Chapter 4 Part 4

Surface structures and inclusions of prokaryotes

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

Capsules and Slime Layers

– Polysaccharide layers

– Assist in attachment to surfaces

– Aid in evasion of immune system

– Resist dessication

Capsule

• Observed by using a negative stain

• The dye does not penetrate the capsule but is seen on a dark background

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)

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

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

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

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

Differences between Endospores and Vegetative Cells

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

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

Spore structure

Sporulation or Sporogenesis

• Process of endospore formation within a vegetative (parent) cell

• Germination = return of an endospore to its vegetative state

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

Microbial locomotion

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

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

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

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

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

Gliding motility: movement of proteins

• Motility proteins in the cytoplasmic and outer membranes propel the cell

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

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

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

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

Chemotaxis