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Surface structures and inclusions of prokaryotes

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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

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