than that of alkalescency for this bacteria growing. The higher degradation ratio at 25 degrees C and 30 degrees C was observed and the optimum condition for the bacteria to degrade imazethapyr was pH = 5 and 25 degrees C. Characterizing by physiological and biochemical properties as well as 16S rRNA sequence analysis, the strain is related and shared characteristics of the genus Alcaligenes sp.