Bacteriology Lecture 10- Environmental Microbiology

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Bacteriology Lecture 10- Environmental
Microbiology
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Flow of energy in ecosystems
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Carbon cycle
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Nitrogen cycle
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Examples of nitrogen fixers
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Treatment of waste products by Nitrogen-fixers
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Sulphur cycle
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Metabolism is the sum of catabolism and anabolism
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Carbon and Energy
Carbon makes up half the dry weight of bacterial
cells.Important for living things because 4
valences allow formation of large complex
molecules. Obtained from organic molecules by
heterotrophs, and from carbon dioxide by
autotrophs.
Energy obtained from sunlight by phototrophs
and from inorganic or organic compounds by
chemotrophs.
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The main types of energy-capturing metabolsim
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Photoautotrophs, Energy from Light Carbon from CO2

• Transform CO2 and reducing agent into
  carbohydrates and O2 by photosynthesis i.e.
  conversion of light energy into chemical energy
  by trapping of light in chlorophyll.
• Cyanobacteria (and plants) use chlorophyll a for
  the photsynthetic reaction
• 6CO2 12H2O C6H12O6 6O2 6H2O

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Green sulphur and purple sulphur bacteria use
sulphur, sulphur compounds or hydrogen gas to
reduce carbon dioxide and form organic compounds.
They have a different type of chlorophyll called
bacteriochlorophyll which absorbs light of a
longer wavelength. Examples of green sulphur
bacteria are Chlorobium spp and purple sulphur
are Chromatium spp.
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Photoheterotrophs, Energy from Light, Carbon from
Organic Compounds

• e.g. green nonsulphur (Chloroflexus) and purple
  nonsulphur bacteria (Rhodopsuedomonas).
• Sources of carbon include alcohols, fatty acids,
  organic acids and carbohydrates.

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Formation of zones in a typical lake or pond
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Chemoautotrophs (Chemolithotrophs),Energy from
Inorganic Compounds, Carbon from CO2

• Energy source examples hydrogen sulphide,
  sulphur, ammonia, nitrites, hydrogen gas, Fe2.
• e.g. two genera important in nitrogen cycle
  Thiobacillus also important in sulphur cycle
• Thiobacillus spp.
• 2S 3O2 2H2O 2H2SO4
• Nitrobacter spp.
• 2NaNO2 O2 2NaNO3

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Chemoheterotrophs, Energy and Carbon from Organic
Compounds

• Usually use the same organic compound for both
  carbon and energy.
• The vast majority of bacteria (including almost
  all species of medical or industrial importance),
  all fungi, protozoans and animals are
  chemoheterotrophs.

• Heterotrophs further classified according to
  source of organic molecules
• saprophytes live on dead organic material
• parasites feed on a living host.

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Relative proportions of organisms found in soil
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Overview of sewage treatment process
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Trickling filters
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Testing water purity- multiple-tube fermentation
method
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Testing water purity- membrane filter test
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Industrial Microbiology
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Industrial Bacteriology
Food Production Organic Compounds Antibiotics Enzy
mes Amino Acids Other Biological
Products Recombinant DNA Technology Microbiologica
l Mining Microbiological Waste Disposal
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Bacteria as Food Source

• Known as single-cell protein being investigated
  as solution to world food problem.
• Bacteria being investigated because a huge
  variety of substances including industrial waste
  products can be used by bacteria as substrate for
  biomass production.

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• Examples of bacteria used as food
• Cyanobacteria, Spirulina grown in alkaline lakes
  in Africa, Mexico and by Incas in Peru.
  Dried-made into cakes!
• Pruteen, Methylophilus methylotrophus grown on
  methanol, and proposed as animal feed. 70
  protein. Problems with commercial viability due
  to subsidisation of alternative animal feeds.

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Bacteria in Food Production Dairy Products

• Rely on production of lactic acid or alcohol as
  well as other variable by-products of
  fermentation e.g.
• Streptococcus and Leuconostoc spp. used to make
  buttermilk and sour cream with different flavors
  by adding bacteria to pasteurised skim milk or
  cream respectively.
• Yoghurt made by adding Streptococcus thermophilus
  and Lactobacillus bulgaricus to milk.

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Cheese made by adding lactic acid bacteria and
either rennin or bacterial enzymes to milk. The
bacteria sour the milk and the enzymes coagulate
the milk protein casein. The liquid whey is
removed to varying degrees, depending on the
hardness of the cheese, and the solid curd is
usually ripened by a mixture of bacteria. These
produce lactic and other acids, alcohols,
proteolytic enzymes and lipases, which flavour
and soften the cheese
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Bacteria in Food Production Other Fermentations

• Vinegar made e.g. by fermenting apple juice or
  grape juice to produce ethanol. Then,
  Acetobacter aceti oxidise ethanol to acetic acid.
• Sauerkraut packed shredded cabbage in 2-3 salt
  fermented by anaerobic halophilic species of
  Lactobacillus and Leuconostoc. Bacteria produce
  lactic acid, acetic acid, carbon dioxide, alcohol
  and other substances.

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• Pickles cucumbers in brine fermented by
  Leuconostoc or Pediococcus spp. Later add
  vinegar, spices and sometimes sugar, and usually
  pasteurise.
• Olives Leuconostoc and Lactobacillus

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Bacteria in spices
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Organic Solvent Production

• Microbes can produce hundreds of different
  chemicals, but many manufactured more
  economically by chemical synthesis. This may
  change as oil prices rise, especially if the
  microbes are genetically engineered to increase
  output.
• Microbes used in part of production of ethanol,
  acetone and butanol e.g. thermophilic clostridia
  and Zymomonas being used in alcohol production.
• Clostridium acetobutylicum produces butanol and
  acetone when grown on starch. (Butanol used in
  making brake fluid, resins and petrol additives
  acetone used as solvent).

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Production of Organic Acids

• Acetic acid made by several species e.g.
  thermophiles can make it from cellulose and
  others can make it from hydrogen and carbon
  dioxide. Used in manufacture of rubber,
  plastics, fabrics, insecticides, photographic
  materials, dyes and pharmaceuticals. Also made by
  Acetobacter from ethanol in food industry.
• Lactic acid made by Lactobacillus delbrueckii
  from glucose and used in foods, textiles,
  plastics and electroplating.

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Production of Antibiotics

• About 100 antibiotics manufactured in large
  quantities since first production of penicillin
  in 1940s. Improve yields by using mutated
  strains and improving fermentation
• procedures e.g. strain that once produced 60 mg
  of penicillin per litre of culture now makes 20
  g/l.
• Many antibiotics now are semi-synthetic i.e. made
  partly by microbes and modified by chemists.
• Made by fungi and bacteria (esp. Streptomyces
  spp.)

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Amino Acid Supplements
Of the 20 amino acids in proteins, 8 cannot be
synthesised by most animals and must therefore be
obtained in the diet (i.e. essential amino
acids). Lysine and methionine are present in
only small amounts in grains, and are therefore
added to animal feed, and sold as supplements for
human consumption. Methionine made synthetically
but.
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• Lysine made by an overproducing mutant strain of
  Corynebacterium glutamicum which lacks feedback
  inhibition.
• Glutamic acid used as food flavouring -
  monosodium glutamate. Made by C. glutamicum
  mutant which makes high yields of glutamic acid
  (as offshoot of TCA cycle) and which can excrete
  the amino acid from the cell when grown in media
  which results in a leaky cytoplasmic membrane.

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Other Products

• Polysaccharides e.g.
• xantham gum produced from Xanthomonas campestris
  and used in foods for its pseudoplasticity
  property
• dextran made by Leuconostoc spp.used in medicine.
• Vitamins e.g.
• vitamin B12 and
• riboflavin

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Bacteria in Agriculture

• Pest Control
• Bacillus thuringiensis Photorhabdus and
  Xenorhabdus spp. and their nematode symbionts
  used to kill insect pests. Organism may be
  applied directly or insecticidal toxin gene may
  be engineered into the plant.

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Recombiniant DNA Technology

• Human genes cloned into E. coli and yeast to
  produce insulin, growth hormone, interferons.
• Vaccines made by cloning genes coding for
  antigenic surface proteins from pathogens into E.
  coli and yeast.

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Plants can be genetically engineered with useful
genes placed on the Ti plasmid of Agrobacterium
tumefaciens, which integrates part of its DNA
into the chromosome of infected plants. The
plasmid is engineered so that it can no longer
cause the crown gall disease tumors. Genes
engineered into plants include those for
herbicide resistance, pest resistance, shelf life
etc.
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• Pseudomonas syringae -ice-minus bacteria -
  recombinant strains cant make proteins which act
  as nuclei for ice crystal formation. Use to
  colonise surface of plants to replace normal
  bacterial flora. Allows plants to survive brief
  freezing at -3oC.

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Microbial Mining

• Microbes can be used to extract minerals from
  less concentrated ores.
• Copper, zinc, iron, lead and uranium found as
  sulphide minerals.
• Thiobacillus ferrooxidans is a chemoautotroph
  which oxidises the sulphur in copper or iron
  sulphide with a resultant release of pure copper
  or iron. This process is even more rapid in
  presence of T. thiooxidans as well.

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• Bioremediation - the use of microbes to detoxify
  chemical wastes. Examples
• Arochlor 1260 is one of the most toxic of the
  polychlorinated biphenyl compounds, and three
  strains of microbes have been found which
  deactivate it.
• Other organisms have been found to detoxify
  cyanide and dioxin and to degrade oil spills. A
  genetically modified bacterium can degrade Agent
  Orange.
• Research ongoing on microorganisms found in waste
  dumps, but little genetic characterisation as
  yet, so genetic modification limited so far.