1 - BACTERIAL GROWTH Flashcards
(25 cards)
Bacteria undergo developmental change due to environment not genetic factor. What kind of developmental change?
Stationary phase and endospore formation - (Bacillius aerobe, Clostridim anaerobe)
Hallmark of bacteria:
SPEED of growth
E.coli + minerals, glucose, optimal temp = td =
40 min 20 mins rich complex media
Characteristics of Log phase
Characteristic rate under environmental conditions.
Growth unrestricted as long as nutrients don’t become limiting + toxins don’t accumulate to inhibitory level
What reaction does log phase mimic?
First Order Autocatalytic reaction
Specific Growth rate (mu/k) =
(logX - logX0)2.303/ t - t0
Doubling time/ generation time =
0.693/mu k
What is balanced growth?
All cell constituents increase by the same proportion, can occur for long time in lab but often naturally growth is unbalanced. We like to study bacteria in balanced growth.
Why study bacteria in balanced growth?
1) samples at time points = identical
2) relative rate of synthesis of a constituent can be known by measuring growth rate - same for all (MEAN cell size = same)
3) most reproducible physiological state - allow repeat experiments
Why do bacteria stop growing?
Use up key nutrient, O2 too low, taxi metabolic product
Type of growth curve seen as growth stops depends on reason for stopping
A Sharp transition to SP = running out of a single limiting nutrient
B Slower gradual transition to SP = simultaneous starving or toxic end product accumulation
Adaption changes transition
Growth in Stationary phase is
unbalanced - cell constituents do not have constant composition
DNA:protein ratio in SP
DNA:protein ratio change in SP - DNA actively synthesised, protein synthesis decelerated - cells smaller. in SP
How does cell size change in SP?
Cell size becomes smaller in SP via reductive cel division
Evidence for reductive cell division
Cell mass stops increasing, viable and total cell no. continue to increase further due to reductive cell division
Why do cells undergo reductive cell division?
Increase the clonal population - increase chance of survival
Lag phase:
Adaptive phase. Inoculate actively growing cells into a new different media they will undergo a lag phase to adapt, no lag phase if exact same media.
Length of lag is variable
Apparent Lag phase
Dead cells can dominate measures of the no. of cells (e.g. OD) can lead to misinterpretation of lag phase
Growth yield
Growth yield ∝ [ limiting nutrient ]
Linear relationship between conc and growth yield - hold for nearly all nutrients and concs
Bf - Bo =
Y ( CO - C)
Y =
(Bf - Bo)/( CO - C)
Growth yield used to make intelligent guesses about bacterium energy metabolism. How?
1) Macromolecular polymérisation ATP needed - amount is very consistent, same under environments/conditions
2)Amount of MM produces ∝ yield
Balances growth ^ yield = ∝ ^constituents in cell
Growth yield (Y) is an index of ATP generation
Specific oxygen consumption (Q02) does not vary consistently with growth rate. From this can conclude:
The total energy for doubling cell mass decreases in proportion to the growth rate.
Growth rate set by the energy requirements for the synthesis of monomers
- Energy cell needs for polymerisation = constant
- But cell growing at low growth rate = small amount fo MM
- Must have energy available for other purposes
- > monomer synthesis - aa, purines
If we want cells to grow fast supply them with:
Monomers
Not supplied = low growth rate requires extra energy
