Microbiology Lecture 6

Storage Polymers

An Internal Cell Structure. They act like stored supplies that bacteria can use when nutrients or energy are needed.

Poly-β-hydroxyalkanoate (PHA)

Glycogen

Polyphosphates

Sulfur granules

Poly-β-hydroxyalkanoate (PHA)

A storage polymer. A polyester that stores carbon and energy.

Glycogen

A polymer made of many glucose molecules; stores carbon and energy.

Polyphosphates

Stores phosphates and energy.

Sulfur granules

energy storage for certain sulfur bacteria.

Food Storage

When there is plenty of hydrogen sulfide, sulfur bacteria oxidize sulfide into elemental sulfur, releasing 2 electrons for energy. They store the Sulfur inside the cell as the dark circular granules.

Certain bacteria store sulfur when it is abundant and consume that stored sulfur later when their external sulfur source runs out.

Functional Structures

Ribosomes

Carboxysomes

Ribosome

site of protein synthesis in all cells

Carboxysome

protein shell, contains enzymes for CO2 fixation in some bacteria. CO2 fixation just means that CO2 is removed from the air and turned into glucose.

How does a Carboxysome convert CO₂ into sugar efficiently?

Rubisco is the enzyme that fixes—or captures—CO₂ and uses it to begin making sugars.

The carboxysome’s protein shell keeps Rubisco and a high concentration of CO₂ close together. This makes it more likely that Rubisco will bind to CO₂.

This is helpful because oxygen (O2O_2) interferes with Rubisco. Rubisco can accidentally bind oxygen instead of CO₂, which reduces sugar production.

Survival Structures Example

-Endospores

How do endospores form?

A vegetive cell will copy its DNA and divide unevenly into a mother cell and a forespore. The mother cell surrounds and engulfs the forespore. The mother cell is the sporulating cell.at Protective layers form around it. The endospore develops. The mother cell breaks open, releasing the mature endospore.

What kind of conditions can endospores withstand? What acid does it have and why is it helpful?

Highly resistant to heat, drying, harsh chemicals, and radiation

Also has dipliconic acid, a unique molecule that promotes desiccation. (state of being extremely dry)

The controlled desiccation makes it so that an extreme heat environment does not hurt the cell.

What kind of cells are endospores and when do they transition?

Endospores are dormant cells, ideal for survival and dispersal

Germinate into a vegetative cell when conditions favor growth

What bacterial family are endospores found in?

Found in the families Bacillales and Clostridiales of the phylum “Firmicutes”

What does endospore germination mean?

Germinate means that a dormant endospore “wakes up” and develops into an active, growing bacterial cell.

vegetative cells

Growing cells

Germination signals

Nutrients and (moderate) heat are germination signals

glycocalyx

An external cell structure.

Usually made up of polysaccharides.

Has two forms:

-The capsule: Tightly attached

-Slime layer: Loosely attached.

Why is the Glycocalyx important?

Assists in attachment to surface.

Resist drying. Keeps bacteria hydrated.

Protects against phagocytosis. (A protection from antibodies and immune system)

Fimbriae

An external cell structure.

Short filamentous protein structures. Assists in nonspecific attatchments.

Pili

External Cell Structures

-Long filamentous, dynamic protein structures

-Assists in attachment

-Facilitate conjugation: direct transfer of DNA between bacterial cells through cell-to-cell contact.

-Polymerizes/ Depolymerizes

-Type IV pili are involved in twitching motility.

Flagella

Long helical protein structures

Enables swimming motility

Able to rotate

Induce an immune response

Types of Flagella

Peritrichous: Flagella surround the entire perimeter of the cell.

Polar: One single flagella at a pole.

Lophotrichous: Many flagella coming out from 1 pole.

Bacterial Flagellum depend on what as an energy source?

Bacterial flagellum is.a proton motif force driven motor.

Swimming motility in Flagella

-Bacteria and Archea depend on flagella for motility.

-Some cells are really fast.

What direction can flagella be?

Flagella can be either reversible or unidirectional

Taxis

directed movement in response to chemical or physical gradients

Chemotaxis:

Directed movement in response to chemicals.

Phototaxis

Directed movement in response to light.

Aerotaxis

Directed movement in response to oxygen.

Osmotaxis

Directed movement in response ionic strength.

Hydrotaxis

Directed movement in response water.

Chemoreceptors

Detect these signals. Chemoreceptors sense changes in chemical concentration over time

How does location affect how bacteria change and move direction?

bacteria move and change direction depending on where their flagella are located.

Peritrichous flagella Counterclockwise rotation

The flagella bundle together and propel the bacterium straight forward.

Peritrichous flagella Clockwise (CW) rotation

The flagella separate and push in different directions, making the bacterium tumble and randomly reorient.

Polar flagella Reversible flagellum

Counterclockwise (CCW) rotation moves the bacterium in one direction.

It switches to clockwise (CW) rotation, causing the bacterium to move in the opposite direction.

Polar flagella Unidirectional flagellum

The motor only rotates in one direction. To change direction, the cell briefly stops, reorients itself, and then resumes swimming.

E. coli movement behavior

E. coli exhibits “Run and tumble” behavior resulting in a “biased random walk”

No Attractant present

The bacterium alternates between runs and tumbles without favoring any direction. Its overall movement is random.

Attractant present

If the attractant concentration increases, the cell recognizes that it is moving in a good direction. It tumbles less and continues the same run for longer.If the attractant concentration decreases, the cell recognizes that it is moving in a bad direction. It tumbles sooner, randomly chooses a new direction, and tries again.

Bacterial Flagella

• Swimming motility

• Helical filament composed of flagellin protein

• Uses proton motive force to rotate

Archaella of Archaea

• Swimming motility

• Helical filament composed of archaellin protein

• Uses ATP to rotate

Endoflagella

Immune system cannot detect it. Wiggles around flagella to move.

Twitching Motility:

Requires surface attachment by Type IV pili

ATP dependent pilus retraction

Very slow

Gliding motility:

Requires surface attachment

Complex molecular mechanism

Uses proton motive force for energy

Magnetosomes

An internal structure.

Bacteria can make little magnets inside of them. Used to orient themselves.

Gas Vacuoles

An internal cell structure

A protein shell filled with gas to provide buoyancy.

Biominerals

An internal cell structure who’s purpose is widely unknown.

ex) carbonate minerals