Exam 2 Bacterial Structures 10/10 Flashcards
The bacterial cell surface:
Biofilms provide protection and enhanced survivability in harsh environments.
Slime Layers
similar to capsules except diffuse, unorganized and easily removed
Usually composed of polysaccharides but not easily seen with a light microscope
slime may aid in motility
e.g. Xanthamonas campestris
Glycocalyx usually refers to both capsules and slime layers
S Layers
regularly structured layers of protein or glycoprotein that self-assemble
Gram-negative bacteria the S layer adheres to outer membrane
Gram-positive bacteria it is associated with the peptidoglycan surface
S Layer Functions
protect from ion and pH fluctuations, osmotic stress, enzymes, and predation
maintains shape and rigidity
promotes adhesion to surfaces
protects from host defenses
potential use in nanotechnology
The bacterial cell surface: Arrays
Surface arrays (S-layers)
Crystalline array of interlocking proteins
Found in Gram-positive and Gram-negative cells
The Bacterial Endospore
complex, dormant structure formed by some bacteria
resistant to numerous environmental conditions
- heat
- radiation
- chemicals
- desiccation
Examples of Endospore Locations
Central
Subterminal
Terminal
Swollen sporangium
What Makes an Endospore so Resistant?
calcium (complexed with dipicolinic acid)
small, acid-soluble, DNA-binding proteins (SASPs)
dehydrated core
spore coat and exosporium protect
Sporulation
process of endospore formation
occurs in hours (up to 10 hours)
normally commences when growth ceases because of lack of nutrients
complex multistage process
Germination
transformation of endospore into vegetative cell complex, multistage process
Formation of Vegetative Cell
activation
- prepares spores for germination
- often results from treatments like heating
germination
- environmental nutrients are detected
- spore swelling and rupture of absorption of - spore coat
- loss of resistance
- increased metabolic activity
outgrowth - emergence of vegetative cell
Bacterial taxonomy:
Standard binomial nomenclature
Species: group of strains sharing common features, while differing considerably from other strains
Genus: group of closely related species
Bacterial taxonomy: Classification depends on many features
Size/shape
Gram type
Colony morphology
Presence of structures such as capsules/endospores
Physiologic/metabolic traits (see Ch. 13)
DNA sequence data (in more recent years)
Bacterial taxonomy: Once classified, microbes are deposited in at least two culture collections.
The World Federation for Culture Collections maintains a database of more than 500 collections from over 60 countries.
These are pure, maintained cultures made available to scientists for research purposes.
