1 - BACTERIAL GROWTH

Question 1

Bacteria undergo developmental change due to environment not genetic factor. What kind of developmental change?

Answer 1

Stationary phase and endospore formation - (Bacillius aerobe, Clostridim anaerobe)

Question 2

Hallmark of bacteria:

Answer 2

SPEED of growth
E.coli + minerals, glucose, optimal temp = td =
40 min 20 mins rich complex media

Question 3

Characteristics of Log phase

Answer 3

Characteristic rate under environmental conditions.

Growth unrestricted as long as nutrients don’t become limiting + toxins don’t accumulate to inhibitory level

Question 4

What reaction does log phase mimic?

Answer 4

First Order Autocatalytic reaction

Question 5

Specific Growth rate (mu/k) =

Answer 5

(logX - logX0)2.303/ t - t0

Question 6

Doubling time/ generation time =

Answer 6

0.693/mu k

Question 7

What is balanced growth?

Answer 7

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.

Question 8

Why study bacteria in balanced growth?

Answer 8

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

Question 9

Why do bacteria stop growing?

Answer 9

Use up key nutrient, O2 too low, taxi metabolic product

Question 10

Type of growth curve seen as growth stops depends on reason for stopping

Answer 10

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

Question 11

Growth in Stationary phase is

Answer 11

unbalanced - cell constituents do not have constant composition

Question 12

DNA:protein ratio in SP

Answer 12

DNA:protein ratio change in SP - DNA actively synthesised, protein synthesis decelerated - cells smaller. in SP

Question 13

How does cell size change in SP?

Answer 13

Cell size becomes smaller in SP via reductive cel division

Question 14

Evidence for reductive cell division

Answer 14

Cell mass stops increasing, viable and total cell no. continue to increase further due to reductive cell division

Question 15

Why do cells undergo reductive cell division?

Answer 15

Increase the clonal population - increase chance of survival

Question 16

Lag phase:

Answer 16

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

Question 17

Apparent Lag phase

Answer 17

Dead cells can dominate measures of the no. of cells (e.g. OD) can lead to misinterpretation of lag phase

Question 18

Growth yield

Answer 18

Growth yield ∝ [ limiting nutrient ]

Linear relationship between conc and growth yield - hold for nearly all nutrients and concs

Question 19

Bf - Bo =

Answer 19

Y ( CO - C)

Question 20

Y =

Answer 20

(Bf - Bo)/( CO - C)

Question 21

Growth yield used to make intelligent guesses about bacterium energy metabolism. How?

Answer 21

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

Question 22

Specific oxygen consumption (Q02) does not vary consistently with growth rate. From this can conclude:

Answer 22

The total energy for doubling cell mass decreases in proportion to the growth rate.

Question 23

Growth rate set by the energy requirements for the synthesis of monomers

Answer 23

• 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

Question 24

If we want cells to grow fast supply them with:

Answer 24

Monomers

Not supplied = low growth rate requires extra energy

Question 25

Growth rate is a function of [S] only at low S levels. What equation did Monod propose?

Answer 25

mu/k = kmaxC/Ks+C
Ks = constant substrate conc where k = max/2