Lecture 19: Bacterial Cell Division

DNA replicates first then divides down the middle. How does division actually occur?

1. DNA replicates first, ensuring each daughter cell receives a copy

2. The cell elongates as chromosomes move apart

3. The septum forms, splitting the cell

Who are the main players in bacterial cell division?

FtsZ, ZipA, FtsA, FtsK, and FtsI

FtsZ

• Forms ring around center of cell

• Homolog of tubulin

• Uses GTP to create FtsZ ring

What does FtsA and ZipA do?

FtsA helps connect FtsZ ring to membrane and also recruits other divisome proteins while ZipA anchors the FtsZ ring to cytoplasmic membrane

What are FtsI and K doing?

FtsI mediates peptidoglycan synthesis while FtsK mediates separation of chromosomes to daughter cells

What is the job of the MinCDE proteins?

Make sure FtsZ ring is formed in correct location

Specifically what is C, D, and E doing in cell division regulation?

• MinC: Blocks FtsZ polymerization at incorrect locations (inhibits Z-ring formation).

• MinD: Binds to the cell membrane and recruits MinC and Helps oscillate MinC between the poles.

• MinE: Creates pulsing oscillations that push MinC/D toward the poles and Ensures FtsZ assembles in the center of the cell.

What is the job of SlmA?

Prevents FtsZ polymerization over the nucleoid (prevents "guillotining" the chromosome)

When does SulA come into the picture?

When DNA damage is detected

What is SulA’s job?

Inhibits FtsZ polymerization to delay division, giving time for DNA repair before the cell divides.

Bacterial cell division process

1. DNA Replication: The bacterial chromosome is duplicated before division.

2. MinCDE Oscillation: Prevents FtsZ from forming anywhere except the middle.

3. SlmA Action: Ensures FtsZ does not form over the nucleoid.

4. FtsZ Forms the Z-Ring: Recruits division proteins (FtsA, ZipA, etc.).

5. Peptidoglycan Synthesis (FtsI): Cell wall material is built at the septum.

6. FtsK Helps Chromosome Partitioning: Ensures DNA is correctly segregated.

7. Cell Divides: The septum constricts, splitting the cell into two.

What does Senescence mean?

Cells growing older

clones of each other but not the same age, how?

Both daughter cells inherit older pole, which is then passed down through multiple generations

senescence - How does this effect growth?

Cell with older pole grow slower than those with newer poles

What does a typical bacterial growth curve look like?

What are the four phases of bacterial growth called?

Lag, log/exponential/ stationary, and death

Lag phase

Cells are adjusting to their new environment, metabolically active but not dividing yet

log/exponential phase

Rapid binary fission; cells are growing at their maximum rate

stationary phase

Growth slows as nutrients deplete, waste accumulates; cell death = cell division

death phase

Nutrients are gone, toxic byproducts accumulate, cells die faster than they divide

When are spores made?

Stationary phase

When does horizontal gene transfer happen?

Stationary phase

When do antibiotics work best?

log/exponential phase

Why does bacterial growth curve look smooth and not staircase like?

Growth is exponential, not perfectly synchronized

What does asexual reproduction mean?

Organism creates offspring without combining genetic material with another organism

What does doubling time mean?

Time it takes for a bacterial population to double in number

What is the difference between synchronous and nonsynchronous growth?

Synchronous is when all cells divide at the same time

nonsynchronous is when cells divide at slightly different times

how do bacteria grow?

nonsynchronously

If a cell divides every 20 min, when do I know I am sick?

When cell bacteria reaches 1 million cells

• Ex: 6.66 hours (E. coli)

What about if it doubles every 2 weeks? when do I know I am sick?

9.33 months (M. tuberculosis)

If I have 4 cells and they go through 4 rounds of replication, how many bacteria do I have?

4*2^2 = 64