Bacterial Physiology Flashcards
Bacterial growth:
increase in number of cells, not cell size
- one bacterial cell - - - > millions of clone cells : colony
Cell division :
binary fission
Generation time :
time taken by the bacterial population to double. Vary according to bacterial species, culture/environmental conditions
Equation: N (number of cells)= N0
x 2n n : number of generation
explain two types of culture media
1.Liquid(usually for pure culture)
2.Semi solid or Solid (agar
isolation, plate count,…)
What do bacteria need to grow ?
Not including environmental conditions
Energy
- Nutrients :
- Macro elements:
- C, O, H, N, S, P (g/L)
- K+,Ca2+, Mg2+, Fe2+ (mg/L)
- Micro elements:
- Co, Cu, Mb, Mn, Ni, Zn (µg/L)
Complex/undefined media :
Contain complex ingredients (e.g yeast extracts: many chemical
species in unknown proportions) : not all the chemical
compounds are known.
Minimal (synthetic) media :
All the chemical compounds are known. The concentration of
each ingredient is precisely known (defined media). Contains the
minimum nutrients possible for colony growth.
When do we call and organism an Auxotrophic/prototrophic
inability of an organism to synthesize a particular organic
compounds required for its growth (growth factor). This compound needs to
be added in the medium. (Opposite : prototrophy
Growth factor:
organic compounds that are essential for the bacterial growth
(e.g amino acids, vitamins, nucleotides)
How do we measure bacterial growth ?
- Turbidity : DO580
- Plate counts : N (number of viable bacteria /mL)
- Dry weight : X (g/L)
Name the Growth phases in batch cultures (the nutrients are not renewed)
1 lag phase 2 acceleration phase 3 log or exponential phase 4 slow down phase 5 stationary phase 6 decline or death phase
Describe Growth phases in batch cultures (the nutrients are not renewed)
Equation :
lnN = µ(t-t0) + lnN0
(Or logN = (µ/2,3) (t-t0)+ logN0)
N: viable bacteria (cfu/mL) at a time
t = time (h)
µ : growth rate (h-1
)
If LN2 = 2N1 —>
Hint: (t2-t1 time required to double the population) :
provide the growth rate formula
generation time : G
µ = Ln2/G
Explain what a Lag phase is
Adaptation (e.g the bacteria synthetize new enzymes in response to new medium)
µ = 0
The length of the phase depends on:
- Inoculum (species, metabolic state, stress)
- Culture medium
- Physicochemical factors (e.g T°C)
Sometimes no lag phase (especially if inoculum in exponential phase and pre culture and
culture in the same conditions (medium, T°C, etc…)
- Acceleration phase
Transition phase
µ increases progressively
- Log or exponential phase
µ max and constant µ and G can be determined µ and G depend on : - Species - Medium - Physicochemical conditions
Slow down phase
Transition phase
µ decreases progressively
What factors causes Stationary phase
growth ceases but cells remain metabolically active
May be due to :
- Disparition of a nutrient (macro or microelement, growth factor for which the
bacteria is auxotrophic) : limiting factor
- Accumulation of toxic metabolites/ modification of some physicochemical
parameters such as pH (lowering) or osmotic pressure
- Accumulation of toxins produced by the bacteria
what is the growth rate during the Decline or death phase, what causes decline or death phase?
µ < 0 Cell death exceeds division Depletion of nutrients Accumulation of toxic metabolites Cell lysis due to endogenous proteolytic enzymes
obligate aerobes :
O2 required (Pseudomonas)
microaerophiles :
O2 required in low concentration
facultative anaerobes :
can grow without O2 but greater growth in presence of O2 (E. coli)
- aerotolerant anaerobes:
don’t need O2 but tolerate O2 (Enterococcus)
obligate anaerobes**
cannot tolerate O2 (Clostridium)
pH
pH measures the hydrogen ion activity in a solution
Internal pH usually around neutral
pH impacts plasma membrane integrity and nutrient availability
Each organism can grow within a given pH range and has a optimum pH
- acidophiles ,neutrophiles,alkaliphiles
Temperature
Temperature impacts membrane fluidity and the speed of enzymatic reactions
- psychrophiles 0°C <15°C (optimum) <20°C
- psychrotrophes or psychrotolerants 0°C <20°C (optimum) <30°C.
- mesophiles 15 à 20°C < 40°C (optimum) < 45°C
- thermophiles 45°C <55°C (optimum) < 65°C
- hyperthermophiles (optimum around or above 80°C)
Osmotic pressure
: the pressure that would be required to stop the flow of
solvent molecules (water molecules) from a dilute solution to a concentrated
solution through a semi-permeable membrane (plasma membrane).
Atmospheric pressure
Microorganisms inhabiting the deep-sea and subsurface of Earth for example are able to survive at pressures
greater than 1 atmosphere.
Radiation
Some microorganisms can withstand high doses of radiation
Inhibit or prevent growth of microorganisms
Chemical agents:
- Killing microorganisms : e.g Bactericides, fungicides
- Inhibiting the growth of microorganisms : e.g bacteriostatics
Antibiotics : secondary metabolites produced by microorganisms that can kill or inhibit
the growth of bacteria. Different targets : bacterial cell wall, protein synthesis, etc …
Antiseptic : stops or slows down the growth of microorganisms. Applied to living tissues
Disinfectant : applied to non-living objects in order to inactivate or destroy
microorganism
Inhibit or prevent growth of microorganisms
Physical agents:
Sterilization :
complete destruction or elimination of all viable organisms in or on a substance
being sterilized
Heat
Parameters : Type of heat, time of application and temperature
Irradiation
- Ultraviolet light : target DNA (185 and 260 nm)
- Gamma and electron beam radiations : ionizing radiations. (short
wavelength / high energy)
Filtration
Physical removal (exclusion) of the microorganisms in a liquid or a gaz (0.22 µm
filter for bacteria
explain method of plate assays
- performing serial dilutions of the inoculum then spreading it and counting the viable bacteria/ ml
CFU/ml formula
no of colonies x dilution factor x volume
