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Bacterial differentiation and sporulation Flashcards

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1
Q

what 4 basic functions does bacterial differentiation result in cells having?

A
  1. stress survival
  2. physiological specialisation
  3. cell dispersal
  4. symbiotic relationship
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2
Q

what is bacterial stress survival?

A
  • the conversion of cells into resting cells with low metabolic activity and high resistance to stress
  • e.g bacillus endospores
  • acquires resistance to heat, radiation
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3
Q

what is bacterial physiological specialisation?

A
  • the occurrence and formation of cells that possess physiological features complimentary to the normal vegetative cells
  • e.g. Myxobacterial fruiting bodies, cyanobacteria heterocysts
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4
Q

what is bacterial cell dispersal?

A
  • production of cells that move either actively use flagella or surface-associated motility, or passively by wind, water or animals
  • e.g. Caulobacter swarmer cells can develop flagella
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5
Q

what is a bacterial symbiotic relationship?

A
  • interaction with other cells which leads to the establishment of kinship and symbiotic behaviours
  • e.g. Rhizobium originally appear like E. coli with a flagellum, but in nodulation they change dramatically to support nitrogen fixation
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6
Q

what are Myxococcus xanthus bacteria?

A
  • they are known as social bacteria - they interact with each other and show coordinated behaviour to survive stresses
  • when grown, they form groups of cells called rafts which are motile and leave slime trails behind
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7
Q

what are the genetic characteristics of Myxococcus xanthus?

A
  • 10Mb large genome - has excess genes compared to E. coli which is 5Mb
  • 200 TCS
  • 181 transcriptional regulators
  • 100 serine/threonine kinases for signalling (E. coli have none of these)
  • 43 sigma factors
  • 8 chemosensory systems
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8
Q

why is Myxococcus xanthus a good model organism to study?

A
  • Biofilm formation
  • Developmental differentiation, cell death, kinship, altruism and cooperation
  • Type IV pili
  • Horizontal gene transfer
  • Bacterial motor systems
  • Prokaryotic signalling processes
  • Antibiotics and therapeutica production – secondary metabolites -
  • Biological pest control
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9
Q

what is the development of M. xanthus when nutrients are available?

A
  • the bacteria grow and expand in a swarm
  • swarms are millions of organisms which move and cooperatively feed on other bacteria - act as predators
  • they use motor systems to migrate and actively hunt prey
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10
Q

what is the development of M. xanthus in low nutrient availability/starvation?

A
  • the swarm begins to contract and form mound aggregates
  • eventually they mature into fully-fledged fruiting bodies

fruiting bodies have a structure of a haystack and have a core filled with spherical spores formed from the cells

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11
Q

what are fruiting bodies an example of in bacteria?

A

complex bacterial pattern formation:
- fruiting bodies can be very complicated and their appearance is species specific
- bacteria can make structures in the millimetre range, despite being micrometres in size themselves
- this is due to an elaborate plan to form these specific structures

could be used to help understand complex pattern formation in eukaryotes e.g. organ development

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12
Q

what 3 distinct cell fates does Myxobacterial differentiation from a fruiting body result in?

A
  1. autolysis - 80% of cells
  2. differentiation into spores - 15% of cells
  3. differentiation into peripheral rods - 5% of cells
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13
Q

what is autolysis of Myxobacteria when differentiating to a fruiting body?

A
  • 80% of the cells undergo autolysis to liberate nutrients
  • this allows the other cells to differentiate into spores to successfully complete their own differentiation
  • known as an altruistic behaviour
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14
Q

when differentiating from a fruiting body, what do 15% of the Myxobacterial cells differentiate to?

A
  • 15% of cells differentiate into spores
  • spores are highly resistant to heat, desiccation, radiation etc
  • they develop a thick carbohydrate spore coat
  • they possess a 2N genome, as their first cell division doesn’t require energy to double their chromosomes as they are already diploid
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15
Q

when differentiating from a fruiting body, what do 5% of the Myxobacterial cells differentiate to?

A
  • 5% of cells differentiate into peripheral rods
  • peripheral rods are cells that stay vegetative but hardly divide
  • they are interpreted as scout cells that can quickly initiate swarm development when the population encounters nutrients again
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16
Q

how can fruiting bodies be transported?

A

Small animals like rats can transport fruiting bodies, so when spores germinate they can start out as a swarm

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17
Q

How do fruiting bodies develop?

A
  • fruiting body formation begins via aggregation - occurs when cells bump into each other and clump due to cell density
  • after initial aggregation, more cells stream into the structure and swirl around to form a fruiting body mound
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18
Q

What triggers Myxobacteria to differentiate?

A

The C-signal

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19
Q

what is the C-signal (2 theories)?

A
  1. the short cleaved C-terminal fragment of CsgA is the C-signal
  2. DAG is the C-signal
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20
Q

what is the CgsA theory of the C-signal?

A
  • C-signalling is completed by a fragment of CgsA (part of the biochemical family called Short Chain Alcohol Dehydrogenases)
  • the CgsA protein is cleaved into a shorter C-terminal fragment
  • it is the C-terminal fragment which is thought to be the C-signal, as it interacts with a receptor on another cell to stimulate the alignment of the 2 cells
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21
Q

what is the limitation of the CgsA theory on C-signals?

A

Myxococcus has another Short Chain Alcohol Dehydrogenase called SocA:
- SocA is from an amino acid sequence that lacks homology in the C-terminal of CsgA
- when CsgA is deleted, the cell no longer forms fruiting bodies
- however, when SocA is overexpressed, the cell can start making fruiting bodies again
- therefore SocA can replace the C-signal, as it produces a similar enzyme to CsgA

therefore the C-terminal fragment of CgsA may not be the sole C-signal

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22
Q

what is the DAG theory of C-signal?

A

CsgA from Myxococcus and HSD10 from humans are cardiolipin phospholipases that produce, through oxidation, diacyglycerol (DAG)
- evidence: a DAG-containing lipid can initiate Myxobacterial developmental differentiation in an M. xanthus that has a CsgA mutation/knockout

therefore DAG is the C-signal

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23
Q

how do Myxobacteria recognise kin?

A

Via outer membrane exchange between cells:
- Myxobacteria can transfer outer membrane proteins and lipids between 2 adjacent cells
- this involves fusion of the outer membrane
- this can only occur is the 2 cells express similar alleles of a cell surface protein called TraA, which has a specific N-terminus

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24
Q

what is TraA and what is its role in kin recognition/outer membrane exchange?

A

TraA is a recognition protein that interacts with a carbohydrate glycan receptor on adjacent cells
- it enables communication between kin and non-kin cells
- if it recognises a kin cell, it enables fruiting body formation
- one cell can fuse its membrane with another cell to exchange cellular content, allowing cells to repair damage to neighbouring cells

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25
Q

what is the Kin system in Myxobacteria?

A
  • heterogenous cells expressing different TraA alleles (different N-terminus) do not exchange outer membrane components, so cannot form fruiting bodies
  • this phenomenon ensures kin recognition of cells of the same species/strain, where many myxobacterial species/strains may co-exist
  • only cells which are genetically cloned/similar can share cellular contents
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26
Q

what are Cyanobacteria?

A
  • a large, diverse group of photosynthetic prokaryotes
  • found in oceans, lakes and soil
  • gram-negative photoautotrophs - can fix CO2 in the Calvin cycle
  • show gliding motility via type IV pili (retractable cell appendages for swarming)
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27
Q

how do filamentous cyanobacteria move?

A

they use alpha-motility

28
Q

how do marine cyanobacteria move?

A

they swim but without a cell appendage/flagellum

29
Q

how are Cyanobacteria polymorphic?

A
  • Some groups of Cyanobacteria show complex differentiation and polymorphic cell-cycles which are nutritionally controlled, most importantly by the availability of nitrogen
  • Lack of a source of ‘fixed’ nitrogen (e.g. ammonium ions NH4+) results in the formation of specialised cells called heterocysts to convert (fix) atmospheric nitrogen to ammonium ions
30
Q

what are the major groups of Cyanobacteria, from simple to complex?

A
  1. Chroococcacean
  2. Pleurocapsalean
  3. Oscillatorian
  4. Heterocystous
31
Q

what are the characteristics of the Chroococcacean group of Cyanobacteria?

A
  • unicellular rods or cocci
  • non-motile
  • divide by binary fission
  • can have up to 4 cells in one sheet
  • the sheets eventually break apart for binary fission
32
Q

what are the characteristics of the Pleurocapsalean group of Cyanobacteria?

A
  • unicellular but form cell aggregates
  • unique mode of cell division by multiple fission of a vegetative cell to form Baeocytes
  • Baeocytes are spore-like entities which are resting cells
33
Q

what are the characteristics of the Oscillatorian group of Cyanobacteria?

A
  • the most common form of Cyanobacteria
  • multicellular
  • individual cells form filaments called Trichomes
  • move by gliding
  • filaments can break up into motile units called Hormogonia
34
Q

what are the characteristics of the Heterocystous group of Cyanobacteria?

A
  • Heterocysts are large and have a thick cell wall
  • individual cells form Trichome filaments which contain the heterocysts
  • they can produce resting cells inside the filament called Akinetes
  • they also produce the Hormogonia motile units
35
Q

how do heterocysts form?

A

They form regularly along the filament:
- When filament grows, cell division occurs within the filament
- When two akinetes form, they extend the filament, and exactly in the middle of the 2 akinetes, another division occurs which produces a heterocyst
- Results in regular intervals of heterocysts

36
Q

what are the properties of heterocysts?

A
  • they are terminally differentiated cells which cannot divide once formed - they have a finite life span
  • they have no Calvin cycle so cannot fix CO2
  • they fix atmospheric nitrogen using nitrogenase, an oxygen-sensitive enzyme
37
Q

Cyanobacteria perform oxygenic photosynthesis, so how can nitrogenase function in heterocysts if it cannot function in presence of oxygen?

A

Heterocysts contain low content of photosynthetic membranes and only photosystem 1 (no oxygen generation)
- Thick outer envelope layers: thought to restrict diffusion of oxygen into cell which might damage nitrogenase

38
Q

what are the metabolic differences between vegetative cells and heterocysts?

A
  • Vegetative cell contains PSI and PSII, where PSII is oxygenic
  • In heterocyst, only PSI is present and it uses ETC to generate PMF and nitrogenase that reduces nitrogen to ammonium, which is distributed to neighbouring cells
39
Q

how is heterocyst develpoment genetically regulated?

A
  1. Early events regulated by NtcA, a regulatory protein which monitors nitrogen status of the cell by binding to low ammonium
  2. NtcA controls HetR, a DNA binding protein which aids transcription at het gene promoters
    - Genes needed for correct spacing of heterocysts
    - Genes encoding envelope polysaccharides which help keep out oxygen
  3. when HetR is activated, it activates het promoter which enables transcription of the het gene and heterocyst formation
40
Q

how are anabaena filaments regulated?

A
  • When grown in nitrogen-containing medium, it forms vegetative cells
  • When in low nitrogen conditions, they develop heterocysts which become fully mature after 24 hours
  • Forms regular intervals due to cells constantly dividing
41
Q

what is the process of gene regulation in heterocyst development?

A
  1. Nitrogen deficiency/low ammonium is sensed by NtcA as an increase in cytoplasmic 2-oxoglutarate:ammonium ratio
  2. NtcA activates HetR, and the 2 increase expression of HetF
    - HetR triggers heterocyst formation
  3. HetF interacts with HetR to trigger positive feedback loop, causing amplified HetR and NtcA signalling (auto-upregulation)
  4. PatS peptide binds and inactivates HetR to stop signalling and heterocyst formation
  5. HetN is a large, non-diffusible protein only found in the heterocyst, and HetR and PatS bind to HetN, lowering amount of free-PatS in the heterocyst to continue to develop, as PatS no longer sequesters HetR
  6. PatS can diffuse into neighbouring cells to prevent them from differentiating to heterocysts
  7. a thick-walled nitrogen-fixing heterocyst is formed that imports carbon compounds from neighbouring vegetative cells and exports ammonium
    - this allows the heterocyst to continus
42
Q

what is the initial response bacteria undertake to deal with nutrient stress?

A
  • the initial response is often the stringent response alarmone ppGpp and ppGppp
  • this leads to subsequent activation of regulons that increase nutrient uptake, transcribe chaperons and reprogramme the metabolism
43
Q

what is an effective strategy some bacteria use to deal with severe stress?

A

Formation of resting cells such as spores and cysts: sporulation
- these cells are metabolically dormant and possess increased resistance against physical and chemical stress
- spores are more resistant to high temperatures than vegetative cells

44
Q

is sporulation the go-to method for bacteria when dealing with stress?

A

no, sporulation is the last resort as it is an irreversible process
- when undergoing sporulation, the cell cannot become a vegetative cell at any point during the process
- it must wait until germination to become a vegetative cell again

therefore, the cell must prolong/delay the decision of undertaking sporulation

45
Q

what different resting cells can bacteria form?

A
  • Most common is endospores e.g. from Bacillus
  • Aerial spore from streptomyces – normally they grow as mycelium, but has to change growth models and cell wall to merge from water to air and become spores
  • Zoospores have flagellum so can spread
  • Small dense cells and elementary bodies are more exotic and are resistant to external stresses
  • Akinetes are resting cells
46
Q

what is the ultrastructure of the Bacillus endospore?

A
  • has a spore cortex composed of peptidoglycan
  • inner and outer spore coats surround the spore core
  • the core contains a compacted chromosome
  • the core is very small, and the layers/coats surrounding it are very thick, enabling their resistance to stresses
  • multi-layer wall is composed of protein and carbohydrate
  • cytoplasm is condensed and dehydrated
  • core contains 5-15% dry-weight dipicolinic acid (DPA)
47
Q

what is DPA and its function in the Bacillus endospore core?

A

DPA protects the DNA via intercalation to compact the DNA, making it more resistant to chemical and physical attrition

48
Q

is DPA the sole DNA protector of the Bacillus endospore?

A

In mutants that don’t produce DPA, the spores are still resistant to heat and chemicals, so maybe DPA isn’t the sole resistor and there are other resistance factors.

49
Q

what is the role of DPA in food technology?

A

In food technology and environmental sciences, DPA is used in an assay with terbium to detect the presence of spores. Chemically, the molecule is a biodegradable pyridine.

50
Q

what triggers sporulation in bacteria?

A

cell stress/starvation

51
Q

what are the main adaptations of the Bacillus endospore

A
  1. dehydrated core due to DPA - allows heat and radiation resistance
  2. small acid-soluble proteins (SASPs) - protect DNA from heat, chemicals and radiation
    - 3 major SASPs: alpha, beta, gamma - when one SASP is removed, the other 2 are upregulated
  3. Ca(II)DPA - stabilises DNA
  4. Coat - resistance to organic solvents, chemicals
52
Q

what is the process of endospore formation (sporulation) in Bacillus subtilis?

A
  1. DNA replication + chromosome segregation occurs in axial filament
  2. asymmetric septum develops at one pole, forming larger mother cell and small forespore
  3. Spore-3E protein ensures DNA is pumped into forespore across the axial filament, and that chromosomes are fully segregated
  4. Large mother cell engulfs the forespore, so 2 membranes surround the spore cell
  5. cortex formation begins when cell synthesises peptidoglycan and installs a new cell wall between the 2 membranes
    -DPA and SASPs are formed, coat proteins laid and exosporangion is formed
  6. mother cell chromosomes are degraded
  7. peptidoglycan outer layer is broken down and recycled
  8. spore is released where it is dormant until conditions are reached where it can germinate
53
Q

when the spore is formed, what 2 fates may it take?

A
  1. it can germinate and repeat the sporulation process
  2. it can germinate and enter vegetative growth by binary fission
    - all compounds are recycled for the formation of a vegetative cell
54
Q

what factors genetically regulate sporulation?

A
  • sigma factors determine the affinity of RNAP to specific promoters and control different regulons
  • 100 genes are involved in sporulation
  • 4 main sigma factors are crucial for sporulation and exist in pairs
  • criss-cross interaction between the sigma factors maintains the precise timing of the process
55
Q

what are the 4 main sigma factors involved in sporulation and what are the pairs?

A
  1. Sigma-F and sigma-G exist in the forespore
  2. Sigma-E and sigma-K exist in the mother cell
56
Q

what is the process of sigma factor regulation in Bacillus endospore formation?

A
  1. SpoOA is a master regulator of sporulation and initiates sporulation when it detects low nutrients
  2. SpoOA expression is controlled by sigma-H -> conc of SpoOA increases 7-fold under low nutrients to drive sporulation
  3. increased SpoOA activates sigma-F, which is accumulated in forespore, but some in mother cell
    - high amounts of F and E in forespore and mother respectively, but importantly there are some small amounts of F in mother and E in forespore
  4. sigma-E and sigma-K are initially inactive pro-sigma factors
    - sigma-F via triggers a protease which converts pro-E to an active state
  5. sigma-E controls sigma-G formation in the forespore
  6. Sigma-G activates a protease which converts pro-K to sigma-K in the mother cell
    - sigma-G and sigma-K do not mix and stay exclusively in their compartments, unlike F and E
57
Q

why is the sigma factor cascade in sporulation so important?

A

Cascade ensures that each step of process is in a strict sequence:
- Sigma factor at initial step is needed to make the next sigma factor and next gene expression of the development
- Pro-sigma-factors ensures that E and K do not prematurely start gene transcription
- F and G are needed first for protease function before E and K can begin transcription

58
Q

what are the characteristics of a Myxococcus xanthus fruiting body?

A
  • Spores are found in sporangioles within the fruiting bodies
  • Animals may pick up the sporangiole and the spores start out already as a swarm
  • Mass that makes the fruiting body is dead/remnant cellular material
  • During process of formation, cells actively move around in fruiting body before arresting in the sporangiole
  • Uppermost layer of cells in fruiting body do not form spores but stay vegetative to generate carbohydrate blanket which surrounds the structure - kinship
59
Q

what are the characteristics of a Stigmatella aurantiacia fruiting body?

A
  • Has unique feature where fruiting body formation is triggered by light
  • Stigmalone can override nutrient existence to continue to form fruiting bodies
60
Q

how do endospores form inside the fruiting body?

A

During the formation of endospores (i.e. Bacillus species) the cell undergoes an unequal division resulting in a mother cell and the prespore cell.
- Spore formation occurs in mother cell
- Spore has 2x n chromosomes, so there is cell division and chromosome segregation
- More energy expenditure
- Peptidoglycan formation is already in correct shape -> keeps peptidoglycan for protective layer

61
Q

how do myxospores form inside the fruiting body?

A

During the formation of myxospores (i.e. Myxococcus species) the entire cell will become spherical and turn into a spore.
- Entire rod cell converts into one spherical spore
- No cell division is needed and keeps 2N genome
- More energy efficient as no chromosome duplication needed
- 2 copies of chromosomes so cell more likely to survive if one set gets damaged
- Has to remove peptidoglycan to change from rod to spherical spore -removes mechanical barrier and stabiliser of spore cell wall -> spore is more vulnerable to osmotic changes

62
Q

what are MDOs and OPGs?

A
  1. MDOs are membrane-derived oligosaccharides - found in E.coli
    -E. coli recycles LPS into MDO which exist in periplasm and are important in regulating osmotic stresses
  2. OPGs are osmo-regulated periplasmic glucan - found in Gram-negative
    - similar function to MDOs
    - constrained to the periplasm
63
Q

how is sporulation protected in myxococcus bacteria?

A

There fibre-large polysaccharides made from 4 different sugars and function in protecting the conversion to spore

64
Q

what are glycerol spores?

A

Glycerol spores are spore-like entities that are formed by Myxococcus cells in response to substances such as glycerol that interfere with cell growth
- They are similar but also different from fruiting body spores
- They are not true spores and are less resistant to stresses

65
Q

what is the structure of a fruiting body myxospore?

A
  • Have thinner layers which become much thicker with massive carbohydrate structure for mechanical resistance
  • DNA condensed by 96hrs
  • Lipids are used for energy to convert excess membrane from rod shape to spore shape
  • Lipid droplets are one of first step to commit to sporulation
66
Q

what is the structure of a glycerol spore?

A
  • Lack formation of lipid droplets
  • Lack carbohydrate cell wall structure
  • Have proteins in cell wall so make them more resistant then vegetative cells, but less than normal spores

Microbiology 2 (10 decks)

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