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Bacteria
&
Gram Staining
Origins - Three Domain Classification
EU
PROKARYOTES
Prokaryotes & Eukaryotes
Prokaryotic Cells
Genetic Material
Organelles
DNA not bound by
membrane; DNA
usually a singularly
circular
chromosome
Lacks membranebound organelles
Cell Wall
Cell walls contain
peptidoglycan
Cell Division
Usually Binary
Fission
Eukaryotic Cells
DNA found in a
nucleus; DNA
contained in
multiple
chromosomes
Contains
membrane-bound
organelles
Cell walls are
usually chemically
simple
Mitosis
Origins



First formed about 3.5 billion years
ago
FIRST LIFE FORMS WERE Archaea, or
ancient bacteria
Eubacteria is true bacteria
(Eu = true)
 Eukaryote = true nucleus
Archaea
• Primitive bacteria
• Live in extreme or harsh environments
• 3 kinds:
– Halophiles= live in very basic or salty
environments
• Great Salt Lake
• Dead Sea
– Methanogens= don’t require O2 to live, make
methane gas (CH4) as product of respiration
– Thermophiles= live in hot or acidic
environments (~pH 1-4)
• Near undersea volcanic vents
• Sulphur Springs
• Hot springs in Yellowstone National Park
Eubacteria
 Ubiquitous = they exist everywhere
 Harmful – pathogenic (they cause
disease)
 Helpful – they have a variety of uses
Bacterial Uses!!
• Food & Drink Production
– Fermentation (drinks)
– Baking (Baker’s yeast)
• Sewage Decomposition
– Bacteria break down the organic matter
• Nitrogen Fixation in roots
– Helps plants take up H2O and nutrients from
soil
Bacterial Uses!!
• Mining
– Bacteria concentrate desired elements from ore
• Bioremediation
– Microbes can help repair damaged ecosystems
• Human Recreation = Artificial Snow-Making
– Bacteria allow H2O to form ice crystals
Bacterial Classification
1. Shape and Groupings
2. Cell wall composition
3. Environment
4. DNA Sequences
Bacterial Cell
Bacterial Structure

Cell Wall
Prevents cell from rupturing
 Composition of cell wall helps to identify
bacteria


Cell Membrane
F(x) = support & protect
 Differentially permeable


Cytoplasm

Contains organelles (non-membranous)
Bacterial Structure
 Genetic
Material
 Single,
circular chromosome
 Plasmid = extra chromosome that can
replicate separately from the main
chromosome
•
•
Can be used as a vector for biological
engineering
Can pass genes for antibiotic resistance
onto other bacteria (sometimes resistance
to several antibiotics @ one time)
Bacterial Structure

Ribosomes


F(x) is to synthesize proteins
Capsule (Slime Layer)
A viscous coating on the outside of a bacteria
 Exterior to the cell wall
 F(x)s:
• Protection
• Increases a bacteria’s pathogenicity (or
ability to cause disease)
• Protects bacteria from the Immune System
(WBC’s)

Bacterial Structure
 Other
structures (Appendages)
 Flagella
•
•
F(x) = locomotion
Cell can have one, two, or many
 Pili
•
(hair-like extensions)
F(x)s = attachment to host and transfer of
genetic material
 Fimbrae
•
(protein appendage)
(shorter than pili)
F(x) = adhesion to surfaces
Flagella
Flagellar
Movement
Bacterial Shapes

Typical

Coccus/Cocci = spherical or round

Bacillus/Bacilli = rod-shaped

Spirillum/Spirilli = spiral-shaped

Spirochete = helical-shaped

Vibrio/Vibrios = curved rod

Coccobacillus = very short rod
Bacterial Shapes
Bacterial Shapes
 Atypical
 Pleiomorphic = vary in size and shape
Star-shaped
Rectangular or Cube-shaped
 Mycoplasms = can change shape
Lack a rigid cell wall
Have a strong cell membrane
Bacterial Groupings
 Groups determined by the plane
in which the cell divides
Bacterial
Groupings
– 1 plane =
• diplo- (pair)
• strepto- (chain)
– 2 planes =
• tetrad (packet of 4)
– Several planes @
random =
• staphylo(grape-like clusters)
GRAM STAINING
• History & Definitions
– Developed by Hans Christian
Gram in 1884
– Used to help identify different types
of bacteria (a differential stain)
– Stain uses differences in cell wall
composition to differentiate between bacteria
– The most common/popular method for
staining bacteria
– Can help determine which type of antibiotics
will be most effective against a particular
bacteria
Gram Positive Cells
• Stain purple
• Contain:
– A thick peptidoglycan layer + teichoic
acids (cell wall)
– Sits on top of the plasma membrane
– This layer is permeable to small molecules
• More susceptible to Penicillin
Gram Positive Cell
• Stain pink/light red
• Contain (triple layer):
– A outer layer of lipopolysaccharides + outer
membrane
(space)
– A thin layer of peptidoglycan
(space)
– A cell membrane
– Porin proteins in the outer membrane allow larger
molecules to pass
• Less susceptible to Penicllin
Gram Negative Cell
Outer Layer
Cell Wall
Cell Membrane
Penicillin
• Antibiotic that inhibits the synthesis of
peptidoglycan; used on actively growing
organisms.
– Gram (+) cells  Penicillin can get to the
peptidoglycan layers
– Gram (-) cells  Pencillin has a harder time
attacking the peptidoglycan layers
– Some Penicillin derivatives can pass through
the porin proteins of Gram (-) cells
Overview of Staining
Why do we stain?
•To better view a cell’s structure.
Gram Staining Procedure
Steps (abbreviated):
1) Add primary (1o) stain – Crystal Violet
2) Add mordant to cells – Iodine
3) Add decolorizer to cells – Alcohol
4) Add secondary (2o) stain - Safranin
Gram Staining Steps