A 17.1 Kb genetic element encoding for mercury resistance (OCT-Hg^r) was shown to translocate from its original location on the OCT plasmid to the resistance plasmid, RPl, in Pseudomonas putida. Analysis of RPl-Hg^r recombinant plasmids revealed that insertion of mercury resistance genes into RPl could occur at a variety of sites, with all recombinants having common EcoRI restriction fragments of 9.4, 3.8, 2.3, and 1.6 Kb, derived from the insertion. Hybridization analysis suggested the existence of extensive homology between this insertion and the prototypic mercury resistance transposon, Tn501, as well as the location of a similar merA sequence. Although the overall size was shown to be quite different from Tn501, striking physical similarities are shared between these two elements.

Translocation of a 17.1 kilobase region of the OCT plasmid encoding mercury resistance (mer) in Pseudomonas putida was shown to occur in a recombination-deficient host with plasmid PP1 serving as a recipient replicon. The frequency of transposition in Pseudomonas was estimated at 10^3 -10 -^2, but undetectable in Escherichia soli. ' DNA comprising all of mr as well as subregions there of were cloned and subjected to DNA sequence analysis. Like other transposons, mer was found to contain inverted repeat sequences at its termini. These were similar to, but not identical to the inverted repeat structures found in the prototypical mercury resistance transposon Tn501 from E. aeruginosa.

At diploma thesis will be used for determination of alkyl - derivatives of mercury especially gass chromatography. At diploma thesis will be developed metod for it´s identification, quantification, standard operating procedure and validation of the method of determination of alkyl - derivatives of mercury in animal tissues. There will be evaluated level of contamination by the polutants.

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Mercury poses significant challenges to human health and fisheries management. Historical industrial practices in Waynesboro, Virginia left portions of the Shenandoah River basin contaminated with mercury and stringent health advisories for fish consumption. I investigated processes affecting the bioaccumulation of mercury in Catostomus commersoni, Ictalurus punctatus, Lepomis auritus, and Micropterus dolomieu by studying food habits, total mercury and methylmercury in common prey items, and bioaccumulation dynamics of methylmercury in the mercury contaminated South River and South Fork of the Shenandoah River and uncontaminated North River. Additionally, I evaluated sexual and seasonal variations of total mercury in M. dolomieu in the South Fork of the Shenandoah River. Algae, aquatic insects, crayfish, detritus, and fish accounted for 75-97% of the diet. Total mercury in aquatic invertebrates and forage fish in contaminated rivers ranged from 66.7-398.3 and 198.0-594.9 ng/g wet weight, while total mercury in aquatic invertebrates and forage fish in the reference river were 4.4 and 29.3 ng/g. Model simulations indicated that dietary pathways accounted for 87% of methylmercury uptake by fish in contaminated rivers, but only 57% in the reference river. Total mercury in M. dolomieu was 19-20% higher in females than males and 14-21% higher during spring than summer and fall. Results of this study indicate that bioenergetics-based bioaccumulation models are valuable tools for evaluating field data, identifying processes critical to contaminant accumulation, and comparing outcomes of alternative management options associated with pollution control, ecosystem management, and/or restoration activities for management guidance prior to costly expenditures. / Master of Science

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Aquatic organisms experience intermittent exposure to contaminants. The hazard from such discontinuous exposure may not simply be predicted from existing continuous exposure. Little is known about the bioaccumulation responses of shellfish to metals during intermittent compared to the continuous exposure counterparts. This study was designed to compare the bioaccumulation responses of two metals (Cd and Hg) singly (Chapters 3 and 4) or mixtures (Chapters 5 and 6) during continuous and intermittent exposure. Responses were examined using a multi-assay approach in areas of oxidative stress, osmoregulation, haematology and organ pathology. Tissue metal concentrations were highest in the gill and digestive gland for both metals. The linear or curvilinear pattern of accumulation was observed in the continuous exposure. While an alternating temporal uptake and clearance corresponding with the exposure was observed in the gill (Hg alone) and haemolymph (Cd alone) in intermittent profile. At the end, the study shows that accumulation of Hg or Cd was less in the intermittent compared to the continuous exposure for most tissue. Sub-lethal responses during Hg or Cd alone were similar in both regime apart from the severe pathology in the gill (continuous exposure) and inflammation in the digestive gland (intermittent exposure) observed in the Hg alone treatment (Chapter 4). For Hg plus Cd mixture, the additive effect in accumulation was observed in both exposures. Sub-lethal responses during mixtures were not affected in the intermittent. However, an antagonistic interaction was observed in the TBARS during continuous exposures for all tissues apart from the digestive gland. In terms of risk assessment, regulations for the single metals in continuous exposure will be protective for intermittent events at least for adult M.galloprovincialis.