Bacterial Growth Flashcards
Bacterial Growth:
What do favourable conditions facilitate?
Cells rapidly increase in number
Binary Fission- asexual reproduction
Progenitor & Daughter
Mean Generation Time- time it takes for a bacterial cell to divide (usually measured when they are in optimal conditions) e.g. for E.coli it is 20 mins and for tubercuolcis its 22.5 hours
What are the steps in the process of binary fission?
Why might the two bacterial cells produced by binary fission not be identical?
- Cell elongates and DNA is replicated (2 copies in 1 cell)
- Cell wall and plasma membrane begin to divide (envaginates) elongation can occur from the centre or sometimes from the poles
- Cross-wall forms completely around divided DNA -some bacteria stay at this stage in a long filament
- Cell separate (2 independent bacterial cells)
The DNA in these cells should be identical but due to the lack of DNA repair and proofreading machinery many mutations prevail, allowing bacteria to evolve rapidly*
Draw a microbial growth curve
Assuming a doubling time of 30 mins
Rate of growth starts of slowly (lag phase) then increases rapidly when there are enough cells to accelerate growth (log phase)
- Lag phase
- Late lag early log
- Log/exponential phase
Population Growth Curve (closed batch envirnoment):
What does it take into account?
How do we measure growth curves?
(Bacteria grown in batch environment, fixed amount of nutrient and a fixed innoculum of bacteria-closed system)
Cell division rate changes:
- Micro environment changes occur
- Nutrients used up
- Accumulation of toxic products leads to stationary phase
- no. bacteria dividing can be manipulated
Mesured by Optical density- how light is absorbed through the medium at a particular wavelength= “how cloudy” (OD – meaused at 600nm
Population Growth Curve: How is it measured?
Optical density
- Light source goes through prism
- separates light into different wavelengths
- Passes through filter which filters out all the other wavelengths except 600nm
- Passed through sample which refracts incoming light
- Any unscatted light detected on photocell and gives us a reading on the spectrophotometer
- More bacteria= less light comes though
Incident light I0
Unscatterd light =I
OD= log (Io/I)
Describe chemostatic bacterial growth
- Chemostatic regulation of growth environment (fermentation) to prolong optimal environment by pumping in fresh medium and tap off dying bacteria, maintain bacteria in the culture at log phase
- optimum: pH, nutrient, pO2, temperature can all be maintained
- Cultures can reach much higher OD
- Used for biotechnology to produce higher levels of therapeutics
- Nutrient starvation models to see how it impacts bacterial growth
Name some Energy (ATP) Sources
- Chemotrophs e.g. Rhodobacter
They fix H2S (hydrogen sulfide) to O2 to produce hydrogen sulfate and in doing so allows them to couple the reduction of ADP and pi to ATP which can be used with CO2 produce carbohydrate (which can be metabolised)
- Phototrophs e.g. Cyanobacteria use energy from sun and CO2 to photosynthesise and as a result produce O2
Carbon sources: Autotrophs
- Require only carbon dioxide as a carbon source
- Can synthesize organic molecules from inorganic nutrients
- via Photosynthesis
Carbon sources: Heterotrophs
- Require organic forms of carbon
- Cannot synthesise organic molecules from inorganic nutrients
Classifying bacteria by their Energy & Carbon requirements
- Photoautotroph
- Chemoautotroph
- Photoheterotroph
- Chemoheterotroph
Factors Affecting Growth
Nutrients:
- Essential:
C, H, O, N, P, S
- Minor:
K, Na, Cl, Ca, Fe
- Micro:
Mg, Mb, Cu, Zn, Co
Factors affecting growth: pH (Hydrogen ion concentraion)
Bacteria will have optimal growth outside of which promote bacterial death
Factors affecting growth: Name the 3 main categories of bacteria across varying pH values
- Acidophile e.g in gastrointestinal sysyem
- Neutrophile e.g. in mouth or skin
- Alkaphile e.g in alkaline lakes
Will have an optimum pH →optimum growth closest to optimum pH
Name different species of bacteria, their minimum, optimum (cardinal) and maximum pH values
*
What is the effect of temperature on growth rate?
What can we do to ensure our food is safe to eat?
Depends on their optimum temperature values
Cook food at temperatures that kill most bacteria
Refrigerate food, dont leave it out
Freeze food to ensure no bacterial growth
Factors affecting growth: Name the main categories of bacteria across varying temperature values
From low to high temperatures:
Psychrophiles (-10-20°C)
Psychrotrophs (0-30°C)
Mesophiles (10-50°C)
Thermophiles (40-70°C)
Hyperthermophiles (65-110°C) e.g Taq (thermophilius aquaticus) polymerase
Describe the effect of temperature on population growth rate
Can this help to preserve food?
As the temperature gets further away from the optimum►Decreased number of total cells in the population (climax population) ►Increased lag which reduces the genergation time
Water Activity (Aw)
How can this consideration help to preserve food?
- Water available for metabolism
- Higher Aw supports more microorganisms
Lower end of the scale:
- Xerophilic e.g cacti
- Halophilic (thrive in high salt concentrations)
E.g drying fish out to preserve it (curing)
Oxygen Tolerance
- Oxidation/Reduction potential (redox potential/Eh)
- Obligate Aerobe:
Most fungi & yeast
- Facultative anaerobe:
- Salmonella*
- Escherichia coli*
- Obligate anaerobe:
- Clostridium*
- Microaerobic:
- Campylobacter*
- Helicobacter*
Describe the effect of oxygen on growth
(i) Obligate aerobes
(ii) Facultatuve aerobes
(iii) Obligate anerobes
(iv) Aerotolerant anaerobes
(v) microaerophiles
