Lecture 3 - The two sides of bacterial endospores Flashcards
If nutrient depletion occurs or a physical stress occurs then the bacteria can respond in one of three ways:
Cell death
Go into a protective dormancy which is going into a metabolically less active state which may also eventually lead to cell death
Some bacteria are able to form endospores which are a survival structure
Most endospores dorm in
gram positive rods, commonly microbes in the soil as they are subjected to stresses all the time
Examples = Bacillus anthracis (anthrax), clostridium perfringens (gangrene), c.tetani (tetanus), c.botulinum (food poisioning) - these are medically significant bacteria that form endospores
Endospores allow..
for a dormant state during times of stress, they form within the cell
Endospore formation outcome
It is not a reproductive process we are just having one cell give rise to one endospore in this metabolically dormant survival state - survival not replication
Process …
Endospores - layers of protective coverings around the dormant genetic material - formation of this takes around 8 hours - germination of endospores takes about 15 minutes
If there are stresses going on in the bacterial environment during this time, this bacterial cell might still die but this is worth the risk
Formation process
Vegetative cell dividing by binary fission, genetic material i.e. DNA replicated
Septum forms diving the cell asymmetrically - smaller side will become the endospore - larger part becomes mother cell which helps build protective layers before dying
Larger compartment engulfs smaller compartment which forms the forespore (precursor)
Content and coat formed, dehydration
Lysis of cell and release of the endospore
Structure of the endospore
Structure of the endospore - all of the layers mean that the endospore can sit in harsh conditions and handle the environment until germination conditions become optimum
(inner most layers) Core, inner membrane, germ cell wall/core wall = contain normal cell structures such as DNA and ribosomes but it is metabolically inactive, very low water content
- Called the germ cell wall as it contains the peptidoglycan that will form the wall of the vegetative cell that grows out of the spore following germination
Cortex, outer membrane = made up of peptidoglycan but it is less cross linked than that of vegetative cells
Cortex may occupy as much as half the spore volume
Outer membrane is a phospholipid bilayer
Coat = composed of several protein layers and can be very thick, impermeable and it is responsible for the endospore’s resistance to chemicals, UV rays etc.
Exosporium = thin outer layer mainly lipids, carbohydrates, and proteins which acts like a shell that gives the final protection, made up of glycoproteins
(inner most layers) core, inner membrane, germ cell wall/core wall
(inner most layers) Core, inner membrane, germ cell wall/core wall = contain normal cell structures such as DNA and ribosomes but it is metabolically inactive, very low water content
- Called the germ cell wall as it contains the peptidoglycan that will form the wall of the vegetative cell that grows out of the spore following germination
Cortex, outer membrane
Cortex, outer membrane = made up of peptidoglycan but it is less cross linked than that of vegetative cells
Cortex may occupy as much as half the spore volume
Outer membrane is a phospholipid bilayer
Coat
Coat = composed of several protein layers and can be very thick, impermeable and it is responsible for the endospore’s resistance to chemicals, UV rays etc.
Exosporium
Exosporium = thin outer layer mainly lipids, carbohydrates, and proteins which acts like a shell that gives the final protection, made up of glycoproteins
What determines resistance in the endospore
Physical
Coat (thick layers)
Inner membrane (impermeable)
Chemical (core)
Low water content (15%, compared to >80% in vegetative cells) - Low water content in core of endospore makes the core a gel like texture and this immobilises the proteins and nucleic acids until they are needed for sporilation
Lower pH
Slightly lower than a vegetative cell
High content of dipicolinic acid and Ca2+ - Combine to form a lattice structure and the lattice structure complexes between the bases of the DNA and stabilises it. This cross linking structure in the core represents about 10% of the dry weight of the endospore
Small acid-soluble proteins
These bind to the DNA and when they bind they alter the conformation of the DNA slightly and protect it from damage
Chemical (cortex)
Decreased peptidoglycan cross linking index = 2.9% in endospore (33% in vegetative cells)
This modified peptidoglycan wall is required for the maintenance of spore coat dehydration, and the accompanying metabolic dormancy and heat resistance - it is one more layer, giving the total effect of a very resistant structure
Endospore germination
Activation - Preparing cells for germination
Germination - Swells and takes on water, breaks the spore coat which causes a loss of resistance for all the stresses in the environment but also an increase in metabolic activity in the bacteria
Outgrowth - Spore emerges from broken coat and develops into an active bacterial cell that can undergo binary fission
Endospores are the …
benchmark for physical and chemical control mechanisms
if endospores are killed then other microbes have also been killed
Why do we need to control microbial growth?
Without it we would be subjected to more widespread outbreaks of disease, contamination, pollution and spoilage
Death of microbes
loss of ability to multiply under any known conditions
Sterilisation
complete removal or destruction of all microorganisms (includes spores too) from inanimate objects. It is brought about by the use of physical or chemical methods. Non-selective
Disinfection
(removal of infection) destruction or removal of microorganisms (but not bacterial endospores) on inanimate objects by physical or chemical means
