Bacteria and Archaea
KEY CONCEPT
Bacteria and archaea are both single-celled
prokaryotes.
Bacteria and Archaea
Bacteria and Archaea
Prokaryotes are widespread on Earth.
• Prokaryotes can be grouped by their need for oxygen.
– obligate anaerobes
are poisoned by
oxygen
– obligate aerobes
need oxygen
– facultative aerobes
can live with or
without oxygen
Bacteria and Archaea
• Bacteria commonly come in three forms.
– rod-shaped, called bacilli
– spiral, called spirilla or spirochetes
– spherical, called cocci
Lactobacilli: rod-shaped
Spirochaeta: spiral
Enterococci: spherical
Bacteria and Archaea
• Bacterial Cell Structure.
– No nucleus
– Chromosomal DNA
plasma
– Plasmid (circular DNA
membrance
with only 3 or
chromosome
4 genes)
cell wall
– Flagellum
plasmid
– Pili
– Cell Wall
This diagram shows the typical structure
of a prokaryote. Archaea and bacteria look
very similar, although they have important
molecular differences.
pili
flagellum
Bacteria and Archaea
• Gram Positive and Negative is based on the composition
of the cell wall.
– Gram Positive have 1 cell wall
– Gram Negative have 2 cell walls with less
peptidoglycan
GRAM NEGATIVE
GRAM POSITIVE
Bacteria and Archaea
• Gram staining identifies bacteria.
- gram-positive stains purple (antibiotics work)
- gram-negative stains pink (resistant to many
antibiotics)
Gram-negative bacteria have a thin layer of
peptidoglycan and stain red.
Gram-positive bacteria have a thicker
peptidoglycan layer and stain purple.
Bacteria and Archaea
Bacteria Reproduce through Binary Fission
• Binary fission is like mitosis
– One cell creates 2 identical daughter cells
– Can occur once every 20 minutes
Bacteria and Archaea
Bacteria have various strategies for survival.
• Prokaryotes
exchange genes
during conjugation.
– Most of the time,
plasmids move
through the
conjugation
bridge.
conjugation bridge
TEM; magnification 6000x
Bacteria and Archaea
Bacteria can evolve resistance to antibiotics by mutation,
and then pass it to others through conjugation.
A bacterium carries genes for antibiotic
resistance on a plasmid.
A copy of the plasmid is transferred through
conjugation.
Resistance is quickly spread through many
bacteria.
Bacteria and Archaea
Bacteria may survive by forming endospores.
• Endospores are
thick cell walls
that protect
bacteria in harsh
environments.
– The cell goes
dormant
• When conditions
become
favorable, the
endospore
dissolves and the
cell wakes up.
Bacteria and Archaea
Prokaryotes provide nutrients to humans and other
animals.
– make vitamins
– break down food
Bacteria and Archaea
• Bacteria help ferment many foods.
– yogurt, cheese
– pickles, sauerkraut
– soy sauce, vinegar
Bacteria and Archaea
Prokaryotes play important roles in ecosystems.
– photosynthesize
– recycle carbon, nitrogen,
hydrogen, sulfur
– fix nitrogen
– Clean oil spills
– Break down trash
Bacteria and Archaea
Some bacteria cause disease.
• by invading and
consuming tissues
or making toxins.
• A toxin is a poison
released by an
organism to slow
an immune response.
Bacteria and Archaea
Bacteria and Archaea
Bacteria and Archaea
Antibiotics are used to fight bacterial disease.
• Antibiotics destroy cell walls.
• Other antibiotics destroy the ribosomes of bacteria
• Many vaccines are also effective against bacterial
infections
• Antibiotics do not work on viruses.
Bacteria and Archaea
Archaebacteria vs. Eubacteria
• Believed to be the oldest life forms on the planet
• Are very different genetically from regular Eubacteria
(normal bacteria)
• Are found living in extreme environments
– Acidic Hot Springs
– Under Sea Volcanic Vents
– High Salt Water Areas
– Methanogens live in the gut of animals