Prokaryotes
• Lack nuclei
• Typically lack or have very few internal
membranes
• Cytoplasm contains ribosomes, storage
granules that hold glycogen, lipid, or
phosphate compounds
• Metabolic enzymes are associated with the
plasma membrane, especially where it is
infolded to form limited internal membranes –
such membranes are generally referred to as a
mesosome
• The plasma membrane interacts with the
cytoplasm in signaling functions
• Motile bacteria have a corkscrew flagellum
Prokaryotic Organization
• Key features
– No nucleus
– DNA held in nucleoid
– Cytoplasm dense:
• Ribosomes
• Storage granules
• Limited membranes
– Plasma membrane
– Corkscrew flagellum
– Cell wall is complex
•
•
•
•
Outer membrane
Peptidoglycan layer
Capsule
Pili extend from
cytoplasm
Domains of Life
BACTERIA
• ARCHAEBACTERIA
– Introns in DNA
– Lack peptidogycan in
cell walls
– Live in extreme
environments
• EUBACTERIA
– Includes most
bacteria
– Most have one of
three shapes
– May be divided into
up to 12 phyla
– Classification is
controversial
Archaebacteria and Eubacteria
• Carl Woese has indicated, based on small
subunit ribosomal RNA (SSU rRNA) sequencing,
that there are two domains of bacteria
• Archaea
–
–
–
–
–
Lack peptidoglycan in cell wall
Produce methane gas
Ether-linked lipids
Live in ‘early Earth’ conditions
Extreme halophiles, thermophiles, and acidophiles
• Eubacteria
– Have peptidoglycan in cell wall
– Are rifamycin-sensitive (blocks transcription)
– All other bacteria
TYPES OF ARCHAEBACTERIA
Methanogens
living in sewage
Thermoacidophilies
Living in hot springs
Extreme halophile
living in the Great Salt Lake
The Archaea
• Methanogens
– Anaerobes
– In digestive tracts of animals
– Produce methane gas
• Extreme halophiles
– Live in saturated salt
– Many are photosynthetic
• Extreme thermophiles
– Live in hot springs
– Often live in acidic environments (acidophiles)
The Eubacteria
• Most abundant bacteria
• Important in the biosphere
– Major producer of primary production (of
carbon via photosythesis)
– Most numerous organisms in the soil
– Most important nitrogen fixing organisms,
often via symbiotic associations
• e.g. rhizobial bacteria in root nodules
Bacteria
• Bacteria are prokaryotes
– They are cells
– They lack nuclei
• There are two professional viewpoints
regarding the general, overall classification
of prokaryotes:
– Some biologists support the concept that they
constitute two domains: Archaea and
Eubacteria
– Other biologists classify them into two
kingdoms, Archaebacteria and Eubacteria
• Most are very small – 0.5 – 1.0 mm in
diameter
BASIC SHAPES OF EUBACTERIA
ROD-SHAPED
SPHERICAL
SPIRILLA
Cell Walls
• Provides support for cell
• Protects against osmotic shock
– Most bacteria well adapted to hypotonic conditions
– Most bacteria grow poorly in hypertonic conditions;
hence jams, salted foods prevent bacterial growth
• Cell wall composition unique to bacteria
– Eubacterial cell wall made of peptidoglycan
• Complex of polymerized amino sugars and short
polypeptides
• Is really one polymer surrounding the cell
Capsules and Pili
• Many bacteria secrete a capsule, or
slime layer
– Used to attach, prevent phagocytosis
– Can be used to enhance infective bacteria
• Pili are hair-like appendages
– Allow attachment to surfaces
– Are sometimes involved in bacterial
conjugation (sexual activity that involves
the transfer of DNA)
The Bacterial Flagellum
• Rotates
• Is corkscrew-shaped
• Three parts:
– Basal body
– Hook
– Filament (made of one
protein: flagellin)
• Cell uses ATP to pump
protons out
• Protons diffuse through
membrane at basal body
• Breakdown of gradient
converted to rotation
The Gram Stain
• Bacterial cell wall differences can be used to
identify and categorize cells
• 1888: Christian Gram developed the Gram Stain
– Some bacteria retain crystal violet stain after alcohol
wash
• Called gram-positive
– Other cells referred to as gram-negative
• Stain retention determined by cell wall
organization
– Gram-positive cells have thick peptidoglycan wall
– Gram-negative cells have outer membrane and thin
peptidoglycan layer
Gram-positive and Gram-negative Cell Walls
Most Species of Eubacteria may be
Grouped Based on Staining
• Gram-Negative
– Lack thicker layer of
peptidoglycan
– Stain pink
– Endotoxins
• Gram-Positive
– Thicker layer of
peptidogycan
– Stain purple
– Exotoxins (released
when bacteria die)
Gram-positive
Gram- negative
Giant Bacterium
• But size is not an indicator; Epulopiscium
fishelsoni is a giant bacterium from the gut of
the surgeonfish
• Here, ~ 600 mm long and 80 mm wide, much
larger than the large protist Paramecium
(other cells in picture)
Nutrition and Growth
•
•
•
•
•
•
Saprophtes
ex: decomposers
Photoautotrophs
ex: blue-green algae
Obligate anaerobes ex: tetanus
Facultative anaerobes
ex: E.Coli
Obligate aerobes
ex: tuberculosis
Thermophilic bacteria
Most bacteria grow at at neutral pH but some
grow best at a pH of 6 or lower
– Bacteria that produce yogurt and sour cream
Anabaena: a Eubacterium
• Complex, free-living & photosynthetic
• A cyanobacterium
• The larger cells fix nitrogen, are
oxygen-sensitive
Bacterial Chromosome
• Bacteria have a circular genomic DNA
molecule – Single chromosome
– ~1000X longer than cell if stretched out
• Also have plasmids
– Small, circular DNA fragments
– Can replicate independently of the genomic
DNA or be integrated into genomic DNA
– Carry genes for resistance, for genetic
exchange or for enzymes
Bacterial Sexual Reproduction
• Most simply put, sex is transfer of genetic
information.
• Three mechanisms known for bacterial sexual
reproduction:
– Transformation
• Bacteria take up DNA from environment
• Griffith’s 1928 experiment with S and R bacteria showed
that DNA was heritable substance
– Transduction
• Genes are transferred through phage (next slide)
– Conjugation
• Two cells of opposite mating type come together, form pili
bridges bridges through which DNA is transferred
Conjugation of E. coli
Bacterial Pathogens
• Some are disease-causing agents
– Most bacteria are not harmful
– Many have positive relationship with hosts
– e.g. human gut microbe E. coli
– But many are pathogenic
– Cause serious disease:
• Cholera
• Diphtheria
• Tuberculosis
Antibiotics
• Antibiotics are drugs that combat
bacteria by interfering with cellular
functions
– Penicillin – interferes with cell wall
production
– Tetracycline – interferes with protein
production
– Sulfa drugs – produced in the laboratory
– Broad-spectrum antibiotics will affect a
wide variety of organisms
Endotoxins
• Pathogenic bacteria can produce exotoxins,
which increase their success but tend to be very
damaging to the host
– Often the toxin, not the bacterial infection, is most
dangerous
– Examples:
• Diphtheria toxin
• Botulism toxin
• Endotoxins:
– Not secreted but are components of the cell wall
– Affect host when released from dead bacteria
– Can bind macrophage, cause the release of feverinducing agents
– Resistant to heating
Commercial Bacteria
• Bacteria used in many commercial processes
– Lactic acid bacteria convert lactic acid to simpler
monomers
• Used in yogurt, acidophilous milk for lactose-intolerant people
– Bacteria used for making
• Cheeses
• Fermented meats such as salami
• Pickling agents such as vinegar
– Bacteria also used to make pharmaceutical agents
– Also used as means to make biomedical agents and
biological molecules
– Used also to reduce pollution – as bioremediation
agents
Penicillin
• This amazing fungus
produces the famous
antibiotic, penicillin. In
1928. Alexander Fleming
observed that a mold called
Penicillium notatum
produced a substance, later
known as penicillin, that
killed bacteria in its
presence. This antibiotic
This fungus makes antibiotics and
was the first of many to be
cheese. Other varieties of the
found and used to treat
fungus produce blue cheese and
infections.
Roquefort cheeses.
• Interferes with cell wall
production.
Koch’s Postulates
• Robert Koch, late 19th Century
• Defined conditions likely to identify a
pathogen
1. Present in all infected individuals
2. Sample of the micro organism can be
grown in culture from the host
3. Culture produces disease in a second host
4. Microorganism can be recovered from
second, experimentally created host