[Community Distribution of the Rhizospheric and Endophytic Bacteria of Phragmites australis and Their Limiting Factors in Iron Tailings].

The composition of the rhizospheric and endophytic bacteria Phragmites australis in spring and summer around the Qiananling iron tailings reservoir in the Huairou District of Beijing was studied using Illumina high-throughput sequencing technology. Sequencing identified 40 phyla, and Proteobateria and Actinobacteria were the dominant phyla in all samples, accounting for more than 80% of the sequences in all samples. At the genus level, Pseudoarthrobacter was dominant. α-diversity analysis showed that species richness(Sobs, Chao) and species diversity indexes(Shannon, PD) of the rhizosphere soil microorganisms were significantly higher than those of endophytes. The maximum and minimum differences of the Sobs, Chao, Shannon, PD indexes were 1336, 1582.24, 6.48, and 81.18, respectively. ß-diversity analysis indicated that there were significant differences in the community compositions of rhizosphere soil microorganisms and root endophytes, while now notable differences were observed between samples in different seasons. In addition, the dominant strains in each sample(such as Pseudomonas, Arthrobacter, and Streptomyces) were highly resistant to heavy metals. Among the 774 genera, a total of 250 genera coexisted in four types of samples, indicating that the microbial community composition of different samples had some degree of similarity. Correlation analysis between soil physical and chemical properties showed that Ni, Fe, available phosphorus, effective sulphur, and organic matter were significantly related to the microbial communities. Through the prediction of COG function, it was found that the microbial metabolic functions(i.e., energy production and conversion, amino acid transport and metabolism, carbohydrate transport and metabolism, inorganic ion transport, and metabolism) were abundant.

Hematite enhances the removal of Cr(VI) by Bacillus subtilis BSn5 from aquatic environment.

In the present study, we investigated the removal of Cr(VI) and the associated bacterial activity in the systems containing Bacillus subtilis BSn5 (B. subtilis BSn5) and hematite. The microcalorimetry was used to study the effect of hematite on the normal physiological functions of B. subtilis BSn5 towards the removal of Cr(VI) for the first time. The results of the heat flux and the sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that hematite does not affect the normal physiological functions of B. subtilis BSn5, and can help the strains maintain their activity in the presence of Cr(VI). More importantly, the relative capacity and intensity of Cr(VI) and total Cr removal by B. subtilis BSn5 in the presence of hematite were higher than that in the absence of hematite. The enhancement effect could be associated with their mineral adsorption, biosorption, Fe(II) reduction, bioreduction and immobilization functions. This study demonstrates the possibility of reducing the toxicity of Cr(VI) and enhancing the Cr(VI) removal efficiency in contaminated environments using a combination of hematite and B. subtilis BSn5.

Uranium biosorption from aqueous solution by the submerged aquatic plant Hydrilla verticillata.

The biosorption characteristics of U(VI) from aqueous solution onto a nonliving aquatic macrophyte, Hydrilla verticillata (dry powder), were investigated under various experimental conditions by using batch methods. Results showed that the adsorption reached equilibrium within 60 min and the experimental data were well fitted by the pseudo-first-order kinetic model. U(VI) adsorption was strongly pH dependent, and the optimum pH for U(VI) removal was 5.5. Isotherm adsorption data displayed good correlation with the Langmuir model, with a maximum monolayer adsorption capacity of 171.52 mg/g. Thermodynamic studies suggested that U(VI) adsorption onto H. verticillata was an exothermic and spontaneous process in nature. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that the amino and hydroxyl groups on the algal surface played an important role in U(VI) adsorption. The mechanisms responsible for U(VI) adsorption could involve electrostatic attraction and ion exchange. In conclusion, H. verticillata biomass showed good potential as an adsorption material for the removal of uranium contaminants in aqueous solution.

Uranium biosorption from aqueous solution onto Eichhornia crassipes.

Batch experiments were conducted to investigate the biosorption of U(VI) from aqueous solutions onto the nonliving biomass of an aquatic macrophyte Eichhornia crassipes. The results showed that the adsorption of U(VI) onto E. crassipes was highly pH-dependent and the best pH for U(VI) removal was 5.5. U(VI) adsorption proceeded rapidly with an equilibrium time of 30 min and conformed to pseudo-second-order kinetics. The Langmuir isotherm model was determined to best describe U(VI) biosorption with a maximum monolayer adsorption capacity of 142.85 mg/g. Thermodynamic calculation results indicated that the U(VI) biosorption process was spontaneous and endothermic. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis implied that the functional groups (amino, hydroxyl, and carboxyl) may be responsible for the U(VI) adsorption process, in which the coordination and ion exchange mechanisms could be involved. We conclude that E. crassipes biomass is a promising biosorbent for the removal of uranium pollutants.

Removal of Pb(II) by adsorption onto Chinese walnut shell activated carbon.

The excessive discharge of Pb(II) into the environment has increasingly aroused great concern. Adsorption is considered as the most effective method for heavy metal removal. Chinese walnut shell activated carbon (CWSAC) was used as an adsorbent for the removal of Pb(II) from aqueous solution. Batch experiments were conducted by varying contact time, temperature, pH, adsorbent dose and initial Pb(II) concentration. Adsorption equilibrium was established within 150 min. Although temperature effect was insignificant, the Pb(II) adsorption was strongly pH dependent and the maximum removal was observed at pH 5.5. The Pb(II) removal efficiency increased with increasing CWSAC dosage up to 2.0 g/L and reached a maximum of 94.12%. Langmuir and Freundlich adsorption isotherms were employed to fit the adsorption data. The results suggested that the equilibrium data could be well described by the Langmuir isotherm model, with a maximum adsorption capacity of 81.96 mg/g. Adsorption kinetics data were fitted by pseudo-first- and pseudo-second-order models. The result indicated that the pseudo-first-order model best describes the adsorption kinetic data. In summary, CWSAC could be a promising material for the removal of Pb(II) from wastewater.

Acute toxic effects of three pesticides on Pseudomonas putida monitored by microcalorimeter.

A series of calorimetric experiments were performed to investigate the toxic effects of beta-cypermethrin (BCP), bensulfuron-methyl (BSM) and prometryne (PM) on Pseudomonas putida (P. putida). The metabolic action of P. putida on the three pesticides was studied by obtaining power-time curves. The growth of P. putida was inhibited completely in each case when the concentrations of pesticides were up to 80 micro g mL(- 1). The relationships between the inhibitory ratio (k) and doses of contaminants were approximately linear for the three pesticides. The total heat dissipated per milliliter (Q(total)) for the pesticides decreased during the course of the experiment. The OD(600) of P. putida growth in the absence and presence of pesticides was also obtained. The power-time curves of P. putida growth coincided with its turbidity curves. This elucidates that microcalorimetric method agrees well with the routine microbiological method. Among these three pesticides, BSM was found to be the most toxic with an IC(50) of 19.24 micro g mL(- 1) against P. putida. PM exhibited moderate virulence with an IC(50) of 27.86 micro g mL(- 1) and BCP had the lowest toxicity with an IC(50) of 39.64 micro g mL(- 1).

Evaluation of solvent tolerance of microorganisms by microcalorimetry.

Solvent tolerance is important because it allows microorganisms to grow at high concentrations of organic solvents. Organisms capable of surviving under these extreme conditions have great application in bioremediation of contaminated sites. In our study, four strains of Pseudomonas sp. B1 and J2, Acinetobacter sp. B2 and J6 which were isolated from the activated sludge were used to evaluate the solvent tolerance by microcalorimetry. The strains B2 and J2 showed high tolerance to organic solvent as they could grow well in the medium containing 10 vol% of benzene and 70 vol% of toluene, respectively. The higher the growth rate constant, the higher the solvent tolerance of the strains isolated. The microbial growths obtained by microcalorimetry were in good agreement with the results determined by OD(600). The decrease in growth rate constant and the change in total thermal effect in the presence of organic solvents were in agreement with the data reported in the literatures. Strains B1 and B2 degraded about 67% and 94% of 0.1 vol% benzene within 72 h in a medium with benzene as the sole carbon source, respectively. Strains J2 and J6 degraded approximately 92% and 85% of 0.1 vol% toluene within 72 h, respectively. The related degradation genes detected in previous study in these strains highlight an important potential use of those bacteria for the clean-up of benzene and toluene in the environment.

Investigation of the toxic effect of cadmium on Candida humicola and Bacillus subtilis using a microcalorimetric method.

In this study, the technique of microcalorimetry based on heat-output by aerobic bacterial respiration was explored to evaluate the toxic effect of cadmium on Candida humicola, Bacillus subtilis, singularly or in a mixture of both. Power-time curves of the growth metabolism of C. humicola and B. subtilis and the effect of Cd(2+) were studied using the TAM III (the third generation thermal activity monitor) multi-channel microcalorimetric system, isothermal mode, at 28 degrees C. The differences in shape of the power-time curves and the thermodynamic and kinetic characteristics of microorganisms growth were compared. The effect of cadmium added into microorganism would significantly reduce the life cycle and change the thermal effect of microbial metabolic process with different concentrations of Cd(2+). The experimental results revealed that at the same concentration, the sequence of inhibitory ratio (I) and maximum thermal power (P(max)) of the Cd(2+) was: mixed microorganisms>C. humicola>B. subtilis. The sequence of total thermal effect (Q(total)) and growth rate constant (k) is mixed microorganisms>B. subtilis>C. humicola. These results are important to further studies of the physiology and pharmacology of C. humicola and B. subtilis and may support the theory of restoring contaminated soil.