Download Bacteria reproduce asexually The method used by a bacteria

Chpt. 21
Monera
Monera
• Bacteria belong to the kingdom monera.
• Bacteria are present in a wide range of habitats
including both land and water environments e.g. salt
water, soil, plants, animals etc.
• Bacteria also survive in extreme environments e.g. hot
springs, swamps, human intestines, human stomach
(pH 2) etc.
• Bacteria are prokaryotes i.e. no nucleus or membrane
enclosed organelles – mitochondria.
• Bacteria are unicellular – single celled.
• Bacteria contain DNA plasmids.
Bacterial Size
Bacterial Structure
Bacterial Structure
Ribosome
Cell wall
Food
Reserve
Cell membrane
Flagella
Cytoplasm
Capsule
Plasmid
DNA (Chromosome)
General Structure of Bacterium
Cell Wall: - made of sugars and protein
- prevents bacteria from swelling with water
and bursting
Cell Membrane: often has infoldings called mesosomes
which:
a) carry out respiration
b) help during cell division
Capsule: - sometimes present
- takes form of a semi-solid capsule or a more
liquid slime layer.
General Structure of a Bacterium
Chromosome: - one chromosome
- consists of a strand of DNA
- no surrounding membrane
- does not contain protein
Plasmids: - sometimes present
- small DNA loops
- contain genes that are responsible for
bacterial resistance to antibiotics
Cytoplasm: - contain ribosome's and numerous storage
granules (food or waste)
Flagellum: - sometimes present
- flagella allows bacteria to move by
themselves i.e. they are motile.
General Structure for a Bacterium
Bacterial Types
Bacteria are classified according to three shapes:
• Spherical (Cocci)
• Rod (Bacillus)
• Spiral (Spirrillum)
Bacterial Types
Bacterial Types
Spherical (Cocci):
- Round bacteria which can be found in pairs, chains or
clusters.
- E.g. Staphoolococcus aureus
causes pneumonia
Bacterial Types
Rods (Bacillus):
- E.g. Bacillus anthracis
Cause of anthrax
- Escherichia coli (E.coli)
Live in human gut
Bacterial Types
Spiral (Spirillum):
- E.g. Treponema pallidum
Causes syphilis
- E.g. Cholera
Reproduction in Bacteria
• Bacteria reproduce asexually
• The method used by a bacteria to reproduce is called
Binary Fission.
Binary Fission
• The chromosome attaches to the plasma membrane
and the DNA is replicated.
Cell wall
Cytoplasm
Plasma membrane
Chromosome
Binary Fission
• The cell elongates and the two chromosomes separate
Binary Fission
• The cell wall grows to divide the cell in two
Binary Fission
• Two identical daughter cells are formed
Binary Fission
Mutations in Bacteria
• Bacteria reproduce asexually - their offspring are
genetically identical.
• As there is little recombination of genetic material in
this method of reproduction one would expect that
bacteria would be slow to evolve.
• New mutations can spread very quickly within rapidly
growing bacteria allowing them to evolve very fast.
• This is how bacteria evolve resistance to new
antibiotics.
Endospores
• Some bacteria can withstand unfavourable conditions
by producing endospores.
Endospore Formation
• These are formed when the bacterial chromosome
replicates.
Endospore Formation
• One of the new strands becomes enclosed in a toughwalled capsule called an endospore.
Endospore
• The parent cell then breaks down and the
endospore remains dormant.
Endospore Formation
• When conditions are favourable the spores absorb
water, break their walls and reproduce by binary
fission.
• Note: endospores are very difficult to kill – can
withstand lack of food and water, high temperatures
and most poisons.
Bacterial Nutrition
• Bacteria obtain food in four different ways which can
be grouped under two headings:
Autotrophic
Photosynthetic
Chemosynthetic
Heterotrophic
Saprophytes
Parasites
Autotrophic Organisms: are organisms
which can make their own food.
Photosynthetic bacteria:
• Source of energy = light
• Chlorophyll on membranes within the cell.
• Some bacteria have different pigments than plants –
use mostly red light.
• Some bacteria live on hydrogen sulphide gas instead of
water – purple sulphur bacteria.
Autotrophic Bacteria
Chemosynthetic Bacteria:
• make their own food using energy from reactions
involving ammonia, sulphur and iron compounds.
• E.g. Nitrifying bacteria that convert ammonia
to nitrates in the nitrogen cycle
Heterotrophic Organisms: organisms which
take in food made by other organisms.
Saprophytes:
• take in food from dead organic matter e.g. bacteria of
decay in the soil.
• some use petrol and oil products as a food source –
clean up oil spills.
Heterotrophic Bacteria
Parasites:
• take in food from a live host resulting in damage to
host.
• Examples of disease causing bacteria include:
cholera
pneumonia
Heterotrophic
(Take in food)
Saprophytic
e.g.
bacteria
of decay
Parasitic
e.g.
Streptococci
Autotrophic
(make food)
Photosynthetic
e.g.
Purple
sulphur
bacteria
Chemosynthetic
e.g.
Nitrifying
bacteria
Factors Affecting Growth
Growth of bacteria is affected by five factors.
Too much or too little of any of these five factors will
slow down the growth of bacteria:
• Temperature
• Oxygen concentration
• pH
• External solute concentration
• Pressure
Temperature
• Most bacteria grow well between 20°C and 30°C.
• Some can tolerate much higher temperatures
without their enzymes becoming denatured.
• Low temperatures slow down the rate of bacterial
growth.
• High temperature bacteria used in biotechnology
resulting in a) faster bacterial metabolism
b) higher rate of product formation
Oxygen Concentration
• Aerobic bacteria: require oxygen for respiration e.g.
Streptococcus.
• Anaerobic bacteria: do not require oxygen to respire
e.g. Clostridium.
• Facultative anaerobes: can respire with or
without oxygen e.g. E.Coli (found in intestines)
• Obligate anaerobes: can only respire in the
absence of oxygen e.g. Clostridium tetani
(causes tetanus)
pH
• Bacterial enzymes work at specific pH values, outside
this pH value they become denatured.
• For most bacteria the most suitable pH is pH7.
• Some bacteria can survive at very low or high pH
values.
External Solute
Bacteria can gain or loose water by a process called
osmosis.
Case 1: If environment outside a bacterial cell has a
higher solute concentration than the bacterial
cytoplasm, water will move out of the bacteria
(osmosis). As a result bacterium becomes dehydrated
preventing further growth or reproduction.
Case 2: If environment outside a bacterial cell has a
lower solute concentration than the bacterial
cytoplasm, water will enter the bacteria (osmosis).
- cell wall prevents bacterium from bursting
- most bacteria live in these conditions.
Pressure
• High pressure damages bacterial cell walls.
• Some bacteria can withstand very high pressures –
bacteria in deep-sea vents.
• Genetically modified bacteria are used to allow
bacteria to survive in bioreactors that require high
pressure.
Economic Importance of Bacteria
( Must know 2 beneficial and 2 disadvantages of bacteria)
Beneficial Bacteria:
1. Bacteria such as Lactobacillus are used to convert
milk to products such as cheese and yoghurt
2. Genetically modified bacteria e.g. E. Coli are used to
make products such as insulin, enzymes, drugs, food
flavourings and vitamins
Economic Importance of Bacteria
Harmful Bacteria:
1. Micro-organisms that cause disease are called
pathogens.
E.g. Bacillus anthracis causes anthrax in humans
- If they enter the body through a wound they can
multiply and effect the nerves and activity of
muscles.
- Other bacterial diseases include tuberculosis,
typhoid, cholera, diphtheria and brucellosis.
2. Bacteria cause food decay:
E.g. Lactobacilli cause milk to turn sour
Beneficial and harmful bacteria
BENEFICIAL
HARMFUL
• Lactobacillus converts milk •
to yoghurt and cheese
• Antibiotics can be formed by
some microorganisms
•
• Bacteria in the colon help
produce vitamins
• G.M.O.’s are used to make
•
insulin and other useful
compounds
•
• Bacteria are active in the
Carbon and Nitrogen Cycles
Pathogenic Bacteria can
cause diseases in humans
and animals.
Pathogenic Bacteria can
cause diseases in plants.
Bacteria can cause food
spoilage
Bacteria can cause tooth
decay.
Antibiotics
Antibiotics are
substances produced
by micro-organisms
that stop the growth
of, or kill, other
micro-organisms
without damaging
human tissue
Antibiotics
Antibiotics can be used to
control bacterial and fungal
infections but do not effect
viruses
E.g. Penicillin, streptomycin
Antibiotics
• The first antibiotic, Penicillin, was isolated from a
fungus by Sir Alexander Fleming.
• Now antibiotics are mostly produced by genetically
engineered bacteria.
Antibiotic Resistance
• When an antibiotic is used to treat an infection most of
the bacteria are killed.
• However mutations in bacterial genes can allow
bacteria to develop antibiotic resistance.
• Antibiotics will then kill ‘sensitive’ bacteria and favour
resistant bacteria.
• Bacterial strains have emerged which are resistant to
almost all known antibiotics (multi-resistant). As a
result present day antibiotics become ineffective. MRSA
is one example.
Potential Abuse of Antibiotics
Overuse of antibiotics:
• This results in the increased growth of antibiotic
resistant bacteria.
• Failure of some patients to complete a course of
antibiotics prescribed to them by a doctor allows the
bacteria to survive and re-grow.
Growth Curves of Monera
Higher Level
Binary Fission in monera can occur every 20 minutes
resulting in a very fast increase in bacterial numbers.
Because of this we use a special scale called the
logarithmic scale to represent these large numbers.
In a logarithmic scale each division represents a unit
increase in the value of x in the term 10x.
100 = 0
101 = 10
102 = 100
103 = 1000
104 = 10,000
105 = 100,000 etc
Growth Curve for Bacteria
This scale allows huge numbers of bacteria to be
represented on a graph as shown below:
Lag phase
Log Phase
Stationary Decline Phase
Number of Bacteria
Logarithmic Scale
Phase
Time
The Lag Phase:
• During this phase the bacteria are adapting
themselves to their new environment.
•Bacteria are producing the enzymes necessary to
digest the nutrients on which they are to grow.
•The rate of growth begins to increase towards the end
of this phase.
The Log (Exponential) Phase:
• There is a rapid period of growth during this phase
due to the fact that:
 The rate of cell division is currently at its maximum
with the number of bacteria doubling as often as
every 20 minutes.
 Bacteria have developed the necessary enzymes
and there are plenty of nutrients.
 Ideal conditions are present i.e. plenty of food,
moisture, oxygen etc.
The Stationary Phase:
• The rate of growth levels off during this period. This is
because:
 During this period there is a lack of space, moisture,
oxygen etc.
 The nutrients are becoming used up.
 The amount of waste produced by the bacteria
themselves is increasing.
 The rate at which new cells are produced is equal to
the rate at which other cells are dying.
Decline Phase(Death):
During this phase more bacteria are dying than are
being produced. This is because:
 Very few nutrients are left.
 Many bacteria are poisoned by the waste
produced by such large numbers.
Thus the rate of growth is falling.
The Survival Phase:
Normally not all bacteria die a small number may
survive as spores.
These spores survive by remaining dormant until
conditions are again suitable.
Batch and Continuous Flow
Food Processing
Note: a BIOREACTOR is a vessel in which
biological reactions take place.
Food Processing
• Modern bio-processing methods involve the use of
bacteria (and other organisms) to produce a wide
range of products.
• These include dairy products e.g. yoghurts and
cheeses, artificial sweeteners, flavourings, vitamins
and alcohol products such as wines and beers.
• It is becoming more and more common to use microorganisms as a food source, in particular as a source of
protein.
• The use of bacteria to produce edible forms of
protein is called single-cell protein (SCP) production.
Food Processing
There are two main methods of food processing
(fermentation):
• Batch food processing
• Continuous flow food processing
Batch Food Processing
• In batch food processing a fixed amount of sterile
nutrient is added to the micro-organisms in the
bioreactor.
• The micro-organisms go through the stages of a typical
growth curve i.e. the Lag, Log, Stationary and Death
stages.
• As this happens the nutrients are used up and the
product formed.
• Product normally forms at the log or stationary stage.
• Process is stopped before the death phase because
there is very little product formed at this stage.
In Batch Processing most of the product is formed during
the stages highlighted below
Lag phase
Log Phase
Stationary
Number of Bacteria
Phase
Time (days)
Death Phase
Batch Food Processing
• At the end of production the bioreactor is cleared out.
• The product is separated from the rest of the solution
and is purified.
• The bioreactor is cleaned, re-sterilised and the process
can then be repeated.
Batch processing
Continuous Flow Food Processing
• In continuous flow food processing nutrients are
continuously fed into the bioreactor.
• At the same time the culture medium (containing
some micro-organisms) is continually withdrawn.
•In this method of food processing micro-organisms are
maintained in the Log phase of growth. This means
they are growing rapidly and producing the product at a
fast rate.
• In continuous flow bioreactors factors such as
temperature, pH, rate of stirring, concentration of
nutrients, oxygen and waste products are constantly
monitored in order to maintain growth in the Log phase
and therefore produce the maximum yield.
In Continuous Flow Processing most of the product is
formed during the stage highlighted below
Log Phase
Number of Bacteria
Lag phase
Time (months)
Continuous Flow Food Processing
• Maintaining constant conditions is very difficult, as a
result this method of food processing is limited to a
small number of applications e.g.:
- production of single-cell protein
- some methods of waste water
treatments.
Continuous flow processing
Advantages of Batch Food Processing
• Easier process to control compared to continuous
flow food processing.
• Product may be needed only in small amounts.
• Product may be needed only at particular times.
• Large amount of product formed allows for some
losses during separation and purification.
• Micro – organisms grow well over short periods of
time. In continuous flow food processing long periods
of time are required which may not suit all microorganisms.