Adhesion of Sphingomonas sp. GY2B onto montmorillonite: A combination study by thermodynamics and the extended DLVO theory.

Bacterial adhesion on mineral surface are of fundamental importance in geochemical processes and biogeochemical cycling, such as mineral transformation and clay-mediated biodegradation. In this study, thermodynamics analysis combined with classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory as well as the extended DLVO (XDLVO) theory were employed to investigate the adhesion of the Gram-negative PAH-degrading bacteria Sphingomonas sp. GY2B on montmorillonite (Mt). Scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS) indicated the affinity of GY2B for Mt, and the experimental results could be described well by pseudo-second-order (R2 = 0.997) and Langmuir model (R2 = 0.995). The thermodynamics analysis revealed the physical nature of bacterial adhesion onto Mt, which was confirmed by the XDLVO theory. The related surface properties (Zeta potential, hydrodynamic diameter and hydrophobicity) at different ionic strength were determined and the interaction energy between Mt and GY2B were also calculated using the DLVO and XDLVO theories in KCl or CaCl2 solution. At low ionic strength (≤ 20 mM), GY2B adhesion onto Mt was primarily driven by long-range DLVO forces (e.g. electrostatic repulsion), while short-range (separation distance < 5 nm) Van der Waals and hydrophobic interactions played more important roles in the bacterial adhesion at higher ionic strength (50-100 mM). In addition, Mt had a better adhesion capacity to bacteria in Ca2+ solution than that in K+ solution, owing to less negative charge and lower energy barrier in mineral-bacteria system in Ca2+ solution. Overall, the adhesion of bacteria onto Mt could be evaluated well on the basis of the XDLVO theory along with thermodynamics analysis. This study provides valuable insights into the clay-mediated microbial remediation of hydrophobic organic contaminants in the environment.

Immobilization of Sphingomonas sp. GY2B in polyvinyl alcohol-alginate-kaolin beads for efficient degradation of phenol against unfavorable environmental factors.

In this study, batch experiments were carried out to evaluate the biodegradation of phenol by Sphingomonas sp. GY2B, which were immobilized in polyvinyl alcohol (PVA)-sodium alginate-kaolin beads under different conditions. The optimal degradation performance was achieved by GY2B immobilized in beads containing 1.0% (w/v) of kaolin, 10% (w/v) of PVA, 0.3% (w/v) of sodium alginate, 10% (v/v) of biomass dosage, and exposed to an initial phenol concentration of 100 mg/L. The experimental results indicated that PVA-sodium alginate-kaolin beads can accelerate the degradation rate of phenol by reducing the degradation time and also improve degradation rate. The biodegradation rate of phenol by immobilized cells (16.79 ±â€¯0.81 mg/(L·h)) was significantly higher than that of free cells (11.49 ±â€¯1.29 mg/(L·h)) under the above optimal conditions. GY2B immobilized on beads was more competent than free GY2B in degradation under conditions with high phenol concentrations (up to 300 mg/L) and in strong acidic (pH = 1) and alkaline (pH = 12) environments. Higher phenol concentrations inhibit the biomass and reduce the biodegradation rate, while the lower biodegradation rate at low initial phenol concentrations is attributed to mass transfer limitations. The Haldane inhibitory model was in agreement with the experimental data well, revealing that phenol showed a considerable inhibitory effect on the biodegradation by Sphingomonas sp. GY2B, especially at concentrations higher than 90 mg/L. Intra-particle diffusion model analysis suggests that adsorption of phenol by immobilized beads was controlled by both rapid surface adsorption as well as pore diffusion mechanism. It's worth noting that the presence of 1 mg/L Cr(VI) enhanced the biodegradation of phenol by free cells, while Cr(VI) showed no obvious impact on the removal of phenol by immobilized cells. In addition, immobilized cells were reused 16 times and removed 99.5% phenol, and when stored at 4 °C for 90 days, more than 99% phenol was removed. These results showed that immobilized cells can significantly improve the microbial degradation performance, and protect microorganisms against unfavorable environment. It is implied that PVA -sodium alginate-kaolin beads have great potential to be applied in a practical and economical phenolic wastewater treatment system.

Enhanced degradation of phenol by Sphingomonas sp. GY2B with resistance towards suboptimal environment through adsorption on kaolinite.

The effects of clay minerals on microbial degradation of phenol under unfavorable environmental conditions were investigated. Degradation of phenol by Sphingomonas sp. GY2B adsorbed on kaolinite, montmorillonite, and vermiculite were evaluated in comparison with free bacteria under optimal conditions. Kaolinite was found to be the most effective in accelerating degradation rate (reducing the degradation time) as well as improving degradation efficiency (increasing the percentage of phenol degraded), with GY2B/kaolinite complex achieving a degradation efficiency of 96% within 6 h. GY2B adsorbed on kaolinite was more competent than free GY2B in degradation under conditions with high phenol concentrations and at alkaline pH. Kaolinite reduced the time required for degradation by 8-12 h and improved the degradation efficiency by as much as 82% at high phenol concentrations. Meanwhile, the GY2B/kaolinite complex reduced the degradation time by 24 h and improved the degradation efficiency by 46% at pH 12. The improvement was partially due to the buffering effects of kaolinite. It was also shown that Cr(VI) and kaolinite synergistically enhanced the degradation by GY2B, with Cr(VI) and kaolinite both increasing the degradation rate and kaolinite being primarily responsible for enhanced degradation efficiency. These results showed one of the common clay minerals, kaolinite, is able to significantly improve the microbial degradation performance, and protect microorganisms against unfavorable environment. Kaolinite can collaborate with Cr(VI) to further improve the microbial degradation performance. It is implied that clay minerals have great potential to be applied in enhancing the biodegradation of phenol.

Effects of nano bamboo charcoal on PAHs-degrading strain Sphingomonas sp. GY2B.

Nano bamboo charcoal (NBC) has been commonly used in the production of textiles, plastics, paint, etc. However, little is known regarding their effects towards the microorganisms. The effects of NBC on phenanthrene degrading strain Sphingomonas sp. GY2B were investigated in the present study. Results showed that the addition of NBC could improve the phenanthrene removal by Sphingomonas sp. GY2B, with removal efficiencies increased by 10.29-18.56% in comparison to the control at 24h, and phenanthrene was almost completely removed at 48h. With the presence of low dose of NBC (20 and 50mgL(-1)), strain GY2B displayed a better growth at 6h, suggesting that NBC was beneficial to the growth of GY2B and thus resulting in the quick removal of phenanthrene from water. However, the growth of strain GY2B in high dose of NBC (200mgL(-1)) was inhibited at 6h, and the inhibition could be attenuated and eliminated after 12h. NBC-effected phenanthrene solubility experiment suggested that NBC makes a negligible contribution to the solubilization of phenanthrene in water. Results of electronic microscopy analysis (SEM and TEM) indicated NBC may interact with the cell membrane, causing the enhanced membrane permeability and then NBC adsorbed on the membrane would enter into the cells. The findings of this work would provide important information for the future usage and long-term environmental risk assessment of NBC.

Rapid degradation of phenanthrene by using Sphingomonas sp. GY2B immobilized in calcium alginate gel beads.

The strain Sphingomonas sp. GY2B is a high efficient phenanthrene-degrading strain isolated from crude oil contaminated soils that displays a broad-spectrum degradation ability towards PAHs and related aromatic compounds. This paper reports embedding immobilization of strain GY2B in calcium alginate gel beads and the rapid degradation of phenanthrene by the embedded strains. Results showed that embedded immobilized strains had high degradation percentages both in mineral salts medium (MSM) and 80% artificial seawater (AS) media, and had higher phenanthrene degradation efficiency than the free strains. More than 90% phenanthrene (100 mg x L(-1)) was degraded within 36 h, and the phenanthrene degradation percentages were >99.8% after 72 h for immobilized strains. 80% AS had significant negative effect on the phenanthrene degradation rate (PDR) of strain GY2B during the linear-decreasing stage of incubation and preadsorption of cells onto rice straw could improve the PDR of embedded strain GY2B. The immobilization of strain GY2B possesses a good potential for application in the treatment of industrial wastewater containing phenanthrene and other related aromatic compounds.