Huilun Chen

Short-time effect of heavy metals upon microbial community activity

Microcalorimetry was applied to assess and compare the toxic effect of heavy metals, such as As, Cu, Cd, Cr, Co, Pb and Zn, on the soil microbial activities and community. About 1.0 g soil spiked 5.0mg glucose and 5.0mg ammonium sulfate, the microbial activities were recorded as power-time curves, and their indices, microbial growth rate constant k, total heat evolution Q(T), metabolic enthalpy Delta H(met) and mass specific heat rate J(Q/S), were calculated. Comparing these thermodynamic parameters associated with growth yield, a general order of toxicity to the soil was found to be Cr>Pb>As>Co>Zn>Cd>Cu. When soil was exposed to heavy metals, the amount of bacteria and fungi decreased with the incubation time, and the bacterial number diminished sharply. It illustrates that fungi are more tolerant, and bacteria-fungi ratio would be altered under metal stress. To determine the status of the glucose consumed, a glucose biosensor with eggshell membrane was used to measure the remaining glucose in soil sample. Results showed that the time at which glucose was consumed completely was agreed with the microcalorimetric time to a large extent, and depended on the toxicity of heavy metals as well.

Comparative toxicity of chlorpyrifos and its oxon derivatives to soil microbial activity by combined methods.

The inhibitory effects of the pesticide Chlorpyrifos (CPF) and its oxon derivative (CPO) on soil microbial activity were evaluated through the measurement of metabolic parameters and the microbial urease enzyme. The thermodynamic parameters related to microbial activity were measured and recorded as power-time curves. Microbial growth rate constant k, total heat evolution Q(T), metabolic enthalpy DeltaH(met), mass specific heat rate J(Q/S), microbial biomass C and inhibitory ratio I were calculated. They showed the linear relationship with doses of CPF and CPO. Thereinto, the linear correlations, k versus biomass C and DeltaH(met) versus biomass C, elucidated that k and DeltaH(met) were growth yield dependent. In this work, 20% inhibitory ratio IC(20) was obtained with 9.8 microg g(-1) for CPF and 0.37 microg g(-1) CPO, meaning that the acute toxicity of CPO was 26 times that of CPF, since the CPO had more potent toxicity to living organism due to its active functional group. Comparing the change tendency of DeltaH(met) and other parameter, the values almost kept constant when exposure to CPF (<5.0 microg g(-1)). It illustrates that individual reacted to stress resulted from environment change by shifting resources from other biological activities (such as reproduction or growth) toward survival to some extent. Urease activity responses in relation to the CPF and CPO exposure were observed and consistent with above thermodynamic parameters.

Study on the toxic effects of diphenol compounds on soil microbial activity by a combination of methods

Microcalorimetric technique based on heat-output measurement, direct microorganism counting and enzymatic activity determination, have been explored to evaluate the toxic effects of diphenol species (catechol, resorcinol, and hydroquinone) on soil microbial activity. The thermokinetic parameters including growth rate constant (k), inhibitory ratio, half inhibitory concentration and total thermal effect (Q(total)), were calculated and compared using the data obtained from the power-time curves of the microcalorimeter. It was found that addition of high concentrations of diphenol compounds to the soil samples resulted in low microorganism counts. The trend of the number of cultivable microorganisms with increasing concentration of diphenols was similar to specific growth rate k. It appeared that the higher the water soluble carbon (WSC) content, the higher the Q(total) value. The low dehydrogenase and beta-glucosidase found in the soils treated by catechol and hydroquinone was possibly due to their low WSC concentration and high inhibitory effects, respectively. The results reveal the toxicity of the three diphenols in a descending sequence: hydroquinone, resorcinol and catechol. The combination of the three methods is a more comprehensive toxicological investigation of a complex microbiological system. Microcalorimetry is for studying the metabolic growth of microorganisms, the plate counting method is for quantifying the real microbial growth, and the soil enzyme activity is for assessing the intracellular and extracellular activity of microbial biomass. Our proposed methods can provide toxicological information of diphenols to soil microbes from the metabolic, microbial and biochemical point of views which are consistent with and correlated to each other.

Toxicity of three phenolic compounds and their mixtures on the gram-positive bacteria Bacillus subtilis in the aquatic environment

Although phenolic compounds are intensively studied for their toxic effects on the environment, the toxicity of catechol, resorcinol and hydroquinone mixtures are still not well understood because most previous bioassays are conducted solely using single compound based on acute tests. In this work, the adverse effect of individual phenolic compounds (catechol, resorcinol and hydroquinone) and the interactive effect of the binary and tertiary mixtures on Bacillus subtilis (B. subtilis) using microcalorimetric method were examined. The toxicity of individual phenolic compounds follows the order catechol>resorcinol>hydroquinone with their respective half inhibitory concentration as 437, 728 and 934 microg mL(-)(1). The power-time curve of B. subtilis growth obtained by microcalorimetry is in complete agreement with the change in turbidity of B. subtilis against time, demonstrating that microcalorimetric method agrees well with the routine microbiological method. The toxicity data obtained from phenolic compound mixtures show that catechol and hydroquinone mixture possess synergistic effect while the other mixtures display additive joint actions. Furthermore, the concentration addition (CA) and independent action (IA) models were employed to predict the toxicities of the phenolic compounds. The experimental results of microcalorimetry show no significant difference on the toxicity of the phenolic compound mixtures from that predicted by CA. However, IA prediction underestimated the mixture effects in all the experiments.

A combination method to study microbial communities and activities in zinc contaminated soil.

Zinc (Zn) plays a special role in soil ecology and fertility because it can support the growth of soil organisms or inhibit their growth depending on its concentrations. In this work, the effects of different concentrations of Zn on soil microbial communities and activities were analyzed by loading five different doses of Zn (160-6000 microg g(-1)) into a wheat surface soil. The microbial metabolic process revealed a significant bimodal pattern at high concentrations of Zn (>1920 microg g(-1)). This phenomenon suggested that soil microorganisms were very sensitive to zincous poisoning. A variety of soil quality properties were also measured and assessed. The results showed slower bacterial growth in soil cultures polluted with high levels of Zn. In addition, two kinds of fungi were identified by morphology and glomalin-related soil protein content in the Zn-contaminated soil. The growth of the first kind was inhibited with increase in Zn concentration. By contrast, the second kind could survive and continue to grow with increasing doses of Zn at 160-1920 microg g(-1) and its growth began to decline with further increase in Zn concentration. Finally, the fungus could not survive at very high (6000 microg g(-1)) Zn concentration. In this work, we conclude that soil microbial communities and activities can adapt to Zn pollution to a certain extent.

Oxidative decomposition of atrazine in water in the presence of hydrogen peroxide using an innovative microwave photochemical reactor.

The simultaneous application of microwave (MW) power and UV light leads to improved results in photochemical processes. This study investigates the oxidative decomposition of atrazine in water using an innovative MW and UV photochemical reactor, which activates a chemical reaction with MW and UV radiation using an immersed source without the need for a MW oven. We investigated the influence of reaction parameters such as initial H(2)O(2) concentrations, reaction temperatures and applied MW power and identified the optimal conditions for the oxidative decomposition of atrazine. Atrazine was completely degraded by MW/UV/H(2)O(2) in a very short time (i.e. t(1/2) = 1.1 min for 20.8 mg/L in optimal conditions). From the kinetic study, the disappearance rate of atrazine can be expressed as dX/dt = k(PH)[M](0)(b-X)(1-X), where b ≡ [H(2)O(2)](0)/[M](0)+k(OH)[·OH]/k(PH)[M](0), and X is the atrazine conversion, which correlates well with the experimental data. The kinetic analysis also showed that an indirect reaction of atrazine with an OH radical is dominant at low concentrations of H(2)O(2) and a direct reaction of atrazine with H(2)O(2) is dominant when the concentration of H(2)O(2) is more than 200 mg/L.

Impact of beta-cypermethrin on soil microbial community associated with its bioavailability: A combined study by isothermal microcalorimetry and enzyme assay techniques

In this study, an isothermal microcalorimetric technique has been used to show that beta-cypermethrin (CYP) had no significant effect (p > 0.05) on soil microbial activity at 80 μg g(-1) soil. Our soil enzyme data indicated that beta-CYP ranging 10-80 μg g(-1) soil had no significant effect (p > 0.05) on soil enzyme activities such as β-glucosidase, urease, acid-phosphatase, and dehydrogenase. Therefore, our results infer that beta-CYP would not pose severe toxicity to soil microbial community, but its toxic level may vary greatly with environment that associates with its increase in bioavailability: the level in soil (at μg g(-1)) < the level in sediment (varying from μg g(-1) to μg L(-1))<the level in water (at μg L(-1)). The comparison of the results of solvent volatilization on soil microbial activity has shown that the acetone-treated sample had no significant difference with the control (p > 0.05). These results suggest that the heavy application of beta-CYP may not cause damage to soil microbial community which is very different from its high toxicity to the aquatic organism.

Isolation and characterization of a novel phenanthrene (PHE) degrading strain Psuedomonas sp. USTB-RU from petroleum contaminated soil.

The phenanthrene degrading novel bacterium strain USTB-RU was isolated from petroleum contaminated soil in Dagan oilfield, southeast of Tianjin, northeast China. The novel isolate was identified as Pseudomonas sp. USTB-RU on the basis of morphological, physicochemical characteristics and analysis of 16S rDNA gene sequence. The strain could degrade 86.65% of phenanthrene at an initial concentration of 100 mg L(-1) in 8 days and identified intermediate metabolite evident the biodegradation of phenanthrene through protocatechuate metabolic pathway. The strain showed the potential to produce surface-active compounds that may have caused for the resulted efficient biodegradation through enhancing the substrate bioavailability. The results highlighted that the adaptability of USTB-RU to grow in a range of temperature, pH and potential to utilize various commonly co-exist pollutants in contaminated site other than phenanthrene as sole carbon and energy source. Further, susceptibility of the strain for the tested antibiotics inferred the possibility to absence of risk of spreading drug resistant factor to other indigenous bacteria. Therefore, the isolated novel strain USTB-RU may have a high potential for application in in situ bioremediation of phenanthrene contaminated environment.

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.

Interaction of prometryn to human serum albumin: Insights from spectroscopic and molecular docking studies

Prometryn possesses much potential hazard to environment because of its chemical stability and biological toxicity. Here, the binding properties of prometryn with human serum albumin (HSA) and the protein structural changes were determined under simulative physiological conditions (pH 7.4) by multispectroscopic methods including fluorescence, UV-vis absorption, Fourier transform infrared (FT-IR) and circular dichroism (CD) spectroscopy, coupled with molecular modeling technique. The result of fluorescence titration suggested that the fluorescence quenching of HSA by prometryn was considered as a static quenching procedure. The negative enthalpy change (ΔH(○)) and positive entropy change (ΔS(○)) values indicated that the binding process was governed mainly by hydrophobic interactions and hydrogen bonds. The site marker displacement experiments suggested the location of prometryn binding to HSA was Sudlows site I in subdomain IIA. Furthermore, molecular docking studies revealed prometryn can bind in the large hydrophobic activity of subdomain IIA. Analysis of UV-vis absorption, synchronous fluorescence, CD and FT-IR spectra demonstrated that the addition of prometryn resulted in rearrangement and conformational alteration of HSA with reduction in α-helix and increases in β-sheet, β-turn and random coil structures. This work provided reasonable model helping us further understand the transportation, distribution and toxicity effect of prometryn when it spreads into human blood serum.