Chapter 4 Part 4

1. 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. 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 Fimbriae and Pili

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