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MBY365 Theme 3 summary
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Full summary of theme 3 (microbial interaction at the community level) made using lecture notes and class notes.
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ENVIRONMENTAL E. COLINICHES OF E. COLI
- The mammalian gut is not the only niche in which E. coli can grow
- Specific strains can grow and thrive in the external environment
- The ability to survive and grow in the environment is linked to specific strains
or genotypes
- The primary habitat is the lower intestines of warm-blooded animals
- The secondary habitat is water, sediment, soil - they have a negative growth
rate here
- Is discharged into the environment through faeces or wastewater effluent
- Presence of E. coli in water is considered an indicator of faecal pollution
- Primary habitat
- Temperature range of 34-37℃
- pH 6.8
- Low redox potential
- Moist and dark
- Contain 500 other species - 1011-1012 cells per gram of faeces
- Secondary habitat
- High variation in pH, oxygen, temperature and moisture
- Exposure to sunlight
- Predators
- Exposure to other species
- Naturalised E. coli genotypes are distinct from animal-host origin E. coli
genotypes
FACTORS AFFECTING GROWTH
- Growth and survival of E. coli in natural environments can be influenced by
both biotic and abiotic factors
- Abiotic factors
- Salinity
- Solar radiation
- Temperature
- Moisture
- Nutrient availability
- pH
- Biotic factors
- Competition
- Growth limiting nutrient (energy sources)
- Ability to utilise resources (sites)
- Predation - flagellates and small ciliates/protists
- Target gram negatives and suspended bacteria
, - Temperature
- Is the most important factors influencing E. coli survival and growth
- Can grow in soil below 30℃
- Their death rate is faster in warm (>30℃) than cold (<15 ℃)
temperatures
- Survival in temperature-fluctuating conditions may vary by genotype
- Larger amplitudes of fluctuation reduce growth more than smaller
amplitudes
- Water availability
- Desiccation is one of the common stresses to bacteria in natural
environments
- Rehydration can cause an anoxic environment around the cells
- Bacteria need to adjust their membranes and gene regulation to adapt
to the desiccation and rehydration cycles
- Nutrient availability
- E.g. carbon, nitrogen and phosphorus
- Natural environments are generally low in readily available nutrients
- E. coli shows catabolic flexibility under glucose-limited conditions
resulting in the efficient uptake of diverse carbon sources
- This versatility and flexibility in carbon sources allows E. coli to survive
and grow in the environment
- pH
- Level of pH resistance varies by strains
- Specific E. coli strains could survive selectively
- Solar radiation
- Is the most effective abiotic factor causing death of FIB in
environmental waters
- It inactivates important chemical pathways
- Low wavelength solar radiation can cause DNA damage and oxidation
of cellular contents - only on upper surface of water
- Effect of sunlight varies by isolation time or turbidity of the water
- Presence of other microorganisms
- E. coli can be predated by protozoa and lysed by phages
- Also needs to compete with indigenous micro-organisms for limited
nutrient sources
- E. coli grows much better in sterile vs non-sterile soils
- Ability to form biofilms
- Biofilms contribute to the persistence of E. coli in natural environments
- They protect the bacteria from hostile environmental conditions such as
UV radiation, desiccation, protozoan predators and chemicals
- Also provide bacteria with a source of nutrients
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