Zn3Sb4O6F6 and KI-Doped Zn3Sb4O6F6: A Metal Oxyfluoride System for Photocatalytic Activity, Knoevenagel Condensation, and Bacterial Disinfection.

Zn3Sb4O6F6 crystallites were synthesized by a pH-regulated hydrothermal synthetic approach, while doping on Zn3Sb4O6F6 by KI was performed by the "incipient wetness impregnation technique." The effect of KI in Zn3Sb4O6F6 is found with the changes in morphology in the doped compound, i.e., needle-shaped particles with respect to the irregular cuboid and granular shaped in the pure compound. Closer inspection of the powder diffraction pattern of doped compounds also reveals the shifting of Braggs' peaks toward a lower angle and the difference in cell parameters compared to the pure compound. Both metal oxyfluoride comprising lone pair elements and their doped compounds have been successfully applied as photocatalysts for methylene blue dye degradation. Knoevenagel condensation reactions were performed using Zn3Sb4O6F6 as the catalyst and confirmed 99% yield even at 60 °C temperature under solvent-free conditions. Both pure and KI-doped compounds were tested against several standard bacterial strains, i.e., Enterobacter sp., Escherichia coli, Staphylococcus sp., Salmonella sp., Bacillus sp., Proteous sp., Pseudomonas sp., and Klebsiella sp. by the "disk diffusion method" and their antimicrobial activities were confirmed.

Characterization of zinc solubilization potential of arsenic tolerant Burkholderia spp. isolated from rice rhizospheric soil.

In this study, experiments were conducted to isolate, characterize, and evaluate rice rhizosphere bacteria for their arsenic (As) tolerance ability and zinc (Zn) solubilization potential in culture media and soil. Among 20 bacterial isolates recovered, six were found to solubilize inorganic Zn salt(s) efficiently under in vitro culture conditions. 16S rRNA gene sequence-based phylogenetic analysis indicated the affiliation of efficient Zn solubilizing bacteria (ZSB) to Burkholderia vietnamiensis and Burkholderia seminalis. Zinc solubilizing efficiency (ZSE) of the bacteria varied with the concentrations and types of Zn salts used in the experiments. Increasing trend in ZSE of the bacteria was noticed when the percentage of ZnO increased from 0.1 to 0.5 but the same decreased at 1.0%. Increased Zn solubilization was noticed when bacteria were incubated with lower concentration of Zn3(PO4)2 and ZnCO3. In general, Zn solubilization increased with increasing incubation time in lower volume medium, while some isolates failed to solubilize one or more tested Zn salts. However, enriched concentrated cells of the ZSB in glucose amended medium with 0.5% ZnO showed an increasing trend of Zn solubilization with time and were able to solubilize more than 300 mg/L Zn. This increased rate of Zn release by the ZSB was attributed to marked decline in pH that might be due to the enhanced gluconic acid production from glucose. As evident from the decreased ZSE of the bacteria in the presence of As(V) in particular, it seems arsenic imparts a negative effect on Zn solubilization. The ZSB were also able to increase the rate of Zn release in soil. A microcosm-based soil incubation study amending the enriched bacteria and 0.5% ZnO in soil showed an elevated level of both water-soluble and available Zn compared to un-inoculated control. During Zn solubilization in microcosms, viable cells in terms of colony-forming unit (CFU) declined by the same order of magnitude both in the presence and absence of ZnO that might be due to the nutrients limiting condition aroused during the incubation period rather than Zn toxicity. The bacteria in this study also exhibited plant growth promoting traits, such as growth in nitrogen-free medium, production of indole acetic acid (IAA), and solubilization of potassium and phosphate. Our findings suggested that Burkholderia spp. could be the potential candidates for enhancing Zn dissolution in the soil that might reduce the rate of inorganic Zn fertilization in agricultural soil.

Characterization of arsenic oxidation and uranium bioremediation potential of arsenic resistant bacteria isolated from uranium ore.

Arsenic (As) is often found naturally as the co-contaminant in the uranium (U)-contaminated area, obstructing the bioremediation process. Although the U-contaminated environment harbors microorganisms capable of interacting with U which could be exploited in bioremediation. However, they might be unable to perform with their full potential due to As toxicity. Therefore, potential in arsenic resistance and oxidation is greatly desired among the microorganisms for a continued bioremediation process. In this study, arsenic-resistant bacteria were isolated from U ore collected from Bundugurang U mine, characterized and their As oxidation and U removal potentials were determined. 16S rRNA gene sequencing and phylogenetic analysis showed the affiliation of isolated bacteria with Microbacterium, Micrococcus, Shinella, and Bacillus. Except Bacillus sp. EIKU7, Microbacterium sp. EIKU5, Shinella sp. EIKU6, and Micrococcus sp. EIKU8 were found to resist more than 400 mM As(V); however, all the isolates could survive in 8 mM As(III). The isolates were found to readily oxidize As under different culture conditions and are also resistant towards Cd, Cr, Co, Ni, and Zn. All the isolates could remove more than 350 mg U/g dry cells within 48 h which were found to be highly dependent upon the concentration of U, biomass added initially, and on the time of exposure. Ability of the isolates to grow in nitrogen-free medium indicated that they can flourish in the nutrition deprived environment. Therefore, the recovery of isolates with the potent ability to resist and oxidize As from U ore might play an important role in toxic metal bioremediation including U.

Elevated level of arsenic negatively influences nifH gene expression of isolated soil bacteria in culture condition as well as soil system.

Comprehensive studies on the effect of arsenic (As) on free-living diazotrophs that play a crucial role in soil fertility by nitrogen fixation are still scanty. Here, we isolated three free-living bacteria from rice field with potential nitrogen-fixing ability and investigated the impact of As on their nifH gene expression and extracellular polysaccharide (EPS) production in culture condition and soil system. 16S rRNA sequence analysis showed that the isolated bacteria were affiliated to ß-Proteobacteria, γ-Proteobacteria and Firmicutes. As(III) exposure to bacterial isolates followed by RT-qPCR analysis revealed that elevated levels of As reduced the expression of nifH gene in selective bacteria, both in culture medium and soil condition. We also noticed reduced production of EPS under higher concentration of As. All the three bacteria showed high tolerance to As(III), able to oxidize As and exhibited significant plant growth-promoting traits. This investigation indicated that an environment exposed with higher concentration of As might perturbed the activity of free-living diazotrophs in agricultural soil system.