S layers

• outer most layer, serves as the last bit of protection from the outside world
• commonly in archaea, sometimes in bacteria
• composed of interlocking protein or glycoprotein
• has a paracrystalline surface layer

paracrystalline surface layer

• keeps proteins near the cell surface
• only allows small solutes through 
• can resist osmotic pressure, such as pressure exerted from the peptidoglycan layer 

components of a polysaccharide layer

• capsules
• slime layer
• EPS

capsules

• a tight matrix thast firmly attached to the cell wall
• keeps small particles out
• helps bacterial cells enter the body and go undetected

slime layer

• loosely attached to the cell surface, and can separate be lost
• difficult to see
• does NOT keep out small particles

EPS

• extracellular polysaccharide
• involved in biofilm formation (which helps cell adhere and resist antibiotics, slowing down the rate of metabolism)
• also help with motility in aqueoud environments (pilus binding and twitching motility)

types of cell surface appendages

• pili/fimbriae
• flagella

pili

• made up of long strands of protein
• serve as a receptor for viruses
• involved in adherence and binding to the surface
• is retractable
• involved in DNA exchange (conjunction)
• causes twitching motility

twitching motility

• Type IV pili involved
• type of gliding movement along a solid surface
• extension and then retraction of the pili causes the cell to glide along the surface
• requires ATP for energy

fimbriae

• made up of protein
• allow cells to stick to the surfaces and form pellicles
• NON retractable

flagella

• rotary-motor controlled
• Polar (either one or both ends of the cells)
• causes swimming motility
• tuft - group of flagella
• flagella biosyntehsis begins at the bottom and ends with the hook and filament

3 types of flagella

• lophotrichous - one at one end of the cell 
• peritrichous - found all over the surface of the cell
• amphitrichous - found at both ends of the cell 

taxes

directional movement

3 types of taxis

• phototaxis
• aerotaxis
• chemotaxis

phototaxis

• movement towards a light source
• photosynthetic bacteria

aerotaxis

• movement towards high/low concentration of oxygen
• cynobacteria

chemotaxis

• movement towards attractants or away from repellants
• movement is directed
• going up the gradient makes the cell run longer
• going down the gradient causes the cell to rumble more often 
• causes swimming motility

gas vesicles

• gas filled cytoplasmic structure that are water tight
• bounded by protein
• causes buoyancy in the cell
• allows the cells to move up the water column to reach better light for photosynthesis

carbon storage inclusion

• from glycogen to polyhydroxybutrate
• PH4 storage inclusion