Janette Tourney

Physical and chemical effects of extracellular polymers (EPS) on Zn adsorption to Bacillus licheniformis S-86.

This study investigated Zn adsorption to an extracellular polymeric substance (EPS)-producing bacterial strain, Bacillus licheniformis S-86. Batch metal adsorption experiments and spectroscopic (EXAFS) analysis were conducted using both native (EPS-covered) cells and EPS-free cells in order to assess the contribution made by EPS to metal adsorption by this strain. Thermodynamic modelling of the macroscopic adsorption data indicated that Zn complexation to both native and EPS-free cells was predominantly to carboxyl (pK(a)5.3-5.4) and phosphate (pK(a)7.4-7.5) functional groups, but with some adsorption to phosphodiester (pK(a)3.3-3.4) groups also evident. EXAFS analysis shows Zn-carboxyl complexation, but possibly with a significant contribution from a second, phosphate functional group. Apparently, EPS removal does not affect the metal adsorption capacity at the metal: biomass ratios used here. As the concentration of carboxyl and phosphate functional groups is only slightly affected by EPS extraction, complexation to these functional groups explains why EPS removal does not reduce the amount of Zn adsorbed by the cells. It was also observed that EPS production induces aggregation of cells in suspension. This may reduce the cell surface area available for metal adsorption, thus counteracting any greater availability of metal-complexing ligands in the EPS layer compared to an EPS-free cell surface. Furthermore, the EPS layer appears to be the major source of dissolved organic carbon (DOC) released to solution during the metal adsorption experiments. This DOC may reduce metal binding to the cell surfaces by acting as a competing complexing ligand. These observations have implications for industrial application of biofilms and suggest that over-production of EPS in bio-reactors may reduce the metal removal efficiency of the biomass.

Remediation of a historically Pb contaminated soil using a model natural Mn oxide waste

A natural Mn oxide (NMO) waste was assessed as an in situ remediation amendment for Pb contaminated sites. The viability of this was investigated using a 10 month lysimeter trial, wherein a historically Pb contaminated soil was amended with a 10% by weight model NMO. The model NMO was found to have a large Pb adsorption capacity (qmax 346±14 mg g(-1)). However, due to the heterogeneous nature of the Pb contamination in the soils (3650.54-9299.79 mg kg(-1)), no treatment related difference in Pb via geochemistry could be detected. To overcome difficulties in traditional geochemical techniques due to pollutant heterogeneity we present a new method for unequivocally proving metal sorption to in situ remediation amendments. The method combines two spectroscopic techniques; namely electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). Using this we showed Pb immobilisation on NMO, which were Pb free prior to their addition to the soils. Amendment of the soil with exogenous Mn oxide had no effect on microbial functioning, nor did it perturb the composition of the dominant phyla. We conclude that NMOs show excellent potential as remediation amendments.

The effect of ionic strength on the electrophoretic mobility and protonation constants of an EPS-producing bacterial strain

The production of extracellular polymeric substances (EPS) by bacteria significantly alters the physical structure of the cell wall-solution interface, potentially affecting cell surface reactivity and colloidal (transport) properties of the cells. This study investigated the effect of the EPS layer on the electrostatic properties of the cell surface by conducting electrophoretic mobility (EM) analysis and potentiometric titrations at ionic strengths of 0.001 M, 0.01 M and 0.1 M, using both native cells, with the EPS-layer intact, and EPS-free cells of the gram-positive thermophile, Bacillus licheniformis S-86. Electrophoretic mobility measurements indicated that the isoelectric point for both cell types was below pH 2. At low ionic strength (0.001 M), expansion of the EPS layer causes the EM of the native cells to have a smaller magnitude than that of the EPS-free cells. As ionic strength increases, this effect diminishes and at 0.1M the native cells have a higher EM than the EPS-free cells, which indicates that there is a relatively high charge density in the EPS layer. Higher total site concentrations obtained using potentiometric titration data modelling for the native cells are in agreement with the electrophoretic mobility data, and indicate a higher proton-active site density in the EPS layer compared to the EPS-free cell wall. The results of data modelling for titrations conducted at all three ionic strength values showed that there are no systematic changes in deprotonation constants or site concentrations as a function of ionic strength, indicating that the use of a non-electrostatic model is justified for this EPS-producing bacterial strain.

Oxidation of anthracene using waste Mn oxide minerals : the importance of wetting and drying sequences

PAHs are a common problem in contaminated urban soils due to their recalcitrance. This study presents results on the oxidation of anthracene on synthetic and natural Mn oxide surfaces. Evaporation of anthracene spiked Mn oxide slurries in air results in the oxidation of 30% of the anthracene to anthraquinone. Control minerals, quartz and calcite, also oxidised a small but significant proportion of the anthracene (4.5% and 14% conversion, respectively) when spiked mineral slurries were evaporated in air. However, only Mn oxide minerals showed significant anthracene oxidation (5-10%) when evaporation took place in the absence of oxygen (N2 atmosphere). In the fully hydrated systems where no drying took place, natural Mn oxides showed an increase in anthracene oxidation with decreasing pH, with a conversion of 75% anthracene at pH 4. These results show both acidification and drying favor the oxidation of anthracene on Mn oxide mineral surfaces. It has also been demonstrated that non-redox active mineral surfaces, such as calcite, may play a role in contaminant breakdown during wetting and drying sequences. Given that climate changes suggest that wetting and drying sequences are likely to become more significant these results have important implications for contaminated land remediation technologies.

Mn oxide as a contaminated-land remediation product

Natural Mn oxides are an important component of biogeochemical cycles in many environmental settings. Mn oxides are strong oxidizing agents, facilitating the breakdown of organic contaminants and enhancing humification of soil organic matter. Interactions with metals and radionuclides, including surface adsorption, sequestration and oxidation can lead to incorporation of metals into insoluble mineral phases and a consequent reduction in bioavailability of …

Bacterial EPS as a mediator of calcium carbonate morphology and polymorphism

Biologically influenced mineralization either on the surfaces of, or in close proximity to bacterial cells may produce minerals that display distinct mineralogical or morphological features as a consequence of the microbial influence on the precipitation process. Characterizing such distinguishing features could potentially facilitate identification of early life in the geological record. Many recent investigations have aimed to identify unique …