Bacterial Population Growth Flashcards by Rosie Liddell

Why do we need to study bacterial growth?

> human health
industry
environment

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What is the dream of a bacterium?

To become 2 bacteria

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

Lab = colonies

Wild = single cells or biofilm

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What are the 3 stages to 1 bacterium becoming 2?

cell increases in mass + volume
chromosome replicates + segregates
cell division by binary fission

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What is the acronym for the growth requirements of bacteria?

What does this stand for?

FAT TOM

Food
Acidity 
Time
Temp
Oxygen
Moisture

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Food

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

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Nutritional requirements for bacterial growth

Sources:
C
N
H
O
S
P
O

Essential amino acids
Essential vitamins + minerals

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Heterotrophy

= must provide bacteria with C source

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Autotrophy

= can produce C from photosynthesis

e.g. cyanobacteria

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Acidity

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

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Time

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

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Temperature

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

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Names of bacteria types based on temp

Psychrophiles
= -5 - 20

Mesophiles
= 15 - 45

Thermophiles
=45 - 80

Hyperthermophiles
= 65 - 105

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Extremophiles

Thermophile

Psychrophile = ice

Alkaliphiles

Halophile = high salinity

Xerophile

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What do bacteria that live in radioactivity need?

Mechanisms to cope with not gaining many mutations

- better proofreading principles

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Oxygen

Those that have evolved to grow in O2

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

Moisture

Sufficient level required

5 names of bacteria based on O2 requirements

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

Water

- system needed

Need a system that allows maintenance of osmotic potential in cell

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

Water

Some bacteria can replace their water with other molecules

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

Fastidious bacteria

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

Grow and replicate slowly
Hard to grow

Salmonella

Reduces H sulphate to tetrathionate

> used as an e acceptor
> outcompetes all other bacteria

5 phases of standard growth curve

inoculation
lag phase
exponential phase
stationary phase
decline/death phase

Lag phase

Time to adapt to new enviro + prepare for growth

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

Repairing any damage

Length of lag phase

Depends on condition of innculum + nature of new media

Varies between species/strains

Log/exponential phase

Cells growing + dividing rapidly

Constant growth rate
OD600 + viable count rises exponentially

Slope depends on species + culture conditions

Use of log/exponential phase

Sub-culturing now will minimise subsequent lag phase

Used experimentally for study of enzymes, gene expression etc.

Stationary phase

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

‘Hibernation state’

Stationary phase

Metabolic activity slows down greatly/stops

Cryptic growth

Cell division = cell death

What happens in stationary phase in the wild?

Don’t live alone

> Start to produce anti-biotics
> kills competition

Death phase

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

Viable count decreases

OD600 decreases (cell lysis)

Growth rate

Change in cell no. per unit time

Unit: generations/hour

(Can be fractional)

Generation time/doubling time (g)

Time taken for population of cells to double in no.

(=time taken per cell doubling)

Doubling time varies for species + culture conditions

Biphasic growth

AKA diauxic shift

Exposure to 2 nutrients

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

Can get multiauxic effects

What is biphasic growth usually due to?

Catabolite repression

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

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Bacterial Population Growth Flashcards

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