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Bacteriology Lecture 10- Environmental Microbiology


Bacteriology Lecture 10- Environmental Microbiology Of the 20 amino acids in proteins, 8 cannot be synthesised by most animals and must therefore be obtained in the ... – PowerPoint PPT presentation

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Title: Bacteriology Lecture 10- Environmental Microbiology

Bacteriology Lecture 10- Environmental
Flow of energy in ecosystems
Carbon cycle
Nitrogen cycle
Examples of nitrogen fixers
Treatment of waste products by Nitrogen-fixers
Sulphur cycle
Metabolism is the sum of catabolism and anabolism
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
Energy obtained from sunlight by phototrophs
and from inorganic or organic compounds by
The main types of energy-capturing metabolsim
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

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.
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.

Formation of zones in a typical lake or pond
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

Chemoheterotrophs, Energy and Carbon from Organic
  • 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
  • Heterotrophs further classified according to
    source of organic molecules
  • saprophytes live on dead organic material
  • parasites feed on a living host.

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

  • 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.

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.

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
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.

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

Bacteria in spices
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
  • 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).

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.

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
  • Many antibiotics now are semi-synthetic i.e. made
    partly by microbes and modified by chemists.
  • Made by fungi and bacteria (esp. Streptomyces

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
  • Lysine made by an overproducing mutant strain of
    Corynebacterium glutamicum which lacks feedback
  • 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.

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

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.

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.

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
  • 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.

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.

  • 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
  • Research ongoing on microorganisms found in waste
    dumps, but little genetic characterisation as
    yet, so genetic modification limited so far.
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