Chapter 20: Kingdom Monera

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Chapter 20 Kingdom Monera

• Bacteria are ubiquitous they are found
  everywhere
• Fresh water, sea water, air-borne, and soil
  bacteria
• Bacteria are prokaryotic in nature i.e. they
  have no membrane-bound nucleus or organelles
  the area occupied by the DNA in bacteria is
  called the nucleoid

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Basic Structure of Bacterium
Cell membrane
Cytoplasm
Flagellum
Capsule
DNA (nucleoid)
Cell Wall
Plasmid
(Note rod-shaped bacterium)
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Types of Bacterium

1. Rods
2. Round
3. Spirals

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Bacterial Reproduction

• Bacteria reproduce by a process called binary
  fission it is a type of asexual reproduction
• Bacterium replicates its DNA and plasmid
• The two pieces of DNA and plasmids move to
  opposite ends of the cell
• The bacterium splits in two
• In ideal conditions bacteria are capable of
  reproducing every 20 minutes

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Binary Fission
DNA and plasmid replicated
Bacterium elongates and DNA and plasmid move to
opposite ends of cell
Bacterial cell splits in two
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Bacterial Nutrition

• Autotrophic (bacterium makes its own food)
• Photosynthetic bacteria contain chlorophyll and
  use sunlight energy to make food e.g. purple
  sulphur bacteria
• Chemosynthetic bacteria use ammonia, sulphur and
  iron compounds to make food e.g. nitrifying
  bacteria

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Bacterial Nutrition

• Heterotrophic (bacterium obtains food made by
  other organisms)
• Saprophytic bacteria take in food from dead
  organic matter e.g. decomposer bacteria in soil
• Parasitic bacteria take in food from a live host
  e.g. disease-causing (pathogenic) bacteria

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Parasitic Bacteria

• Parasitic bacteria are usually disease-causing
  (pathogenic) bacteria
• Helicobacter pylori
• Stomach ulcers
• Clostridium botulinum
• Botulism
• Streptococcus pneumoniae
• Pneumonia
• Bacterial meningitis
• Treponema pallidum
• Syphilis
• Streptococcus pyogenes
• Strep throat
• Tonsilitis
• Scarlet fever

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Factors Affecting Growth

1. Temperature (lower temperature slow down enzyme
   action and hence bacterial growth)
2. Oxygen (although some bacteria do not use oxygen)
3. pH (enzymes are affected by pH and thus pH
   affects bacterial growth and metabolism)
4. Solute concentration (osmosis affects bacterial
   metabolism)
5. Pressure (air pressure affects bacteria due to
   the cell wall not being strong enough to
   withstand high pressures)
6. Water (although some bacteria do not use water,
   others resort to endospore formation when there
   is not enough moisture)

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Endospore Formation

• Under unfavourable conditions bacteria are still
  able to survive they do this by forming
  endospores that protect the bacterial cells from
  harsh conditions
• Endospore formation
• The bacterial DNA is replicated and is then
  enclosed within a tough protein-carbohydrate coat
  complex
• When the bacterial cell dies the endospore is
  released and can survive a very long time
• The endospore absorb water when conditions become
  favourable again and the bacterium reproduces
  again by binary fission

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Endospore Formation
Unfavourable conditions DNA and plasmid
replicated
Favourable conditions
Endospore is released following bacterial death
Endospore is formed around replicated DNA
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Economic Importance of Bacteria

• Two beneficial effects of bacteria
• Lactobacillus is used to produce yoghurt and
  cheese
• Escherichia coli has been genetically modified
  (by introduction of human genes) to produce human
  insulin and growth factor as well as enzymes,
  certain amino acids, and vitamins
• Two harmful effects of bacteria
• Bacteria cause human disease (pathogenic)
• Bacteria cause food to spoil

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Antibiotics

• Antibiotics are chemicals produced by
  microorganisms that are able to prevent growth
  of, or kill, other microorganisms without
  damaging animal tissues
• Antibiotics are used to control bacterial
  infections in humans and animals
• Antibiotics have been overused by some, thereby
  increasing antibiotic resistance among certain
  strains of bacteria (there are a handful of
  bacterial strains that now have complete
  resistance to all known antibiotics and this
  could create a human pandemic in the future)

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Bacterial Growth Curve
STATIONARY
Numbers of bacteria
LOG
DEATH
SURVIVAL
LAG
Time (days)
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Bacterial Growth Curve

• There are 5 phases of bacterial growth
• Lag bacteria are adapting to environment no
  increase in bacterial numbers
• Log bacteria have ideal conditions and are
  reproducing at their maximal rate
• Stationary conditions become limiting such as
  food/space and bacterial reproduction bacterial
  death
• Decline/Death continued lack of food and space
  and build-up of toxins causes the death rate to
  increase above the reproduction rate and the
  numbers fall
• Survival a small number of bacteria survive as
  endospores and remain dormant until conditions
  become favourable again

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Bioprocessing

• As well as enzymes, bacteria can be used in
  bioprocessing to produce useful products
  including yoghurts, cheeses antibiotics, human
  proteins etc.
• There are two methods by which bacteria are used
  in bioprocessing
• Batch Culture
• Continuous Flow Culture

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1. Batch Culture

1. In batch culture, a fixed amount of food (batch
   of food) is added to bioreactor
2. The bacteria go through the lag, log and
   stationary phases of growth before the reaction
   is stopped and a certain amount of product is
   formed
3. Most of the product is formed in the log and
   stationary phases (therefore reaction is normally
   stopped before the death phase)
4. At the end of the reaction the product is removed
   and the bioreactor is cleaned out ready for
   another run
5. Advantages of batch culture are that it is easy
   to control, it can be run only when needed, and
   the bacteria go through a normal life cycle and
   so waste products dont build up to high levels

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2. Continuous Flow Culture

1. Nutrients are continuously infused into the
   bioreactor of continuous flow cultures and media
   removed is removed with product
2. In this way the bacteria are kept in the log
   phase of growth
3. pH, temperature, oxygen concentration, nutrient
   concentration and waste build-up are tightly
   controlled to maintain optimal conditions
4. Advantage of continuous flow culture is that
   product is continually produced
5. Disadvantage of continuous flow culture is that
   conditions have to maintained within narrow
   limits and this is very difficult and expensive