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 H 2 O • Cell begins to divide like normal

Bacillus anthracis

endospores (and

Clostridium

– Easily aerosolized and spread ) produces – 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 • In

peritrichous

flagellation, the flagella are inserted at many locations around the cell surface • In end

polar

flagellation, the flagella are attached at one or both ends of the cell.

lophotrichous

flagellation, a group of flagella arise at one

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