Bacterial Population Growth

Question 1

Why do we need to study bacterial growth?

Answer 1

> human health
industry
environment

Question 2

What is the dream of a bacterium?

Answer 2

To become 2 bacteria

Question 3

How is bacteria growth different in the lab vs in the wild?

Answer 3

Lab = colonies

Wild = single cells or biofilm

Question 4

What are the 3 stages to 1 bacterium becoming 2?

Answer 4

1. cell increases in mass + volume
2. chromosome replicates + segregates
3. cell division by binary fission

Question 5

What is the acronym for the growth requirements of bacteria?

What does this stand for?

Answer 5

FAT TOM

Food
Acidity 
Time
Temp
Oxygen
Moisture

Question 6

Food

Answer 6

Rich foods e.g. chocolate
Allow fast bacterial growth

Minimal food e.g. lettuce
Provides essential nutrients
BUT bacteria have to make amino acids to grow

Question 7

Nutritional requirements for bacterial growth

Answer 7

Sources:
C
N
H
O
S
P
O

Essential amino acids
Essential vitamins + minerals

Question 8

Heterotrophy

Answer 8

= must provide bacteria with C source

Question 9

Autotrophy

Answer 9

= can produce C from photosynthesis

e.g. cyanobacteria

Question 10

Acidity

Answer 10

Those living in low or high pH must provide a mechanism for protecting from damage

Question 11

Time

Answer 11

Need to give bacteria time to grow

E.g. E.coli take 20mins to divide
Due to replication of chromosomes happening at multiple levels
= multi forked chromsome

Question 12

Temperature

Answer 12

37 degrees = enzymes most functional

Fluidity of cell membrane

• decreases in cold
• > bacteria change phospholipids to keep it more fluid

Cold-loving bacteria
- also produce anti-freeze proteins

Question 13

Names of bacteria types based on temp

Answer 13

Psychrophiles
= -5 - 20

Mesophiles
= 15 - 45

Thermophiles
=45 - 80

Hyperthermophiles
= 65 - 105

Question 14

Extremophiles

Answer 14

Thermophile

Psychrophile = ice

Alkaliphiles

Halophile = high salinity

Xerophile

Question 15

What do bacteria that live in radioactivity need?

Answer 15

Mechanisms to cope with not gaining many mutations

- better proofreading principles

Question 16

Oxygen

Answer 16

Those that have evolved to grow in O2

- have evolved systems to get rid of free radicals (hydroxyl ions)

Question 17

Moisture

Answer 17

Sufficient level required

Question 18

5 names of bacteria based on O2 requirements

Answer 18

Obligate aerobe

Micro-aerophile = requires small amounts of O2 –> too much = dies

Facultative anaerobe
= will survive with or without O2 + still divide

Aerotolerant anaerobe
= will survive without O2 but can’t divide

Obligate anaerobe

Question 19

Water

- system needed

Answer 19

Need a system that allows maintenance of osmotic potential in cell

e.g. produce large amounts of proline -> stops water going out of cell

Question 20

Water

Answer 20

Some bacteria can replace their water with other molecules

• compatible solutes or osmolytes
• counterbalances osmotic imbalance + often provides other protective functions

Question 21

Fastidious bacteria

Answer 21

Only grows when conditions are perfect
e.g. require supplements to media or specific gases

Grow and replicate slowly
Hard to grow

Question 22

Salmonella

Answer 22

Reduces H sulphate to tetrathionate

• > used as an e acceptor
• > outcompetes all other bacteria

Question 23

5 phases of standard growth curve

Answer 23

1. inoculation
2. lag phase
3. exponential phase
4. stationary phase
5. decline/death phase

Question 24

Lag phase

Answer 24

Time to adapt to new enviro + prepare for growth

Accumulating:
>Catabolites
>Anabolic metabolites
>Gene expression + protein synthesis of necessary enzymes

Repairing any damage

Question 25

Length of lag phase

Answer 25

Depends on condition of innculum + nature of new media

Varies between species/strains

Question 26

Log/exponential phase

Answer 26

Cells growing + dividing rapidly

Constant growth rate
OD600 + viable count rises exponentially

Slope depends on species + culture conditions

Question 27

Use of log/exponential phase

Answer 27

Sub-culturing now will minimise subsequent lag phase

Used experimentally for study of enzymes, gene expression etc.

Question 28

Stationary phase

Answer 28

Slow growth + division

OD600 + viable count plateau

Due to decreasing amounts of nutrients &/or increasing conc of waste
e.g. growing on glucose produces lactic acid -> lowers pH

Question 29

‘Hibernation state’

Answer 29

Stationary phase

Metabolic activity slows down greatly/stops

Question 30

Cryptic growth

Answer 30

Cell division = cell death

Question 31

What happens in stationary phase in the wild?

Answer 31

Don’t live alone

• > Start to produce anti-biotics
• > kills competition

Question 32

Death phase

Answer 32

1+ essential nutrients exhausted
OR 1+ wastes reached lethal toxic levels

Viable count decreases

OD600 decreases (cell lysis)

Question 33

Growth rate

Answer 33

Change in cell no. per unit time

Unit: generations/hour

(Can be fractional)

Question 34

Generation time/doubling time (g)

Answer 34

Time taken for population of cells to double in no.

(=time taken per cell doubling)

Doubling time varies for species + culture conditions

Question 35

Biphasic growth

AKA diauxic shift

Answer 35

Exposure to 2 nutrients

• preferential use of 1
• > then runs out
• > alters its metabolism to make use of 2nd

Can get multiauxic effects

Question 36

What is biphasic growth usually due to?

Answer 36

Catabolite repression

e.g. glucose, while present, represses the expression of lactose catabolic genes (beta-galactosidase)