Transcript Bacteria - leavingcertbiology.net

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
Basic Structure of Bacterium
Cell membrane
Cytoplasm
Flagellum
Capsule
Cell Wall
Plasmid
DNA
(nucleoid)
(Note: rod-shaped bacterium)
Types of Bacterium
1. Rods
2. Round
3. Spirals
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
Binary Fission
DNA and plasmid
replicated
Bacterial
cell splits in
two
Bacterium elongates
and DNA and
plasmid move to
opposite ends of cell
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
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
Parasitic Bacteria
• Parasitic bacteria are usually diseasecausing (pathogenic) bacteria:
– Helicobacter pylori:
• Stomach ulcers
– Clostridium botulinum:
• Botulism
– Streptococcus pneumoniae:
• Pneumonia
• Bacterial meningitis
– Treponema pallidum:
• Syphilis
– Streptococcus pyogenes:
• Strep throat
• Tonsilitis
• Scarlet fever
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)
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
Endospore Formation
Favourable
conditions
Endospore is
released
following
bacterial death
Unfavourable
conditions: DNA
and plasmid
replicated
Endospore is
formed around
replicated DNA
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
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)
Bacterial Growth Curve
Numbers of bacteria
STATIONARY
LOG
DEATH
SURVIVAL
LAG
Time (days)
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
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:
1. Batch Culture
2. Continuous Flow Culture
1. Batch Culture
i.
In batch culture, a fixed amount of food (batch of food)
is added to bioreactor
ii. 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
iii. Most of the product is formed in the log and stationary
phases (therefore reaction is normally stopped before
the death phase)
iv. At the end of the reaction the product is removed and
the bioreactor is cleaned out ready for another ‘run’
v. 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 don’t build up to high levels
2. Continuous Flow Culture
i.
ii.
iii.
iv.
v.
Nutrients are continuously infused into the
bioreactor of continuous flow cultures and
media removed is removed with product
In this way the bacteria are kept in the log
phase of growth
pH, temperature, oxygen concentration,
nutrient concentration and waste build-up are
tightly controlled to maintain optimal conditions
Advantage of continuous flow culture is that
product is continually produced
Disadvantage of continuous flow culture is that
conditions have to maintained within narrow
limits and this is very difficult and expensive