Anaerobic Microbiology and Biofilms

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• Anaerobic Microbiology and Biofilms

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Anaerobic Microorganisms

• Anoxic environments are common
• Sediments of lakes, rivers, oceans
• Bogs and marshes
• Waterlogged soil
• Canned foods
• GI tract of animals
• Oral cavity esp around teeth
• Sewage treatment systems
• Deep underground areas

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What Microrganisms are Anaerobes?

• Obligate anaerobiosis occurs in 3 groups of mos
  wide variety of prokaryotes, a few fungi, a few
  protozoa
• Well known obligate anaerobic bacterium is
  Clostridium Gram spore forming rod
• Other obligate anaerobes are found in
• Methanogens and other archae
• Sulfate reducing bacteria
• Sensitivity to O2 varies

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O2 As a Factor in Microbial Growth

• Aerobes capable of growth at full oxygen
  tension (21) some hyperbaric
• Microaerophiles can use O2 only when present at
  levels lower than found in air
• Facultative grow either in presence or in
  absence of O2
• Anaerobes lack respiratory system 2
  kinds aerotolerant anaerobes
• obligate anaerobes

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Anaerobes

• Aerotolerant anaerobes
• Tolerate and grow in presence of O2
• Cant use it
• Obligate anaerobes
• Killed by O2
• Lack enzymes that decompose toxic oxygen
  compounds
• Many anaerobes also contain flavin enzymes which
  can react with O2 to produce toxic O2 products

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Toxic Forms of Oxygen

• Oxygen is a powerful oxidant and a good electron
  acceptor for respiration
• Normal form called triplet oxygen
• Toxic forms include
• Singlet oxygen
• Superoxide anion (O2-)
• Hydrogen peroxide (H2O2)
• Hydroxyl radical (OH-)

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Superoxide Anion, Hydrogen Peroxide Hydroxyl
Radical

• All produced as byproducts during reduction of O2
  to H2O during respiration
• O2 e- ? O2- Superoxide
• O2- e- ? H2O2 Hydrogen peroxide
• H2O2 e- ? H2O OH. Hydroxyl radical
• OH. e- ? H2O Water
• Flavoproteins, quinones, thiols, and iron
  sulfur proteins can also do Rxn 1

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i) Singlet Oxygen

• A major toxic form is singlet oxygen
• A higher E form in which outer shell electrons
  become vv reactive and carry out undesired
  oxidations
• Produced photo and biochemically (peroxidase
  enzymes)
• Carotenoids convert this to nontoxic forms

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ii) Superoxide Anion

• Highly reactive
• Can oxidise most organic compounds in cell
• Destroyed by the enzyme superoxide dismutase
• O2- O2- 2H ? H2O2 O2

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iii) Hydrogen Peroxide

• Peroxides damage cell components but not as
  toxic as superoxide and hydroxyl radicals
• Catalase and peroxidase destroy H2O2
• H2O2 H2O2 ? 2H2O O2 (catalase)
• H2O2 NADH H ? 2H2O NAD
  
  (peroxidase)

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Combined SOD/ Catalase Reaction

• 4 O2- 4H ?? 2 H20 302
• i.e. bring about conversion of superoxide to
  oxygen

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iv) Hydroxyl Radical

• Most reactive of all species
• Instantly oxidises any organic molecule
• Luckily it is only a transient species in cells
  as it is mainly produced by ionizing radiation
• Small amt prod from H2O2, but this doesnt
  accumulate due to catalase

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• Biofilms

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Definition

• Colonies of microbial cells encased in slime and
  attached to a surface

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Simple and Complex Biofilms

• Simple biofilm develops when mos attach and form
  a monolayer of cells
• Depending on environment, biofilms can become
  more complex with layers of different organisms
• Eg PS organisms at surface
• facultative chemoorganotrophs in middle
• Sulfate reducers at bottom

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Mature Biofilms

• With time, find structures of cell aggregates,
  interstitial pores and conduit channels
• Cell aggregates develop by growth of attached
  mos (thus more cells added to surface of
  aggregate) and by trapping of free floating mos
• Channels shaped by protozoa which graze on
  bacteria

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What Surfaces can be Exploited?

• Both inert and living organism surfaces
• Rocks in stream
• Dirty food bowl
• Contact lens
• Teeth and gum area
• Skin
• Tongue
• Catheter devices

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Biofilms on Living Organisms

• These microorganisms benefit because the surfaces
  release nutrients (old skin cells, soluble
  material, gases)
• Play a major role in disease
• Protect pathogens from disinfectants
• Create focal point for later occurrence of
  disease
• Release mos or microbial products that affect
  immunological system of host
• NB in occular devices eg contact lenses and
  cleaning solution