Xingmin Rong

Interaction of Pseudomonas putida with kaolinite and montmorillonite: A combination study by equilibrium adsorption, ITC, SEM and FTIR

Equilibrium adsorption along with isothermal titration calorimetry (ITC), Fourier transform infrared spectra (FTIR) and scanning electron microscopy (SEM) techniques were employed to investigate the adsorption of Pseudomonas putida on kaolinite and montmorillonite. A higher affinity as well as larger amounts of adsorption of P. putida was found on kaolinite. The majority of sorbed bacterial cells (88.7%) could be released by water from montmorillonite, while only a small proportion (9.3%) of bacteria desorbed from kaolinite surface. More bacterial cells were observed to form aggregates with kaolinite, while fewer cells were within the larger bacteria-montmorillonite particles. The sorption of bacteria on kaolinite was enthalpically more favorable than that on montmorillonite. Based on our findings, it is proposed that the non-electrostatic forces other than electrostatic force play a more important role in bacterial adsorption by kaolinite and montmorillonite. Adsorption of bacteria on clay minerals resulted in obvious shifts of infrared absorption bands of water molecules, showing the importance of hydrogen bonding in bacteria-clay mineral adsorption. The enthalpies of -4.1+/-2.1 x 10(-8) and -2.5+/-1.4 x 10(-8)mJ cell(-1) for the adsorption of bacteria on kaolinite and montmorillonite, respectively, at 25 degrees C and pH 7.0 were firstly reported in this paper. The enthalpy of bacteria-mineral adsorption was higher than that reported previously for bacteria-biomolecule interaction but lower than that of bacterial coaggregation. The bacteria-mineral adsorption enthalpies increased at higher temperature, suggesting that the enthalpy-entropy compensation mechanism could be involved in the adsorption of P. putida on clay minerals. Data obtained in this study would provide valuable information for a better understanding of the mechanisms of mineral-microorganism interactions in soil and associated environments.

Pseudomonas putida adhesion to goethite: Studied by equilibrium adsorption, SEM, FTIR and ITC

Equilibrium adsorption along with scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and isothermal titration calorimetry (ITC) techniques were employed to investigate the adhesion of Pseudomonas putida on goethite. The adhesion isotherm revealed the high affinity of P. putida for goethite. The SEM analysis also showed a tight association between bacteria and mineral particles. Larger amounts of adhesion of bacteria on goethite were observed at pH lower than the isoelectric point (IEP) of goethite. The bacterial adhesion increased with increasing concentration of K(+). The calorimetric results demonstrated that the P. putida-goethite adhesion was an exothermic process. The adhesion enthalpy increased with increasing pH and concentrations of electrolyte. The increase of the negative enthalpy with increment of temperature indicated that the bacteria-goethite adhesion was an enthalpy-driven process. Electrostatic interactions and hydrogen bonding were considered to contribute mainly to the adhesion of bacterial adhesion on goethite. The data obtained in this study would provide valuable information for a better understanding of the mechanisms of mineral-microorganism interactions in soil and associated environments.

Binding characteristics of copper and cadmium by cyanobacterium Spirulina platensis.

Cyanobacteria are promising biosorbent for heavy metals in bioremediation. Although sequestration of metals by cyanobacteria is known, the actual mechanisms and ligands involved are not very well understood. The binding characteristics of Cu(II) and Cd(II) by the cyanobacterium Spirulina platensis were investigated using a combination of chemical modifications, batch adsorption experiments, Fourier transform infrared (FTIR) spectroscopy and X-ray absorption fine structure (XAFS) spectroscopy. A significant increase in Cu(II) and Cd(II) binding was observed in the range of pH 3.5-5.0. Dramatical decrease in adsorption of Cu(II) and Cd(II) was observed after methanol esterification of the nonliving cells demonstrating that carboxyl functional groups play an important role in the binding of metals by S. platensis. The desorption rate of Cu(II) and Cd(II) from S. platensis surface was 72.7-80.7% and 53.7-58.0% by EDTA and NH(4)NO(3), respectively, indicating that ion exchange and complexation are the dominating mechanisms for Cu(II) and Cd(II) adsorption. XAFS analysis provided further evidence on the inner-sphere complexation of Cu by carboxyl ligands and showed that Cu is complexed by two 5-membered chelate rings on S. platensis surface.

Microcalorimetric and potentiometric titration studies on the adsorption of copper by P. putida and B. thuringiensis and their composites with minerals

In order to have a better understanding of the interactions of heavy metals with bacteria and minerals in soil and associated environments, isothermal titration calorimetry (ITC), potentiometric titration and equilibrium sorption experiments were conducted to investigate the adsorption behavior of Cu(II) by Bacillus thuringiensis, Pseudomonas putida and their composites with minerals. The interaction of montmorillonite with bacteria increased the reactive sites and resulted in greater adsorption for Cu(II) on their composites, while decreased adsorption sites and capacities for Cu(II) were observed on goethite-bacteria composites. A gram-positive bacterium B. thuringiensis played a more important role than a gram-negative bacterium P. putida in determining the properties of the bacteria-minerals interfaces. The enthalpy changes (DeltaH(ads)) from endothermic (6.14 kJ mol(-1)) to slightly exothermic (-0.78 kJ mol(-1)) suggested that Cu(II) is complexed with the anionic oxygen ligands on the surface of bacteria-mineral composites. Large entropies (32.96-58.89 J mol(-1) K(-1)) of Cu(II) adsorption onto bacteria-mineral composites demonstrated the formation of inner-sphere complexes in the presence of bacteria. The thermodynamic data implied that Cu(II) mainly bound to the carboxyl and phosphoryl groups as inner-sphere complexes on bacteria and mineral-bacteria composites.

Isothermal Microcalorimetry： A Review of Applications in Soil and Environmental Sciences

Abstract Isothermal microcalorimetry provides thermodynamic and kinetic information on various reactions and processes and is thereby a powerful tool to elucidate their mechanisms. Certain improvement in isotherma! microcalorimetry with regard to the studies on soil and environmental sciences is briefly described. This review mainly focuses on the use of microcalorimetry in the determination of soil microbial activity, monitoring the toxicity and biodegradation of soil organic pollutants, the risk evaluation of metals and metalloids, the heat effect of ion exchange and adsorption in soil, and environmental researches. Promising prospects for the applications of the technique in the field are also discussed.

Cd(II) Sorption on Montmorillonite-Humic acid-Bacteria Composites

Soil components (e.g., clays, bacteria and humic substances) are known to produce mineral-organic composites in natural systems. Herein, batch sorption isotherms, isothermal titration calorimetry (ITC), and Cd K-edge EXAFS spectroscopy were applied to investigate the binding characteristics of Cd on montmorillonite(Mont)-humic acid(HA)-bacteria composites. Additive sorption and non-additive Cd(II) sorption behaviour is observed for the binary Mont-bacteria and ternary Mont-HA-bacteria composite, respectively. Specifically, in the ternary composite, the coexistence of HA and bacteria inhibits Cd adsorption, suggesting a “blocking effect” between humic acid and bacterial cells. Large positive entropies (68.1 ~ 114.4 J/mol/K), and linear combination fitting of the EXAFS spectra for Cd adsorbed onto Mont-bacteria and Mont-HA-bacteria composites, demonstrate that Cd is mostly bound to bacterial surface functional groups by forming inner-sphere complexes. All our results together support the assertion that there is a degree of site masking in the ternary clay mineral-humic acid-bacteria composite. Because of this, in the ternary composite, Cd preferentially binds to the higher affinity components-i.e., the bacteria.

Effects of low-molecular-weight organic ligands and phosphate on adsorption of Pseudomonas putida by clay minerals and iron oxide.

Adsorption of Pseudomonas putida on kaolinite, montmorillonite and goethite was studied in the presence of organic ligands and phosphate. Citrate, tartrate, oxalate and phosphate showed inhibitive effect on P. putida adsorption by three minerals in a broad range of anion concentrations. The highest efficiencies of the four ligands in blocking the adsorption of P. putida on goethite, kaolinite and montmorillonite were 58-90%, 35-76% and 20-48%, respectively. The ability of organic ligands in prohibiting the binding of P. putida cells to the minerals followed the sequence of citrate>tartrate>oxalate>acetate. The significant suppressive effects on P. putida adsorption were ascribed to the increased negative charges by adsorbed ligands and the competition of ligands with bacterial surface groups for binding sites. The inhibitive effects on P. putida adsorption by organic ligands were also dependent on the steric hindrance of the molecules. Acetate presented promotive effect on P. putida adsorption by kaolinite and goethite at low anion concentrations. The results obtained in this study suggested that the adsorption of bacteria in soils especially in the rhizosphere can significantly be impacted by various organic and inorganic anions.

Soil Colloids and Minerals Modulate Metabolic Activity of Pseudomonas putida Measured Using Microcalorimetry

Substantial interactions of microbes with soil particles present fundamental influences on microbial activities relevant to a series of biogeochemical processes. However, how soil surface-active particles modulate microbial metabolism has received scant attention. The extent to which composition of soil colloids alter the metabolism is not well addressed. This work examined the impacts of soil colloids and minerals on the metabolic activity of Pseudomonas putida using microcalorimetry and carbon utilization. The results showed that montmorillonite remarkably improved metabolic activity of P. putida, whereas kaolinite, goethite and soil colloids significantly inhibited the activity. Humus may weaken the inhibition of soil colloids on bacterial metabolism via interfacial interaction rather than nutrient supplements. Soils bearing higher amount of kaolinite and iron oxide may have greater depression on bacterial activity. The thermodynamic method provides different and complementary information to that from other techniques in characterizing microbial activities. The quantity and affinity for the adhesion of bacteria onto soil components together with the detoxification of metabolites were assigned to the modifications of bacterial activities.

Effects of Temperature, pH and Salt Concentrations on the Adsorption of Bacillus subtilis on Soil Clay Minerals Investigated by Microcalorimetry

Adsorption of microorganisms on minerals is a ubiquitous interfacial phenomenon in soil. Knowledge of the extent and mechanisms of bacterial adsorption on minerals is of great agronomic and environmental importance. This study examined adsorption of Bacillus subtilis on three common minerals in soils such as kaolinite, montmorillonite and goethite under various environmental conditions. Isothermal titration calorimetry (ITC) was used to investigate the effects of temperature (20, 30, and 40°C), pH (5.0, 7.0, and 9.0) and KNO3 concentration (0.001, 0.01, and 0.1 mol L−1) on the adsorption by direct measurement of enthalpies. The results revealed that the adsorption process in all the mineral systems were exothermic, with the enthalpy changes (ΔHads ) ranging from −52 to −137, −33 to −147, and −53 to −141 kJ kg−1 (dry weight of adsorbed bacteria) for kaolinite, montmorillonite, and goethite, respectively. No obvious dependence of ΔHads on temperature was observed. The heat release for all the systems generally declined with pH and decrease of salt concentration, which can be explained by the variations of hydrophobicity and electrostatic force with pH or salt concentration. The largest decrease was found for goethite among the three minerals from pH 5.0 to 7.0, suggesting that electrostatic attraction may play a more important role in bacterial adsorption on this mineral. The ΔHads values for all the minerals became nearly the same at pH 9.0, indicating that the same force probably hydrophobicity governing the adsorption for the minerals in alkaline environment. It is assumed that acidic or saline soils and the associated environments favor the adsorption of B. subtilis on clay minerals. In addition, the negative enthalpies expressed as kJ kg−1 (carbon) revealed an energy flow into the environment accompanied by the carbon adsorption on the minerals in soil.

In situ ATR-FTIR study on the adhesion of Pseudomonas putida to Red soil colloids

PurposeBacterial adhesion to soil particles is fundamentally important in mineral weathering, organic matter degradation, heavy metal transformation, and fate of pollutants. However, the adhesion mechanism between bacteria and soil colloids under continuous flow systems in the natural environments remains unknown.Materials and methodsThe kinetics of Pseudomonas putida cellular adsorption and desorption on Red soil colloid films under controlled flow systems were examined using in situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Derjaguin–Landau–Verwey–Overbeek (DLVO) and non-DLVO interactions were employed to elucidate the cellular adsorption and desorption kinetics.Results and discussionIn situ ATR-FTIR spectroscopy can be used effectively to investigate the kinetics of bacterial adhesion to a soil colloid deposit. Surface proteins may be involved in the bacterial adhesion to soil colloids. The adsorption followed pseudo-first-order kinetic equation. High adsorption rate constant and great saturation coverage of adsorbed bacteria were found at high ionic strengths in dynamic systems.ConclusionsP. putida bacterial cellular adsorption on the soil colloid deposit was irreversible in a wide range of ionic strengths under controlled flow systems. The less reversible adhesion was probably attributed to the DLVO predicted deep secondary energy minima together with non-DLVO factors including polymer bridging, local charge heterogeneities, surface roughness, and Lewis acid–base interactions.