lectures 3-4 bacteriology

What type of cell division do bacteria use?

Binary fission

What is generation time?

Time required to complete one cell division cycle

How long is generation time typically?

20-30 mins but can be as short as 5-10 mins under optimal conditions

What is the formula for exponential growth in bacteria?

Nt = N0 x 2^n

Nt = population at time, t

N0 = initial population at time 0

n = number of generations elapsed

Does exponential growth continue indefinitely?

No, it is limited by factors like competition and toxic products

What two mechanisms ensure septum formation at the midcell?

1. Nucleoid occlusion - prevents septum formation near the nucleoid

2. MinCDE system - inhibits septum formation at the poles

What are filamentous temperature-sensitive (fts) genes?

Genes involved in cell division - become non-functional at higher temperatures

Why are fts genes non-functional at higher temperatures?

Become filamentous and cannot divide properly

What does the fts gene ftsZ encode?

A tubulin homologue

What structure does FtsZ form in vivo?

A Z ring

How many subunits of FtsZ form the Z ring?

10,000 - 20,000 subunits

What is the function of the Z ring?

It recruits other proteins to form the divisome and constricts to create daughter cells

What proteins stabilise and connect the Z ring to the membrane?

FtsA - ATPase that also recruits other proteins

ZipA - stabilises the Z ring

What protein is involved in peptidoglycan synthesis?

Ftsl

What protein aids chromosome separation?

FtsK

What is nucleoid occlusion and what proteins does it utilise?

A mechanism that blocks Z ring formation near the nucleoid using proteins SlmA and Noc

How does SlmA affect Z ring formation?

High concentrations of SlmA block FtsZ polymerisation, preventing Z ring formation

What is the role of the Min system?

Prevents septum formation at the poles by creating a concentration gradient

How do Min proteins behave in the cell?

Oscillate from pole to pole to inhibit septum formation

What are the components of the Min system? Describe their roles.

MinC - inhibits Z ring formation

MinD - ATPase that forms a membrane-bound complex with MinC

MinE - Activates MinD ATP hydrolysis and forms dynamic ring structure that oscillates from pole to pole of the cell

Distribution of Min proteins in the cells

Highest concentration at poles, lowest at mid cell

What happens as the Z ring constricts?

FtsZ depolymerises and peptidoglycan synthesis generates force for constriction

What energy source drives Z ring depolymerisation?

GTP hydrolysis by FtsZ

What are bacterial flagella made of?

Protein subunits called flagellin

What is the function of flagella

Provide motility for movement toward or away from stimuli

What powers the rotation of flagella?

An ion-powered rotary motor embedded in the cell membrane

Name and briefly describe the four types of flagellar arrangements

1. Monotrichous - single flagellum at one pole

2. Lophotrichous - multiple flagella at one pole

3. Amphitrichous - flagella at both poles

4. Peritrichous - flagella distributed all over the cell surface

How fast can bacterial flagella rotate?

Up to 300 revolutions per minute

What movement patterns are caused by flagella?

1. Counterclockwise - flagella bundle together and propel the cell forward (run)

2. Clockwise - flagella separate, causing tumbling and reorientation (tumble)

Describe the three main components of the flagellum

1. Filament - long, whip-like structure made of flagellin

2. Hook - connects the filament to the basal body

3. Basal body - anchors the flagellum to the cell membrane and powers rotation

Rod function

Connects basal body to hook

FliF protein

Forms the MS ring, anchoring the flagellum

FlgD protein

The hook protein that links the basal body and filament

FliK protein

Ensures the hook is the correct length

FlgJ protein

Acts as the rod cap and aids in rod assembly

What proteins form the C-ring and enable rotation?

FliG, FliM, FliN

How are proteins exported for flagellar assembly?

Through the type II secretion system

How do C-ring proteins contribute to motility?

FliG, FliM and FliN interact with motor proteins to generate torque for flagellar rotation