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  • 1. Mechanisms of Bacterial Resistance Against Mercury Toxicity
    By Monique Smit
    Supervisor: Prof Erick Strauss
    http://www.ramehart.com/newsletters/mercury_drops.jpg
  • 2. Introduction
    Why is Mercury so TOXIC?
    Mercury
    Mercury Poisoning
    Different Enzymatic Mechanisms of Mercury Detoxification
    General Mechanism
    Adaptationsof Different Bacteria
    Conclusions
  • 3. Mercury ‘Hydrargyrum’
    ‘hydr’: watery
    ‘argyros’: silver
    ‘Mad as a
    Hatter !’
    Roman god, Mercury
    http://www.ecorazzi.com/wp-content/uploads/2009/06/depp_madhatter.jpg
  • 4. Why is Mercury so TOXIC?
  • 5. Mercury: Properties
  • 6. Mercury: Occurrence
    Earth’s crust:
    Lower crust: 21 ppb
    Upper crust : 56 ppb
    Forms:
    Elemental
    Deposits; Cinnabar (HgS, Binary Minerals)
    Transformation available (three redox states)
    http://www.google.co.za/imgres?imgurl=http://www.kidsgeo.com/images/earths-crust.jpg&imgrefurl=http://www.kidsgeo.com/geology-for-kids/0021-earths-crust.php&usg=__dZYwJ_hngjFJrDMaXCWykpchXp8=&h=338&w=338&sz=29&hl=en&start=0&zoom=1&tbnid=ygnWpZE4hwsLnM:&tbnh=123&tbnw=121&prev=/images%3Fq%3DEarth%2Bcrust%26hl%3Den%26biw%3D1366%26bih%3D552%26gbv%3D2%26tbs%3Disch:1&itbs=1&iact=hc&vpx=117&vpy=92&dur=2547&hovh=225&hovw=225&tx=140&ty=84&ei=lKOUTNCpMcKblgeRpdGnCg&oei=lKOUTNCpMcKblgeRpdGnCg&esq=1&page=1&ndsp=24&ved=1t:429,r:0,s:0
  • 7. Mercury: General Uses
    Thermometers
    Barometers
    Manometers
    http://www.home-weather-stations-guide.com/images/Howardmiller-presqueisle-fromAmazon.jpg
    http://www.greenlight300.com/pictures/02_why_mercury.jpg
    http://themoderatevoice.com/wordpress-engine/files/2008-june/mercury_thermometer.jpg
    http://www.oncallmedicalsupplies.com/acatalog/0125large.jpg
  • 8. Mercury: Applications to Different Sectors
    Google Images
    Growing CONCERN?
  • 9. Mercury Poisoning
    Exposure : High toxicity: mercurialism
    Minamata Disease
    • Ataxia
    • 10. Impairment of speech & hearing
    Acrodynia(‘Pink Disease’)
    • Pain
    • 11. Pink discolouration
  • Different Methods to Exposure
    Ingestion Inhalation Skin Contact & Absorption
  • 12. Effects on Health
    • Nervous system deterioration
    • 13. Hearing, speech, vision impairment
    • 14. Involuntarymuscle movements
    • 15. Skin & mucous membrane corrosion
    Google Images
  • 16. Mercury Poisoning
    Exposures to differentforms
    Inorganic & Organic Mercury
  • 17. Mechanism of Action
    Hg binds to Sulfhydryl groups
    INCAPACITATION of key enzymes
    Severely DamagedNervous System
    NO:
    - Involvement in Cellular Stress Response
    - Protein Repair
    - Oxidative Damage Prevention
  • 18. Different Enzymatic
    Methods Of Mercury Detoxification
  • 19. Bacteria to the rescue?
    DEFENCE Mechanisms  Reductionof Hg
    Natural& Engineered role in bioremediation???
    http://ianjuby.org/newsletters/superbacteria.jpg
  • 20. General Mechanism
    CommonMechanism
    ‘mer’ Operon, respective Mer proteins
    Mercury Resistance Genes:
    *Gram NEG. bacteria
  • 21. Mercury Resistance Genes
  • 22. General Mechanism
    Detoxification Process:
    Transport of Hg(II) into the cell
    Delivery of Hg(II) to Reductase
    Reduction
    Export of reduced Hg(II)
    1
    2
    3
    4
  • 23. 1
    CELL MEMBRANE
    4
    CYTOPLASM
    2
    3
    N.L Brown et al. (2002)
  • 24. Adaptationsof Different Bacteria
    Diversity of Hg Resistance Loci
    Variationin mer operon
    structure
    Mer as part of mobile
    genetic elements
  • 25. Diversity of Hg Resistance Loci
    Variationin operon structure
    Difference between Gram+ and Gram- Bacteria:
    An additional enzyme, MerB
    seldom found in Gram- bacteria
    but dominantlyfound in Gram+
    bacteria
  • 26. Diversity of Hg Resistance Loci
    Mer operon as part of mobile
    genetic elements
    Mer resistance operon  transposons
    Transposons carry integronswith
    1/more antibiotic resistance genes
    HOW?
    Horizontal Gene Transfer & Recombination
    Events
  • 27. Bacteria used in bioremediation?