[Phosphorus dissolving capability, glucose dehydrogenase gene expression and activity of two phosphate solubilizing bacteria].

Objective: To identify the function of glucose dehydrogenase (GDH) and gene expression level in the process of solubilizing phosphorus. Methods: Phosphate solubilizing bacteria (PSB) were isolated and purified by soluble phosphorus circle method, and identified by Vitek 2 system and 16S rRNA sequence. The phosphate solubilization capacity and GDH activity of PSB were determined. GDH genes were cloned by PCR and the relative expression level of both genes under different conditions were determined by real-time quantitative PCR. Results: Two PSB were identified as Pseudomonas sp. and Enterobacter sp. and the highest phosphorus solubilizing capability was 558 µg/mL for the former and 478 µg/mL for the latter. GDH genes of the two bacteria were cloned and the fragments were 2007 bp and 2066 bp. Different GDH activity and GDH gene expression were cultivated under the condition of different phosphorus sources and pH value. GDH gene expression of strain wj1 was higher than the other under high phosphorus, and the result was opposite under phosphorus stress. However, GDH gene expression of strain wj3 was lower in all phosphorus levels. The expression of GDH gene and the change of the enzyme activity were not obviously related with phosphorus solubilizing capability for strain wj3. Conclusion: There were different characteristics of GDH activity and GDH gene expression in two isolated strains that have different phosphate solubilizing mechanisms.

Effects of water chemistry on microfabric and micromechanical properties evolution of coastal sediment: A centrifugal model study.

Water chemistry alteration induced strength weakening of natural sediment, which leads to the differential settlement of infrastructures in coastal areas, has caused numerous disasters and engineering failures. To thoroughly understand the underlying mechanisms of how water chemistry influences the microfabric and mechanical properties evolution of coastal sediments, herein, the authors adopted centrifuge test, X-ray diffraction (XRD), and atomic force microscope (AFM) to quantitatively study the structure anisotropy index (i.e., orientation index (OI)), micromorphological property (i.e., root mean square height (Sq)), and micromechanics (i.e., microscale apparent modulus) of clay sediments in different water chemistry conditions and gravity gradients. The results show that the change rule of OI is: OIsaline > OIalkaline > OIwater > OIacid, along the vertical sedimentary depth. Randomly distributed clay flocs and loose flocculated soil skeleton (mainly consisted by edge-to-face (EF) and edge-to-edge (EE) contact of the kaolinite platelets) are associated with the acidic water chemical conditions. The action of supergravity and face-to-face (FF) repulsive contact mode lead to high degree of anisotropy of kaolinite sediments in alkaline environment. Clay platelets are compacted closely under the synergetic effect of centrifugal pressure and prevailing van der Waals attraction (reduction of electric double layer repulsion) in saline environment. The change of 1/Sq is highly consistent with the change of OI at different depths in different water chemical environments. Along the sedimentary depth (i.e., transition from the normal gravity (1 g) to supergravity (8000 g)), the microscale apparent modulus of kaolinite sediment was found to be the highest in alkaline environment. As the water chemistry changes from alkaline to acidic, however, the microscale apparent modulus of kaolinite aggregate decreased, and it showed the smallest in the saline environment.

Novel ratiometric electrochemical sensing platform with dual-functional poly-dopamine and NiS@HCS signal amplification for sunset yellow detection in foods.

In this work, a novel ratiometric electrochemical sensor based on dual-functional poly-dopamine (PDA) and nickel sulfide@hollow carbon spheres (NiS@HCS) was successfully developed for sunset yellow (SY) detection. The NiS@HCS nanocomposite possessing a large specific surface area, good catalytic activity and excellent electrical conductivity was employed for signal amplification. PDA films prepared by electropolymerization acted as an internal reference probe and enhanced the sensitivity of the proposed sensor through electrostatic attraction between SY and PDA. Under optimized conditions, the developed PDA/NiS@HCS/GCE sensor allowed SY quantification over wide linear range (0.01-100 µM), with a low limit of detection of 0.003 µM. SY recovery tests were carried out in rice vinegar and cooking wine with satisfactory recoveries (83.50-112.80 %). Meanwhile, the content of SY in two kinds of carbonated drinks was determined using the constructed sensor and a UV-Vis spectrometry method, with no significant difference found in the results.