Bacterial Cell Differentiation

Question 1

What are the 4 categories for how bacteria cells can adapt to the environment?

Answer 1

1. Stress survival:
   >Conversion of cells into resting cells with low metabolic activity and high resistance to stress (e.g. Bacillus endospores).
2. Physiological specialization:
   >Occurrence and formation of cells that possess physiological features complementary to the normal vegetative cells (e.g. myxobacterial fruiting bodies, cyanobacteria heterocysts).
3. Cell dispersal:
   >Production of cells that either actively use flagella or surface-associated motility or passively by wind, water or animals (e.g. Caulobacter swarmer cells).
4. Symbiotic relationship:
   >Interaction with other cells can lead to the establishment of a symbiotic relationship (e.g. Rhizobium nodulation).

Question 2

What are Myxobacteria known for?

Answer 2

A group of gram-negative bacteria that are characterized by their complex social behaviour and ability to form multicellular structures

Question 3

What is Myxococcus xanthus?

Answer 3

A Myxobacteria apart of the Proteobacteria class

Question 4

What features define Myxococcus xanthus in the proteobacteria class?

Answer 4

Complex-life-style, social behaviours and large genomes

Question 5

What are 4 defining characteristics of myxobacteria?

Answer 5

1. Gliding motility:
   >Myxobacteria are able to move across surfaces using a type of motility called gliding. Unlike many other bacteria that move using flagella, myxobacteria do not have flagella and instead use other mechanisms to propel themselves along surfaces.
2. Social behaviour:
   >Myxobacteria are known for their complex social behaviour, which includes the ability to communicate with one another using chemical signals, coordinate their movements and behaviours, and form multicellular structures.
3. Fruiting body formation:
   >Myxobacteria are able to form multicellular structures called fruiting bodies, which are composed of groups of cells that differentiate into specialized cell types. Fruiting bodies are thought to help myxobacteria survive in harsh environments by allowing them to form spores that can withstand adverse conditions.
4. Metabolic diversity:
   >Myxobacteria are able to use a wide range of metabolic pathways to obtain energy, including aerobic and anaerobic respiration, fermentation, and chemosynthesis.

Question 6

What are the 3 cell fates during development differentiation in Myxococcus xanthus while forming fruiting bodies?

Answer 6

1. 80% of cell undergo autolysis to form Non-motile spherical cells
   >Autolysis liberates nutrients so some of these cells can eventually differentiate into spores.
2. 15% of cells differentiate into spores
   >Myxospores: dormant, highly resistant cells that are formed from the non-motile spherical cells within the fruiting body. Myxospores are highly resistant to environmental stresses, such as desiccation and UV radiation, and can remain viable for long periods of time. When environmental conditions become favourable, myxospores can germinate and give rise to new vegetative cells.
3. 5% of cells differentiate into rod-shaped motile cells
   >Cells that stay vegetative but hardly divide. They are usually interpreted as “scout cells” that can quickly initiate swarm develop (quick germination) when the cells encounter nutrients.

Question 7

Describe the C-signaling hypothesis for fruiting body formation in Myxococcus xanthus in 5 steps

Answer 7

1: Nutrient depletion leads to the production of A-signal, which triggers cell aggregation to form mounds.

2: As cells aggregate, they start producing CsgA protein.

3: CsgA is then processed by proteases to release a short C-terminal peptide, called C-signal.

4: The C-signal sticks out through the surface of the cell membrane and interacts with other cells in the mound, causing cells to align themselves.

5: The aligned cells then differentiate into either: non-motile spherical cells, spores, rod-shaped motile cells (mature into fruiting bodies).

Question 8

Describe the DAG hypothesis for fruiting body formation in Myxococcus xanthus in 5 steps

Answer 8

1: Nutrient depletion leads to the production of A-signal, which triggers cell aggregation to form mounds.

2: As cells aggregate, they start producing CsgA and SocA enzymes.

3: CsgA and SocA oxidize DAG (1,2-diacylglycerol) to produce a chemical signal, or C-signal.

4: The C-signal then interacts with other cells in the mound, causing cells to align themselves.

5: The aligned cells then differentiate into either: non-motile spherical cells, spores, rod-shaped motile cells (mature into fruiting bodies)

Question 9

What state are Myxococcus xanthus found in in nutrient rich environments?

Answer 9

Cells glide move around soil via gliding motility as a swarm and hunt for bacterial prey.

Question 10

How do Myxobacteria prevent formation of fruiting bodies with other species and ensure that other species of Myxobacteria don’t enter their fruiting body and steal nutrients?

Answer 10

By Kin recognition

Question 11

How do Myxococcus xanthus establish Kin recognition?

Answer 11

By TraA recognition system:

> TraA is a recognition protein that interacts with a carbohydrate (glycan) receptor on the adjacent cells
There is high difference of the TraA sequence in Myxobacteria of different species, this means this protein can act as a recognition site for Myxobacteria to recognise that of their own species; as only a TraA from their species can bind with a glycan receptor from the same species. If the interaction shows they are kin, the cells form a fruiting body

Question 12

What interaction can occur if Myxobacteria establish Kin relationship?

Answer 12

> Can have temporally fusion of outer membranes with neighbouring Myxobacteria to allow exchange of cellular content (allows cells to repair damaged neighbouring cells)

> This ONLY occurs, however, if the two cells express similar alleles of a cell surface protein called TraA. (have to be from the same species)

Question 13

What are Cyanobacteria?

Answer 13

> Also known as blue-green algae, are a diverse group of photosynthetic prokaryotes found in oceans, lakes and soil.

> Gram-negative photoautotrophs (fix CO2 in the Calvin cycle)

Question 14

What specialised cell types make up the filamentous cyanobacteria Anabaena and their roles?

Answer 14

1. Heterocysts
   > Heterocysts are specialized cells that are involved in nitrogen fixation, a process that converts atmospheric nitrogen into a form that can be used by the cell.
2. Akinetes

Question 15

Describe the overall structure of a filamentous cyanobacteria?

Answer 15

Although filamentous cyanobacteria are multicellular, each individual cell in the filament is still unicellular. Different cells may specialize to perform different functions, such as nitrogen fixation or spore formation.

Question 16

What does Trichome mean?

Answer 16

Trichomes are the long chains of cells that form the filamentous structure of the cyanobacteria

Question 17

Name three distinct cell types of filamentous cyanobacteria and describe their functions

Answer 17

1. Heterocysts (phyiological specialized cells to help resting cells) (low nitrogen conc).
   > Heterocysts are specialized cells that are responsible for nitrogen fixation in filamentous cyanobacteria.
2. Akinetes (resting cells)
   > Large, dormant cells that form in response to adverse environmental conditions such as nutrient limitation desiccation. Are able to withstand these harsh conditions because they have thick cell walls and can store nutrients for later use
3. hormogonia filaments
   >Motile filaments

> Vegetative cells are found when no stress is present.
Carry out most of the metabolic processes required for growth and reproduction. Vegetative cells are responsible for carrying out oxygenic photosynthesis, which produces oxygen and organic compounds that can be used for energy and growth. They are also able to differentiate into heterocysts or akinetes in response to environmental cues.

Question 18

How can Heterocyst cells carry out nitrogen fixation in Anabaena?

Answer 18

Because they lack photosystem II, which is required for oxygenic photosynthesis. As only have photosystem I and have nitrogenise (active when no O2 is present) can fix nitrogen to ammonia.

Question 19

What is the state of a filamentous cyanobacteria when a) Nitrogen is present b) Low nitrogen conc?

Answer 19

a) When nitrogen is present, all cells in vegetive state (no need to form heterocysts)

b) Low nitrogen conc, pero-heterocysts form and after 24 hours heterocysts form

Question 20

Describe how nitrogen limitation causes the differentiation of some vegetive cells of filamentous cyanobacteria into heterocysts

Answer 20

1. Filamentous cyanobacteria grow in nitrogen-rich environments as vegetative cells, carrying out oxygenic photosynthesis and fixing atmospheric carbon dioxide.
2. When the environment becomes nitrogen-limited, the decrease in nitrogen leads to 2-OG (alpha-ketoglutarate) not binding to NtcA (nitrogen control protein)
3. If NtcA not bound to 2-OG, it activates HetR (DNA binding protein) starting gene transcription of genes needed for Heterocyst formation.
4. NctA and HetR increase expression of transcription factor HetF which activates HetR. HetR and NctA form a positive feedback loop where they increase activation of each other more and therefore amplifies Heterocyst gene expression in this cell.
5. PatS and HetN is secreted by the developing heterocyst and diffuses to the adjacent vegetative cells. These prevent adjacent cells from differentiating into heterocysts
6. Now a thick walled N2-fixing heterocyst is formed that imports carbon compounds from neighbouring vegetative cells and exports NH4

Question 21

What are 2 properties of Heterocyst cells for why they can fix nitrogen?

Answer 21

1. Heterocysts contain low content of photosynthetic membranes and only photosystem I (No O2 generation)
2. Thick outer envelope layers; thought to restrict diffusion of oxygen into the cell which might damage nitrogenase

Question 22

What does Sporulation mean?

Answer 22

The formation of spores

Question 23

What is a risk for a) Sporulating too early b) Sporulating too late?

Answer 23

a) Will lose out on vital nutrients

b) Conditions could kill the bacterium

Question 24

What is the most effective strategy for a bacteria to survive stress and why?

Answer 24

Formation of resting cells (spores, cysts, etc) as these cells are metabolic dormant and possess increased resistance against physical and chemical stress.

Question 25

What are 5 examples of spores?

Answer 25

1. Endospores
2. Arial spore
3. Myxospores
4. Small dense cells
5. Elementary bodies

Question 26

What is a type of bacteria that can form endospores?

Answer 26

Bacillus subtilis (gram-positive, rod shaped, found in soil and GI tracts)

Question 27

Describe the 6 stages of endospore development by Bacillus subtilis

Answer 27

1. As the bacterial cell prepares to sporulate, a septum is formed near one end of the cell, dividing it into two unequal compartments: a smaller forespore and a larger mother cell.
2. The mother cell then engulfs the forespore, surrounding it with a double membrane.
3. The mother cell chromosome is then degraded, and its DNA is packaged into the forespore.
4. The forespore is then surrounded by a thick layer of peptidoglycan called the cortex. Coat proteins are also synthesized and assembled around the outer surface of the forespore.
5. Calcium ions and dipicolinic acid (DPA) are synthesized and accumulate within the developing endospore. This helps to stabilize the DNA and other cellular components within the spore.
6. The mother cell lyses, releasing the mature endospore into the environment, where it can remain dormant until conditions are favorable for germination and growth.
   >The peptidoglycan and all materials from mother cell is recycled into the spore (not wasted)

Question 28

Describe the role of Sigma factors in endospore development of Bacillus subtilis in 5 steps

Answer 28

1. Sigma H activated first responsible for the early stages of sporulation, including the formation of the spore septum, and activation of Sigma F
2. Sigma F expression increases in forespore and initiates transcription of genes for engulfment of forespore by mother cell.
3. Once engulfment is complete, Sigma F is degraded, and Sigma E (present in mother cell) is activated. Sigma E initiates transcription of genes that are involved in the middle stages of spore formation, including initiating synthesis of spore coat proteins.
4. Once the spore coat is complete, Sigma E is degraded, and Sigma G (in forespore) is activated. This activates Sigma K (in mother cell).
5. Sigma K transcribes genes to mature the spore for harsh environments and assembles the spore coat.

Question 29

What is the purpose of the sigma factor cascade in sporulation?

Answer 29

Cascade makes sure sporulation occurs in correct order.

Answer 30

1. Dehydrated core:
   >During spore formation, the core of the spore becomes dehydrated, e.g. in Bacillus because of accumulation of Dipicolinic acid (DPA)
2. Small acid-soluble spore proteins (SASPs):
   >SASPs are highly resistant to heat, radiation, and chemicals. During sporulation, the bacterial cell synthesizes SASPs and deposits them in the spore core, where they bind to and protect the DNA from damage.
3. Ca(II)DPA: Calcium dipicolinate (Ca(II)DPA)
   >A complex molecule that binds to the DNA in the spore core, helping to protect it from damage. During sporulation, the bacterial cell synthesizes and deposits high levels of Ca(II)DPA in the spore core, which increases the spore’s resistance to heat, radiation, and chemicals.
4. Coat:
   >The spore coat is composed of a complex mixture of proteins, lipids, and carbohydrates, which helps to protect the spore from chemical and physical stress. The spore coat is highly impermeable to most chemicals and organic solvents.

Question 31

What is different between endospore formation in Bacillus subtilis and spore formation in Myxobacteria?

Answer 31

1. During formation of endospores, the cell undergoes an unequal division in a mother cell resulting in a mother cell and a prespore cell.
   >Has peptidoglycan wall as endospore synthesises a coat (more protective against physical and chemical conditions).
   >Has one chromosome, as mother cell chromosome is degraded
2. During formation of myxospores, the entire cell will become spherical and turn into a spore.
   >As the morphology changes, peptidoglycan wall must disappear, so Myxospores don’t have peptidoglycan wall.
   >Contains two chromosomes (if one is damaged spore will still survive)
   >Myxococcus cells also produce glycerol spores in response to substances like glycerol that interfere with cell growth.

Question 32

Is sporilation the last resort?

Answer 32

Yes as once started cannot be undone until germination occurs

> Strignent response (stress response by sigma factors)