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No description available.

No description available.

No description available.

Cyanobacterial secondary metabolites, microcystins (MC) and nodularin (NOD) have become common contaminants in most aquatic ecosystems over recent years presenting a hazard to animal and human health. Unfortunately, these chemically diverse peptide hepatotoxins remain a challenge to most conventional water treatments due to their stable cyclic structures. Over recent years, bioremediation of MC and NOD has become one of the most exciting areas that holds promise for a successful and cost effective solution for water treatment process. The current work presents the biodegradation of MCs and NOD by bacterial isolates from three different bacteria genus Arthrobacter, Brevibacterium and Rhodococcus belonging to Actinobacteria. A total of five isolates representing the three genera have demonstrated an overall metabolism of MC-LR, -LF, -LY, -LW, -RR and NOD in a Biolog MT2 assay. Subsequently, these bacteria were reported to degrade the range of toxins in a separate batch experiment. The bacterial degradation rate of the above cyanobacterial peptides were found to decrease with the multiple subculturing of the bacteria. However, a rapid degradation was discovered when the bacteria were re-exposed to MC or other prokaryotic peptides demonstrating an inducible bacterial biodegradation. Utilising latest molecular biology techniques, the gene responsible for production of MC degrading enzymes was successfully elucidated and its activity was evaluated. Analysis of the degradation products of MC-LR revealed a glutathione conjugate detoxification mechanism involved during the degradation of MC-LR by Rhodococcus sp. (C1). A novel MC degradation pathway was proposed. Further studies were suggested to fully characterise the degradation pathway and to evaluate the MC detoxification mechanism in bacteria.

In this project, a tool-kit based upon the use of genetically modified luminescent bacterial biosensors was applied to support the remediation of a site with a history of BTEX contamination. The luminescence response from the biosensors indicated that there were high levels of toxicity on one area of the site, which may have resulted in a constraint to microbial activity. Treatment of samples by air sparging and activated charcoal resulted in a reduction in sample toxicity and BTEX availability. These data were used to assist the planning of site remediation strategies. The biosensor suite was then used to predict the potential constraint to BTEX bioremediation of co-contamination with heavy metals. Soils of varying pH were contaminated with zinc and copper to represent a model system. Biosensor analysis indicated that increased metal bioavailability in soils of low pH may affect the ability of a microbial community to degrade toluene. The BTEX degradation capacities of in situ microbial communities on the study site were investigated using biofilm culture units. Results of this work indicated that a different community was isolated from each groundwater well. The largest active biofilms and greatest degradation capacities were found in samples taken from groundwater wells with the highest BTEX concentrations. Biofilm samples were also subjected to molecular analysis, with amplification of 16S sequences achieved in all samples. Degradative genes, tod and bed, were only successfully amplified from samples taken from groundwater wells with the highest BTEX concentrations.

Contamination of the environment by petrogenic hydrocarbons continues to pose a threat to marine biota. Studies into the effects of hydrocarbon contamination have mainly been directed at a small number of polycyclic aromatic hydrocarbons (PAHs) that are known to be highly toxic to a wide range of biota. The majority of the hydrocarbons present in sediments and tissues are unresolved by conventional gas chromatography and have received little attention. Studies directed at these unresolved complex mixtures (UCMs) of hydrocarbons have previously identified the monoaromatic fraction as containing toxic UCM compounds. The studies reported herein have explored the toxicity of UCM compounds to marine biota using an effect-directed analysis approach: (i) population-level effects on the amphipod Corophium volutator arising from chronic exposure to UCM hydrocarbon contaminated sediments; (ii) bioaccumulation and depuration of UCM hydrocarbons by the blue mussel, Mytilus edulis using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GCXGC-ToF-MS); and, (iii) the possible trophic transfer of UCM hydrocarbons from contaminated mussels to the predatory shore crab Carcinus maenas. Chronic sediment exposure tests showed that oils dominated by UCM hydrocarbons reduced the growth rate and reproductive success of C. volutator. All fractions of the oils contributed towards the toxicity but the aromatic fraction produced effects at lower nominal sediment concentrations. The aromatic fraction was also responsible for the reduction of mussel filter-feeding clearance rates. Analyses of mussel tissue extracts by GCXGC-ToF-MS revealed that a range of aromatic compounds was rapidly accumulated, but most were readily depurated. Compounds that were more resistant to depuration, including branched alkylbenzenes (BABs), were also found in wild mussel populations previously reported to have poor health status. Tests using a commercially available complex mixture of C12_1B4 ABs confirmed that these compounds were toxic to mussels and were not readily depurated. Crabs that consumed mussels contaminated with BABs were found to behave abnormally, but cellular and physiological effects were not significantly different to control organisms. Crab midgut gland tissues were found to contain low concentrations of BABs and fluorescence from urine suggested that the BABs were metabolised and/or excreted. The results did not support the hypothesis that BABs were likely to biomagnify within the marine food web. The research reported herein supports the hypothesis that environmental UCMs are largely comprised of branched alkylated homologues of known petrogenic hydrocarbons. Of these, the BABs have been shown to bioaccumulate and cause adverse effects via a non-specific narcosis mode of action. Marine environment monitoring and regulatory bodies may benefit from taking into account the concentrations of UCM hydrocarbons, in particular the aromatic UCM, including the BABs.

The first gasworks were developed in the early 19th Century and their usage increased until the 1970's when the manufacture of town gas was phased out owing to the new natural gas supply. Consequently, gasworks often have a long history of potentially contaminative use. The main process utilised on these sites, coal carbonization, produced a broad range of potential contaminants including phenols, benzene, toluene, ethylbenzene and xylene (BTEX), polycyclic aromatic hydrocarbons (P AH's), ammonium, and cyanides. This study has focused largely on ammonium and phenol migration and attenuation in the Chalk aquifer and overlying sediments, following the extensive characterisation of a former gasworks at St Albans, Hertfordshire, UK. Invasive and non-invasive techniques, including borehole construction, enabling core- retrieval, "- and geophysical investigation methods respectively, have been used to characterise the nature and extent of contamination and the possible migration pathways in the Chalk aquifer. Chalk pore-water quality analyses indicate that the aquifer is contaminated at depth, but attenuation of ammonium and phenol is sufficient to reduce .- 'concentrations to an acceptable level in the nearby Holywell Hill pumping station. Concentrations of ammonium, phenols and the BTEX compounds in fissure-derived water beneath the former gasworks are well above drinking water• standards, and long- term monitoring has shown that their distribution is closely related to fluctuations in water levels and changes in pumping regimes at the pumping station. Excavation and drilling work has highlighted the variability in the depth of the Chalk surface over the study area, and this has a significant influence on groundwater flow and contaminant --- distribution. Batch adsorption experiments on unsaturated and saturated zone sediments suggest that _phenol is only adsorbed by topsoil samples owing to the presence of specific fractions of organic matter. Ammonium adsorption was highest in unsaturated zone sediments and is closely related to surface area and cation exchange capacity. Leaching through cores suggests that the Chalk matrix has little potential for the attenuation of ammonium. Biodegradation appears to control the attenuation of phenol in the Chalk.

Based on an understanding of how bacteria attach, grow and detach, new cleaning strategies, are urgently needed by many industries. In addition, a better understanding of microbial processes at surfaces offers opportunities for industrial developments, such as bioremediation, treatment of hazardous waste sites, bio-filtration and forming bio-barriers to protect soil and groundwater from contamination. This work aims to study and develop a model of the interaction energies that exist between a bacteria and mineral surfaces in the initial stages of bacterial adhesion and to compare this model to laboratory assessments of adhesion. The classical DLVO theory developed by Derjaguin-Landau-Verwey-Overbeek consists of two interaction energies (Lifshitz van der Waals and electrostatic double layer), which have been widely applied in colloidal interactions. The extended theory, XDLVO, developed by van Oss adds a consideration of acid base interactions and hydrophobicity effects and is currently the best favoured model for evaluating the behaviour of interactions between bacteria and surfaces in understanding bacterial adhesion either to encourage or to prevent biofilm formation. Introducing bacteria into groundwater containing minerals may lead to differences in attachment of the bacteria onto different mineral surfaces depending on their interaction potentials. The attachment process is governed by at least two types of interaction across the aqueous phase. These are the van der Waals (vdW) and Electrical Double Layer (EDL) interactions. This thesis focuses on both theoretically and experimentally determining these interactions as part of the attachment process. In order to determine the acid-base interaction energy, hydrophobicity (as the acid-base interaction energy is determined by the calculation from the value obtained from contact angle and surface tension values) of surfaces and contact angle measurements have been made by the asymmetric drop shape analysis technique and the thermodynamic approach has been used to calculate the surface tensions of bacteria and mineral surfaces. To determine the electric double layer (EDL) interaction potential, zeta potentials were measured by an electrokinetic technique (ZetaPALs). The streaming potential technique was also used with a cylindrical cell to measure zeta potentials of the mineral grains and bacteria suspension in contact with an aqueous phase. It was found that geometrical factor, surface charge and hydrophobicity effects play important roles in bacterial adhesion and these can be modelled as XDLVO theory interaction energies. A numerical van der Waals interaction energy for capsule shaped bacteria to flat mineral plate model is developed from Hamaker's Microscopic Approach and examined by the MapleSoft 14 computer programme. The van der Waals interaction energy from the capsule model is compared to the interaction energies between spherical shell bacteria and mineral surfaces at the early stage of the adhesion process. This numerical solution shows that the effect of different shaped bacteria and mineral surfaces on the interaction potential cannot be neglected even at small separation distances. Total interaction energy prediction using XDLVO found significant effects of environmental conditions including pH, ionic strength and mineral size and shape. The XDLVO model was found to most closely mirror the experimental results, which obtained from flow-cell attachment experiment under laminar flows where the bacterial adhesion was found well attached at pH between 5 to 6 in 0.1 M ionic strength.

Rhodococcus has been used in bioremediation because of its low eco- toxicity, high tolerance to harsh environments, and ability to be cultivated in mixed microbial consortia with certain contaminants as its nutrients. Excretion of extracellular polymeric substances (EPS) allows Rhodococcus to trap and to effectively degrade contaminants. Mycolic acid (MA) which covers the cell wall provides Rhodococcus with a hydrophobic cell surface to contact hydrocarbon contaminant droplets. This work concerns the influence of the conformational change in MA and rhodococcal EPS on their mechanical properties. Neutron reflection revealed that when the solution pH increases, a hydration layer is generated between the bound (hydrophobic) MA (LB _MA) and the silicon substrate, whereas the intermolecular repulsion unfolds the extractable (hydrophilic) MA (LS_MA), and allows water to fill in the formerly folded space. Force spectroscopy using a polystyrene colloidal probe showed that the strength of the adhesion force between a hydrophobic particle and MA is affected by the conformation of MA. The existence of a hydration layer in the MA enhances cell adhesion. Classical DLVO theory indicated that the electrostatic force dominates the long range (a distance larger than the Debye length) interactions between a polystyrene (hydrophobic) particle and MA, whereas the van der Waals force has a negligible influence. EPS generated at the early exponential phase (E EPS) and the late stationary phase (S EPS) of Rhodococcus manifested different physiochemical and mechanical properties. Force spectroscopy using Rhodococcus as a bacterial cell probe suggested that S EPS possess a higher differential capacitance than E EPS do for cells to store charges and energy. The nonspecific binding sites to silicon (an abundant material in the sediments of groundwater) are not evenly distributed; they exist mainly in S EPS close to the cell surface, but rarely in E EPS. Therefore, S EPS have a stronger adhesion to the silicon surface than E EPS do. Contraction and stretch of the EPS chains affect the strength of the adhesion force to a silicon surface. S EPS possess a better resilience against compression than E EPS do, thus retaining water in both S EPS and the inner E EPS. 4