Microbial growth and physiology Flashcards
Nutrient requirements
Energy carbon nitrogen inorganic elements gases (oxygen and hydrogen) water
nutrient requirements
Carbon source
Carbon dioxide (autotroph)
Organic compounds e.g. glucose (heterotroph)
nutrient requirements
Energy source
Sun i.e. photosynthesis (phototroph)
inorganic elements e.g. NH3
OR
organic compounds oxidised aerobically or anaerobically (chemotroph)
nutrient requirements
Electron source
(e removed from donor, passed to acceptor releasing energy; donor is oxidised)
inorganic electron donor e.g. H (lithotroph)
organic electron donor e.g. glucose (organotroph)
requirements - oxygen
5 points
- aerobes - require oxygen
- obligate anaerobes - must have no oxygen
- facultative anaerobes - can survive with no oxygen
- aerotolerant anaerobes - anaerobes tolerate oxygen
- microaerophiles - require oxygen at very low concentration
microbial growth
single celled microorganisms divide by binary fission (doubling)
1 cell = 2.
2 cells = 4. so on…
exponential increase when ready supply of nutrients (increase in size at constantly growing rate)
increase in cell number by generation
generation 1 = 2 to power of 1 = 2 2 = 2 to power of 2 = 4 3 = 2 to power of 3 = 8 4 = 16
converting exponential growth curve into straight line
plotting logarithm (log) of the number of cells against time
Microbial growth curve
4 phases
- Lag phase
- log (exponential phase)
- stationary phase
- death phase
Microbial growth curve
lag phase
organism adapting to its new environment; enzymes synthesised, cells increasing in size but not yet dividing
Microbial growth curve
Log (exponential) phase
cells undergoing exponential growth with constant growth rate and mean generation time. Slope and length of log phase depend on how well medium meets requirements
Microbial growth curve
Stationary phase
no net increase in cell number; nutrient (or oxygen) exhausted, environment changed (pH), toxic products accumulate
Microbial growth curve
Death phase
cells die (often exponential); no energy, pH damage, toxic products
Batch culture
When microbes are inoculated into a fixed volume of growth medium in a closed system
continuous culture
4 points
- Permanently in log phase of growth
- New nutrient added at same rate that culture mixture removed from growth vessel
- Should achieve steady state
- Can maximise production of microbe and its products
Industrially important
chemostat
equipment for continuous culture of micro-organisms
Growth of micro-organisms on solid medium
6 points
- Cannot count cell numbers
- bacteria colony spreads out to obtain nutrients from agar
- Change in diameter of colony shows similar growth curve to cell numbers in liquid medium
- Growth on solid medium usually slower than liquid medium
- For fungi growth radiates out from initial spore – roughly circular growth
- Diameter of colony shows similar curve as cell numbers of unicellular micro-organisms
biofilms
4 points
- Microbial growth on solid material in the environment often takes the form of biofilms
- Need moisture, a source of nutrients and a surface
3. Steps: Attachment (to surface) Exopolysaccharide production (cements biofilm together) Maturation Dispersal
- Can excrete molecules which attract other microbes increasing size and complexity of the biofilm
e. g. microbial growth in pipes or on rocks
Counting in liquid media – “direct” count
9 points
- Use a counting chamber e.g. “haemocytometer”
- Glass slide has grid with precision engraved squares of known area
- Add a coverslip and flood slide with culture (may need to be diluted first)
- Known depth between grid and coverslip
- Count number of cells in a square (for several squares)
- Calculate average number of cells per square
- Calculate volume of liquid above each square
- Know average cells in a given volume
- Calculate cells/ml diluted culture
Counting on solid media – “viable” count
5 points
- Use either the pour plate or spread plate technique to enable colonies to be seen
- Need to dilute original sample to ensure a good number of clearly separated colonies which can be counted
- Use “serial dilutions”
- Quantitative so must use accurate volumes
- Common serial dilutions are 1 in 10 or ten-fold dilutions – each dilution is one-tenth of the concentration of the previous one. [Other common serial dilutions are 1 in 2, 1 in 5, 1 in 100]
