1. Germination 2. Vegetative state 3. Starvation state 4. Asymmetric cell division 5. 1 copy of genome in spore and 1 in mother cell 6. maturation state 7. mother cell lyses 8. mature spore germinates

Bacterial development Flashcards by Rosie Liddell

Bacterial development

- alternative states

Spatial
= different parts of cell form different structures with different functions

Temporal
= alternative states as part of life cycle

Spatiotemporal
= combined

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Similarities and differences between stalk and swarmer cells

Same: Genome

Different: changes in gene expression

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Quorum sensing

- what is it?

Molecular system to monitor population density

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Quorum sensing

- how does it generally work?

Bacteria secrete autoinducer molecules

low conc = doesn’t do much different
high conc = changes gene expression

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Autoinducers

Peptide or small molecule

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2 proteins in the quorum-sensing system

LuxI
- synthesises autoinducers

LuxR
- transcriptional activator

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Pseudomonas aeruginosa

- low vs high density

Low = harmless type
- inactive intracellular protein receptors

High = progressive type

active receptors
produces virulence factors

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S.aureus

- low vs high density

Low
= adhesion phase

High
= invasion phase

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Steptomyces

- life cycle

Spore germinates
Vegetative mycelium
Aerial hyphae
Spore chains

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Development

- Diauxic shift

Bacteria grow on glucose until glucose exhausted

> changes in gene expression
> induces beta-galactosidase
> bacteria grow on lactose

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Endospore formation

when does it occur?
what are they?

In response to stress conditions
- desiccation, starvation + cell density

= metabolically dormant cells
- resistant to heat, desiccation, toxins + radiation

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Endospore formation

what do they enable?
when do they germinate?

Survival in adverse conditions + dispersal

When conditions are favourable

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Control of entry into sporulation

Spo0A-P produced at 2 cons

Low = Vegetative growth continues + also produces toxins + proteases etc
Doing everything it can to survive

High = starts to sporulate

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Sporulation

- genetics

~800 genes involved

Controlled by sigma factors
- controls whether genes are expressed within spore or mother cell

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Sporulation cycle

Germination
Vegetative state
Starvation state
Asymmetric cell division
1 copy of genome in spore and 1 in mother cell
maturation state
mother cell lyses
mature spore germinates

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Endospore structure

Exosporium
= thin proteinaceous layer
(some lipids + carbs)

Spore coat
= spore-specific proteins

Core wall
= normal peptidoglycan

Cortex
= unique form of peptidoglycan
= protective

Endospore structure

- what happens in the centre of the spore (core/spore protoplasm)?

Centre of spore - pH drops by 1 unit
-> produce SASPs

SASPs
= small acid-soluble spore proteins
- protect DNA from damage
- Also C + energy source during germination

Endospore germination

Activation
- germinate receptors sense a favourable enviro
(heat, rich nutrients, water)

Germination

endospore structures degraded
dipicolinic acid released

Outgrowth

swelling of core + expansion of cell
return to normal metabolic activity

Endospore stability

Metabolically inactive + can survive without nutrients, water etc.

Survive extreme temps + harsh chemical treatments

Remain dormant for yrs

Clostridium

- how it causes disease after antibiotics wipe out the microbiome

Ingest clostridium spores
Bile salts induce germination
Adheres to cells
Colonises cells + produces toxins
Forms pseudomembrane

Bascillus anthracis

- zebras

Diseased zebra dies
Spores stay in grass
New zebra eats grass
Zebra gets anthrax

Biofilms

what are they?
why are they important to bacteria?

Microbial communities typically attached to a surface
(biotic or abiotic)

Pathogenesis

Mixed biofilms

- features

Contain several different microbes

Occur naturally

Environmentally important

Monoxenic biofilms

- features

Single microbial species

Artificial

Often associated with infections

Biofilms | - e.g. Proteus mirabilis

UTI Forms biofilms in urinary tract - produces urinase crystals that block catheter

Biofilm diversity

Differs between species: >Matrix sugars + proteins >Signalling pathways >Physical forms

5 stages of biofilm formation

1. Attachment 2. Aggregation 3. Micro-colony formation 4. Maturation 5. Detachment

Stages of biofilm formation | - 1. Attachment

Requires motility + surface attachment > flagella > pili (twitching)

Stages of biofilm formation | - 4. Maturation

Further adaptation to life in a biofilm: > metabolic rate/division slows down > EPS/matrix production > AB resistance

Reasons for biofilms | - help promote growth + survival

``` > trap + concentrate nutrients > locate growth to favourable locations > prevents detachment in flowing systems > provide defence > allow community associations ```

Biofilm resistance mechanisms

Antimicrobials can't penetrate into biofilm Decreased growth rate of cells in biofilm Expression of resistance genes Some cells survive AB -> biofilm regrows (= 'persisters')

Reasons for biofilms | - allow community associations

Division of labour | - metabolic + genetic advantages

Biofilms shaped by complex chemical gradients

``` Copiotrophic biofilm - O2 gradient Aerobes at top -> Fermenters -> Anaerobes at bottom ``` Obligotrophic biofilm - Nutrient gradient Metabolically active cells at top -> dead cells at bottom pH gradient Quorum sending gradient

Biofilms shaped by complex metabolic networks

Chemical communication Electrical communication Cooperation - Nitrification Competition - ABs - cheating - nutrient depletion

2 proteins in B.subtilis

``` TasA = structural protein EPS = ECM ```

Mutant with no EPS Mutant with no tasA

No biofilm No biofilm

Combine EPS mutant + tasA mutant

Biofilm produced

How to eradicate biofilms

Develop drugs or drug therapies to disable the persister phenotype e.g. multi-drug therapy +/or cyclical applications Incorporation of drugs unto surfaces - prevent colonisation Physical disruption - ultrasound Enhance detachment - identify genes encoding biofilm destruction activities