1. Surface structures and inclusions of prokaryotes
Chapter 4 Part 4
Surface structures and inclusions of prokaryotes

2. Glycocalyx Substance that surrounds the cell
Gelatin polymer containing sugars and proteins
If firmly attached to the cell wall = capsule
If loosely attached to the cell wall = slime layer
Functions
attachment
protection of pathogen from host immune system
protection from phagocytosis
resistance to desiccation

3. Capsules and Slime Layers
Polysaccharide layers
Assist in attachment to surfaces
Aid in evasion of immune system
Resist dessication

4. Capsule Observed by using a negative stain
The dye does not penetrate the capsule but is seen on a dark background

5. S layer Cell surface layer composed of protein
Almost always in archaea (cell wall type) and in many bacteria (associates with cell wall, cell memrane, or LPS)
Function not precisely known
May act as a selectively permeable barrier
bacteria: may provide protection from host defense (pathogens)

6. Fimbriae and Pili Hairlike appendages that are shorter than flagella
Used for attachment
Pili: longer than fimbriae
Conjugation with pili
Join bacterial cells in preparation for the transfer of DNA from one cell to another

7. Inclusion bodies
Function as energy reserves or as a reservoir of structural building blocks
Differ in different organisms
Carbon storage polymers
Polyphosphates
Sulfur globules
Magnetosomes
Gas vesicles

8. Endospores
Resting structures formed by some bacteria for survival during adverse environmental conditions
Example: when essential nutrients are depleted
The endospore is a highly resistant differentiated bacterial cell that are highly resistant to heat, and drying out and are difficult to destroy

9. Endospores
Endospores can remain dormant indefinitely but germinate quickly when the appropriate trigger is applied
Endospores differ significantly from the vegetative, or normally functioning, cells

10. Differences between Endospores and Vegetative Cells

11. Important spore proteins
Dipicolinic acid
Located in the core
Calcium-dipicolinic acid complexes reduces water available and helps dehydrate spores
Interculates into the DNA and stabilizes it to heat denaturation

12. Important spore proteins
Small acid-soluble proteins (SASPs)
Bind to the DNA in the core and protect it from damage
Function as a carbon and energy source when forming vegetative (normal) cells from spore cells

13. Spore structure

14. Sporulation or Sporogenesis
Process of endospore formation within a vegetative (parent) cell
Germination = return of an endospore to its vegetative state

15. Spore Germination Activation by heat and nutrients
Ca-dipicolinate and cortex components disappear
SASPs degrade
Swelling with H2O
Cell begins to divide like normal
Bacillus anthracis (and Clostridium) produces endospores
Easily aerosolized and spread
Relatively easy and inexpensive to prepare in laboratory
Can be easily transported without detection

16. Microbial locomotion

17. Flagella
Long filamentous appendages that propel the bacteria in movement
made of several proteins, most of which are anchored in the cell wall and cytoplasmic membrane
The flagellum filament, rotates which drives the flagellar motor

18. Different types of flagella
In peritrichous flagellation, the flagella are inserted at many locations around the cell surface
In polar flagellation, the flagella are attached at one or both ends of the cell.
In lophotrichous flagellation, a group of flagella arise at one end

19. 3 parts of flagella
Filament: long outermost region; flagellin subunits (Flg units); attached to the hook
Hook: base; single protein, connection to motor
Motor (basal body): anchors the flagellum to the cell wall and the plasma membrane
Flagella moves the cell by rotating from the motor either clockwise or counterclockwise

20. Gliding motility
Prokaryotes that move by gliding motility do not employ rotating flagella but instead creep along a solid surface by any of several possible mechanisms
Movement typically occurs along long axis of cell
Slower than flagella; 10 μm/sec
Myxobacteria and Cyanobacteria examples

21. Gliding motility: slime secretion
Polysaccharide slime is secreted on the outside surface of the cell
Slimes contacts the cell surface and solid surface upon which it glides
As slime adheres, the cell is pulled along the surface

22. Gliding motility: movement of proteins
Motility proteins in the cytoplasmic and outer membranes propel the cell

23. Why do bacteria move?
Motile bacteria can respond to chemical and physical gradients in their environment
Movement toward an attractant
Movement away from a repellant
Controlled by the degree to which runs (counterclockwise) or tumbles (clockwise) occurs - direction of rotation of the flagellum

24. Types of movement
Taxis: directed movement in response to chemical or physical gradients
Chemotaxis: a response to chemicals
Phototaxis: a response to light
Aerotaxis: a response to oxygen
Osmotaxis: a response to ionic strength
Hydrotaxis: a response to water

25. Direction of movement
Counterclockwise rotation moves the cell in a direction called a run
Clockwise rotation causes the tuft (group) of flagella to spread, resulting in tumbling of the cell

26. Chemotaxis No attractant, random runs and tumbles but do not move
When there is an attractant, the runs are longer and the tumbles are less frequent
Result is that the organism moves towards the attractant

27. Chemotaxis