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Microbiology II > Topic 3 - Bacterial cell differentiation > Flashcards

Topic 3 - Bacterial cell differentiation Flashcards

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1
Q

Bacterial Development results in cells having
one of four basic Functions

A

Stress survival
Physiological specialisation
Cell dispersal
Symbiotic relationship

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2
Q

what is Myxococcus xanthus a model organism for

A

developmental differentiation
kinship + altruism + cooperation
type IV pili
bacterial motor systems
prokaryotic signalling

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3
Q

what is encoded in Myxococcus xanthus’ large chromosome

A

10Mb genome
200 TCS
181 transcriptional regulators
43 sigma factors

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4
Q

Differences between Myxococcus xanthus and E. Coli

A

more sigma factors - can respond to more things
kinship - can coordinate behaviour across a whole population

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5
Q

what does starvation lead to in Myxococcus xanthus

A

initiates the differentiation pathway to form a fruiting body waits till it cannot be avoided as it is reversible

starvation is detected –> ppGpp, A signalling
C signals co-ordinate the building of the fruiting body

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6
Q

what are fruiting bodies made up of

A

cells that have undergone autolysis

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7
Q

what are the 3 cell fates of Myxococcus xanthus differentiation

A

80% - autolysis, liberate nutrients
15% - spores, thick carbohydrate coat and 2N genome
5% - peripheral rods

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8
Q

C signals

A

Contact dependent signals responsible for fruiting bodies through CsgA a short chain alcohol dehydrogenase
contact dependant “signal”
produces diacylglycerol (DAG) which diffuses (the c signal) OR other theory the protein is made into smaller signal by protease and displayed on the cell surface (C signal)

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9
Q

what is the point of kin recognition

A

to stop other bacteria using the cells to form its own spores

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10
Q

kin recognition proteins? what happens?

A

TraA = recognition protein
Glycan = receptor
specific to species - the two cells must express similar alleles of TraA
when bound outer membranes may fuse share lipids etc.

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11
Q

what is A-signalling

A

aromatic amino acids initial factor in starvation response as they are costly to make

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12
Q

What is physiological Specialisation?

A

The formation/occurrence of cells with distinct and complimentary physiological features (e.g. myxobacteria fruiting bodies and cyanobacteria heterocysts)

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13
Q

What is Stress Survival?

A

The conversion/ gene switching of cells into a less metabolically active form with high resistance and don’t divide (e.g Bacillus endospores)

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14
Q

what is cell dispersal

A

motility eg. flagella, surface associated motility, or passive motility by wind, water, or animals

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15
Q

what is myxococcus xanthus a model organism for

A

they show developmental differentiation, kinship, altruism and cooperation, type IV pili, horizontal gene transfer and prokaryotic signalling processes

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16
Q

what is a difference between myxococcus xanthus and e. coli and what does this allow

A

M xanthus has more sigma factors and can therefore respond to more things and coordinate behaviour across a population

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17
Q

what are the three distinct fates of myxobacteria with results and %

A

autolysis (to liberate nutrients) 80%
spores (resistance to heat, desiccation and radiation) 15%
peripheral rods (“scout cells”) 5%

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18
Q

what are peripheral rod cells

A

stay vegetative but hardly divide
“scout cells” can initiate swarm development when they encounter nutrients

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19
Q

how do populations orchestrate cell movements (form chain)

A

C-signal (technically not a signal, it is Contact dpenedant)

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20
Q

what is kin recognition, what is required for it to occur

A

in myxobacteria, ability to transfer outer membrane proteins and lipids, involves fusion of the outer membrane
only occurs if the the cells express a similar allele of a cell surface protein called TraA

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21
Q

where are myxobacteria found

A

the soil

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22
Q

what are cyanobacteria

A
  • diverse group of photosynthetic prokaryotes, found in oceans, lakes and soil
  • Gram-negative photoautotrophs (fix CO2 in the Calvin cycle)
  • Often show gliding motility (none have flagella)
  • Lack of a source of “fixed” nitrogen (e.g. ammonium ions NH4+) results in the formation of specialised cells (heterocysts) to convert (“fix”) atmospheric N2 to ammonium ions.
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23
Q

what is ppGpp what can it activate

A

an intracellular stress response (pheromone - alarmone) which also regulates sporulation
activates regulon –> increase nutrient uptake, transcribe chaperones, reprogram metabolism

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24
Q

describe the ultrastructure of a bacillus endospore, what is its purpose

A

multiple layers of peptidoglycan - thick cortex - resistant to organic solvents and chemicals
dehydrated core - heat and radiation resistant
looses some things to protect DNA - this is the purpose of spores

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25
Q

how is DNA stabilised in a bacillus endospore

A

dipicolinic acid (DPA) (normally as Ca2+ DPA complex)

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26
Q

what is the difference between endosporulation and myxosporylation

A

in endospores the division is unequal with one mother cell and prespore cell, in myxospores the entire cell will become spherical and turn into a spore

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27
Q

structure of a bacillus endospore

A

outer coat, inner coat, cortex, core, nucleoid

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28
Q

instructions for diagram of endospore formation

A

cell can go to vegetative growth or sporulation
1. axial filament - inner membrane goes in a bit on one side (DNA pump is ensuring DNA is correctly separated)
2. membrane septum forms - mother cell, forespore
3. engulfment
4. cortex forms (mother chromosome is degraded)
5. exosporangium forms (Ca(II) DPA synthesis)
6. spore coat formed
7. spore is released

can germinate back to vegetative cell

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29
Q

what features make spores (bacillus endospore) resistant to chemical and physical stress

A

the hydrated core is resistant to heat and radiation stress
SASPs small acid soluble proteins protect DNA from heat chemicals and radiation
as does the Ca2+DPA which makes up 5-15% dry weight of the nucleoid (forms crystals)
the coat of the spore is resistant to organic solvents due to its low permeability

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30
Q

what signals lead to the formation of spores (+ differentiation)

A

A signals and unloaded tRNA - starvation
this activates the stringent response - alarmones ppGpp and ppGppp this leads to formation of resting cells such as spores

differentiation
C signal collect cells together contact dependent
Kin recognition using TraA and TraB proteins only share lipid with cells with the same alleles in TraA/TraB

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31
Q

sigma F

A

early stages of Forespore development

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32
Q

sigma E

A

Engulfment of forespore, as well as genes necessary for the later stages of spore coat formation and mother cell lysis

33
Q

sigma G

A

post-enGulfment maturation of forespore, cortex, coat, resistance properties

34
Q

sigma K

A

final stages of spore coat formation + lysis of the mother cell
(lysis - think lysine (K))

35
Q

Comparison of endo- and myxospore formation

A

during the formation of endospores the cell undergoes an unequal division resulting in a mother cell and the forespore cell

During the formation of myxospores the entire cell will become spherical and turn into a spore (chromosome replication still occurs - giving first cell division for free)

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

36
Q

Provide examples of symbiotic relationships between bacteria and other organisms:

A
  • Rhizobium nodulation in plants (for nitrogen fixing in legume for cell growth in less fertile soils)
  • Vibrio fisheri -> live in the light organs of a squid species, providing bioluminescence to attract prey.
37
Q

What features is myxococcus xanthus used to study?

A

Biolfilm formation, developmental differentiation, autolysis, kinship differentiation, altruism, cooperation, bacterial motor systems, biological pest control,

38
Q

What is the bacterial motor mechanism of Myxococcus xanthus?

A

they adopt different forms of motility in different environments, however their most interesting is the synchronous secretion of slime to propel the cell.

39
Q

What does the LUCA acronym mean?

A

Last universal common ancestor -> the cell which had the essential parts for all life.

40
Q

What is the life cycle of myxococcus xanthus?

A

Cells in vegetative state change behaviour in depletion of nutrient supply (via A signalling) -> swarm inwards to form mounds which develop into fruiting bodies (via C signalling) -> these spores will spread by wind or contact with animals, later germinating in more favourable conditions.

41
Q

How is myxococcus xanthus an example of altruism?

A

85% of cells will undergo autolysis to provide nutrients to other cells for formation during fruiting body / mound formation.

42
Q

What is diacylglycerol?

A

A diffusible signal used in the diffusion of C signals.

43
Q

What occurs between cells which share TraA/TraB alleles?

A

Kinship occurs, exchanging outer membrane components and forming fruiting bodies.

44
Q

What is an example of a fast growing cyanobacteria which is responsible for 50% of global nitrogen fixation:

A

Trichodesmium

45
Q

What nutrients are required by cyanobacteria?

A

Nitrogen, Phosphates, and other micronutrients.

46
Q

What are the properties of undruggable proteins?

A

Proteins which have no easy cleft which a small molecule could bind to disrupt function -> cyanobactins can be used

47
Q

What are the major groups of cyanobacteria?

A

Chroococcacean
Pleurocapsalean
Oscillatorian
Heterocystous

48
Q

Chroococcacean Cyanobacteria:

A

Non-motile unicellular rods or cocci that divide by binary fission

49
Q

Pleurocasalean:

A

Unicellular cocci which form aggregate; have a unique mode of cell-division only undergoing multiple fission of vegetative cells to form baeocytes.

50
Q

Oscillatorian:

A

Trichomes (filaments formed by cells) break up into motile units of a few cell called hormgonia

51
Q

Heterocystous:

A

Forms cell filaments of trichomes, containing heterocysts which produce resting akinetes and hormogonia.

52
Q

What are the properties of heterocysts:

A

They’re terminally differentiated and cannot divide once formed -> lack a Calvin cycle and can’t fix CO2 -> fix atmospheric nitrogen to ammonium using nitrogenase -> Cell wall impermeable to oxygen (growing thicker than vegetative) -> low content of photosynthetic membranes to limit O2 production and continue nitrogen fixation.

53
Q

What amino acid residues are used for ammonia transport?

A

Glutamate and Glutamine.

54
Q

What is different between the PSI and PSII relationship with the ETC?

A

PSI is donates an electron to the ETC and is regenerated by the ETC, whereas PSII donates an electron to the ETC but is not regenerated by it (instead by H2O to form O2)

55
Q

Genetic Regulation of Heterocyst development:

A

Heterocysts form at regular intervals across the trichome; their differentiation from vegetative cells is determined by the NtcA regulatory protein, that in response to low NH4+ (ammonium) caused by trichome extension with the cell’s distance from the Heterocyst NH4+ source increasing, will aid in the transcription of the het gene by HetR regulation which will trigger differentiation.

56
Q

How is the differentiation of cells neighbouring Heterocysts prevented?

A

PatS and HetN are diffusible peptide signals secreted by Heterocysts that prevents neighbouring vegetative cell differentiation.

57
Q

If heterocysts don’t use the Calvin Cycle, how do they source carbon compounds?

A

Their carbon compounds are imported from the vegetative cells.

58
Q

How are ammonium levels detected in cyanobacteria?

A

The levels of glutamine, low glutamine levels => low NH4+, and the opposite is true -> high glutamine levels => high Nh4+

59
Q

What is endosporulation:

A

The process of the cell undergoing unequal division resulting in a mother cell and a pre-spore cell.

60
Q

What are OPGs?

A

Osmo-regulate periplasmic glucans -> membrane derived oligosaccharides

61
Q

Difference between glycerol and fruiting body spores? (Against mechanical force)

A

Glycerol spores are less stable than fruiting body spores.

62
Q

What is Bdellovibrio?

A

Bdellovibrio is a fast-swimming predatory gram-negative bacteria -> attaching to the outside of prey cells, using an enzyme hydrolysis drill mechanism within which it’s inserted into the periplasm-> the Bdellovibrio then breaks down the IM and the prey’s cytoplasmic components, replicating inside the OM via filamentous growth. Lysis of the OM occurs and the progeny are released.

63
Q

What is the mechanism of DNA replication:

A

DnaA-ATP binds at the oriC, causing the recruitment of components of the membrane-bound replisome. DnaB helicase unwinds the DNA to form a replication fork. In E.coli DNA polymerase 3 (Pol III) coupled to the ring-shaped clamp loader catalyses the DNA synthesis of the leading strand. The lagging strand is synthesised as short okazaki fragments of DNA primers by primase DnaG, each requiring the loading of a beta-clamp .

64
Q

What protects the lagging strand in DNA replication?

A

A single-stranded DNA-binding (SSB) protein

65
Q

What form of DnaA is active for DNA replication?

A

DnaA-ATP

66
Q

What inhibits DNaA activation?

A

SeqA (during the eclipse period)

67
Q

What occurs during the “eclipse” period of DNA replication initiation?

A

“old” DnaA-ATP becomes “new” DnaA-ADP

68
Q

What ratio of DnaA-ATP ; DnaA-ADP initiates replication?

A

1:1

69
Q

What is the sizer mechanism:

A

Cells grow to an average size regardless of their birth size and then divide

70
Q

What is the adder mechanism:

A

Cells add a constant size between birth and division, independent of their birth size.

71
Q

Is the add or sizer mechanism favoured as an explanation for cell size upon cell division?

A

The adder mechanism, being observed in several bacteria, but also single celled eukaryotes (yeast) and archeae

72
Q

Mechanism of DNA replication Control:

A

The process is mainly controlled by two processes:
1) The concentration of the enzyme ribonucleotide reductase (RNR) that synthesises dNTP (free DNA nucleotides) and is encoded by the nrdAB (regulated at a transcriptional level by the overall concentration of DnaA-ATP. NrdR (TF) can act as a repressor of the operon.
2) The inhibition of primase DnaG (when nutrients are low inside the cell) during stringent response. ppGpp and ppGppp will inhibit the primase.

73
Q

What are the methods of division site selection:

A

1) SlmA nucleoid occlusion: depolymerisation or capture
2) MinCDE function as an oscillating geometric positioning system
3) Ter Linkage: TerDNA specifically base pairs across the chromosome -> binding protein complexes (unknown mechanistic function)
4) DNA translocase FtsK positions the ter region dif site in the divisome in late stage division.

74
Q

What are the roles of FtsZ?

A
  • FtsZ forms a filamentous ring (similar to tubulin rings), which slide across each other to constrict the FtsZ ring during constriction.
  • incubates liposomes with FtsZ and FtsA (element) , leading to the formation of protofilaments leading to bending of the OM/ invagination.
75
Q

Why is the constriction of FtsZ not enough for the invagination of cell membrane and peptidoglycan?

A

The constriction action doesn’t have enough energy, requiring the aid of liposomes.

76
Q

Describe the MinCDE system of E.coli division control:

A

The MinCDE system is a negative regulation system: MinC is a division inhibitor (inhibiting FtsZ) which associates and co-oscillates with MinD. Their pole-to-pole oscillation in turn requiring activity of MinE ring.

77
Q

What protein positions the ter region?

A

FtsK as a DNA translocase.

78
Q

What is would be a positive regulation system of cell division site determination?

A

Proteins will mark the region where division will occur. (e.g. SsgA marks Streptomyces coelicor future division sites and recruits FtsZ)

Microbiology II (8 decks)

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