Bacteria
An Overview
Bacteria
Bacteria is the plural of bacterium
 Prokaryotic cells – no true nucleus
 Have one double stranded chromosome
 May have additional DNA called a plasmid
 Reproduce by binary fission
 Most are benign
 Some are pathogenic

Kingdoms
Two kingdoms include prokaryotic cells
 Archaebacteria

◦
◦
◦
◦
◦

Extremophiles
Methanogens - intestines
Halophiles - salt
Thermophiles – heat tolerance
May have been on Earth for 3.5 billion years
Eubacteria – all other bacteria
Archeabacteria
Thermophile research in Yellowstone has
also proved benefical to the field of
astrobiology.
 Many scientists believe that thermophiles
are most closely related to the primordial
origin of life and can provide insight into
early Earth as well as expand possiblities
for life elsewhere in the universe

Archaebacteria
Thermophile mats
Grand Prismatic
Filamentous Bacteris
Yellowstone
Archaebacteria
Salt crust is colored red by dense colonies
of halophilic archaebacteria. Sierra Nevada
Halophilic bacteria surviving in salt crystals.
Owens Valley, California
Characterizing Eubacteria

Bacteria can be characterized by shape
Characterizing Bacteria
Bacteria is also classified by their oxygen
requirements
 Aerobic Bacteria require oxygen to
support reproduction

◦ Esherichia coli

Anaerobic bacteria reproduce in the
absence of oxygen
◦ Listeria
◦ Clostridium botulinum
Characterizing Bacteria

Facultative bacteria reproduce either in
the presence or in the absence of oxygen.
◦ Salmonella
◦ Staphylococcus aureus
Characterizing Bacteria
Bacteria secrete a covering for
themselves - cell wall
 Do not contain cellulose like plant cell
walls
 Mostly made of peptidoglycan
(polypeptides bonded to modified sugars)
 the amount & location of the
peptidoglycan are different in the two
possible types of cell walls, depending on
the species of bacterium

Characterizing Bacteria
Some antibiotics, like penicillin, inhibit the
formation of the chemical cross linkages
needed to make peptidoglycan.
 These antibiotics don’t outright kill the
bacteria, but just stop them from being able
to make more cell wall so they can grow.
 That’s why antibiotics must typically be taken
for ten days until the bacteria die (unable to
grow)
 If a person stops taking the antibiotic sooner,
any living bacteria could start making
peptidoglycan, grow, and reproduce.

Characterizing Bacteria

Dr. Hans Christian Gram, a Danish
physician, invented a staining process to
tell the two types of bacteria apart, and in
his honor, this process is called Gram
stain.
Gram Stain
the amount of
peptidoglycan in the
cell walls of the
bacteria determine
how those bacteria
absorb the dyes
with which they are
stained
 bacterial cells can be
Gram+ or Gram -.

E.Coli and Strep
Gram Stain

Gram+ bacteria have simpler cell walls
with lots of peptidoglycan, and stain a
dark purple color.
Anthrax
Gram Stain

Gram- bacteria have more complex cell
walls with less peptidoglycan, thus absorb
less of the purple dye used and stain a
pinkish color instead
Pseudomonus aerugenosa
E.coli
Gram Stain
Gram- bacteria often incorporate toxic
chemicals (called endotoxin) into their
cell walls, thus tend to cause worse
reactions in our bodies.
 antibiotics like penicillin are less effective
against gram negative bacteria.
 Ampicillin was developed to treat gram
negative bacteria

Gram Stain

Gram staining involves a four-part
process, which includes:
◦
◦
◦
◦
crystal violet, the primary stain
iodine, the mordant
a decolorizer made of acetone and alcohol
safranin, the counterstain