Bacterial Physiology

Question 1

Bacterial growth:

Answer 1

increase in number of cells, not cell size

- one bacterial cell - - - > millions of clone cells : colony

Question 2

Cell division :

Answer 2

binary fission

Question 3

Generation time :

Answer 3

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

Question 4

explain two types of culture media

Answer 4

1.Liquid(usually for pure culture)

2.Semi solid or Solid (agar
isolation, plate count,…)

Question 5

What do bacteria need to grow ?

Not including environmental conditions

Answer 5

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)

Question 6

Complex/undefined media :

Answer 6

Contain complex ingredients (e.g yeast extracts: many chemical
species in unknown proportions) : not all the chemical
compounds are known.

Question 7

Minimal (synthetic) media :

Answer 7

All the chemical compounds are known. The concentration of
each ingredient is precisely known (defined media). Contains the
minimum nutrients possible for colony growth.

Question 8

When do we call and organism an Auxotrophic/prototrophic

Answer 8

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

Question 9

Growth factor:

Answer 9

organic compounds that are essential for the bacterial growth
(e.g amino acids, vitamins, nucleotides)

Question 10

How do we measure bacterial growth ?

Answer 10

1. Turbidity : DO580
2. Plate counts : N (number of viable bacteria /mL)
3. Dry weight : X (g/L)

Question 11

Name the Growth phases in batch cultures (the nutrients are not renewed)

Answer 11

1 lag phase
2 acceleration phase
3 log or exponential phase
4 slow down phase
5 stationary phase
6 decline or death phase

Question 12

Describe Growth phases in batch cultures (the nutrients are not renewed)
Equation :

Answer 12

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
)

Question 13

If LN2 = 2N1 —>
Hint: (t2-t1 time required to double the population) :
provide the growth rate formula

Answer 13

generation time : G

µ = Ln2/G

Question 14

Explain what a Lag phase is

Answer 14

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…)

Question 15

2. Acceleration phase

Answer 15

Transition phase

µ increases progressively

Question 16

3. Log or exponential phase

Answer 16

µ max and constant
µ and G can be determined
µ and G depend on :
- Species
- Medium
- Physicochemical conditions

Question 17

Slow down phase

Answer 17

Transition phase

µ decreases progressively

Question 18

What factors causes Stationary phase

Answer 18

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

Question 19

what is the growth rate during the Decline or death phase, what causes decline or death phase?

Answer 19

µ < 0
Cell death exceeds division
Depletion of nutrients
Accumulation of toxic metabolites
Cell lysis due to endogenous proteolytic enzymes

Question 20

obligate aerobes :

Answer 20

O2 required (Pseudomonas)

Question 21

microaerophiles :

Answer 21

O2 required in low concentration

Question 22

facultative anaerobes :

Answer 22

can grow without O2 but greater growth in presence of O2 (E. coli)

Question 23

• aerotolerant anaerobes:

Answer 23

don’t need O2 but tolerate O2 (Enterococcus)

Question 24

obligate anaerobes**

Answer 24

cannot tolerate O2 (Clostridium)

Question 25

pH

Answer 25

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

Question 26

Temperature

Answer 26

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)

Question 27

Osmotic pressure

Answer 27

: 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).

Question 28

Atmospheric pressure

Answer 28

Microorganisms inhabiting the deep-sea and subsurface of Earth for example are able to survive at pressures
greater than 1 atmosphere.

Question 29

Radiation

Answer 29

Some microorganisms can withstand high doses of radiation

Question 30

Inhibit or prevent growth of microorganisms

Answer 30

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

Question 31

Inhibit or prevent growth of microorganisms

Answer 31

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

Question 32

explain method of plate assays

Answer 32

1. performing serial dilutions of the inoculum then spreading it and counting the viable bacteria/ ml

Question 33

CFU/ml formula

Answer 33

no of colonies x dilution factor x volume