Chapter 27
Prokaryotes and the Origins of
Metabolic Diversity
Prokaryotes are (Almost) Everywhere!
• Their biomass outweighs all eukaryotes by at
least 10 times
• More inhabit the mouth of a human than the
total number of people that ever lived
Loners or Groupies?
• Most prokaryotes are unicellular
• Some species aggregate transiently in groups
of two or more cells
• In some, there is a division of labor between
two or more specialized types of cells
Shapes and Sizes
• Spheres (cocci)
• Rods (bacilli)
• Helices (spirilla and spirochetes)
• Diameters are 1-5 nanometers… up to 0.75
mm
Cell Walls
• Nearly all prokaryotes have a cell wall external
to the plasma membrane
• Made of peptidoglycan, not cellulose
• Gram Stain– Gram + = have simple walls with a lot of
peptidoglycan, stain purple
– Gram - = more complex walls with less
peptidoglycan, stain pink
Watch Out! Here Comes a Gram –
Bacteria!!!
• Gram – bacteria are more threatening
– The lipopolysaccharides on the walls are toxic
• Excess killing of these bacteria can lead to shock
– More resistant to antibiotics because outer
membrane impedes drug entry
You’d Better Clock That Guy…
• Half of prokaryotes are capable of directional
movement
• Some exceed speeds of 50 nanometers /
second
– ~ 100 times their body length per second
• Flagella
• Slimy film
• Taxis: movement toward or away from stimuli
Pro vs. Eu
• Pro:
– Lack true nuclei enclosed by membranes
– Smaller, simpler genomes
• 1/1000th as much DNA as Eukaryotes
• DNA concentrated in nucleoid region
• DNA is in RINGS, not helixes
– Plasmids- smaller rings of DNA consisting of a few genes
Populations Grow and Adapt Rapidly
• Binary fission- asexual cell division
• Mechanisms for gene transfer
– Transformation
• Takes up cells from the environment
– Conjugation
• Direct transfer of genes
– Transduction
• Viruses transfer genes between prokaryotes
• Mutation is the major source of genetic variation
Growth Can Be Exponential
• If resources are good, growth can be
enormous
• Some have generation times of 1-3 hours, but
can double every 20 minutes in perfect
environment
– If growth were exponential and not stopped, one
cell can give rise to a colony outweighing Earth in
just three days!
– Ex: HeLa Cells
HeLa Cells
• Henrietta Lacks: black tobacco farmer from
Virginia who died of cervical cancer at 30
• First IMMORTAL cells ever grown in lab
– Essential to developing polio vaccine
– Went up in the first space shuttle to see what
happens to cells in zero gravity
– Have continued to grow and divide for 60 years in
vitro
Survival of the Fittest
• Some prokaryotes form endospores, which are
resistant to harsh conditions
• Have to kill them by superheating
– Autoclaves operate at 120 degrees C
• Can remain dormant for centuries, and can
revive to the original state in perfect
conditions
• Some release antibiotics to decrease the
competition it has to face
Photoautotrophs
• Photosynthetic that harness light to drive
synthesis of organic compounds from CO2
• Ex: Cyanobacteria
– All eukaryotic plants and algae
Chemoautotrophs
• Only need CO2 as a carbon source
• Obtain energy by oxidizing inorganic
substances
– Hydrogen sulfide, ammonia, etc
• Can extract energy by oxidizing minerals in
stone and are currently “eating away” at some
of the world’s greatest statues
Photoheterotrophs
• Use light to generate ATP
• Must obtain their carbon in organic form
Chemoheterotrophs
• Must consume organic molecules for both
energy and carbon
• Protists, fungi, animals, parasitic plants
Nutritional Diversity Among
Chemoheterotrophs
• Saprobes- decomposers that absorb their
nutrients from dead organic matter
• Parasites- absorb nutrients from the body fluids
of living hosts
• Some have specific requirements:
– Lactobacillus will grow only in a medium containing all
20 amino acids, several vitamins, and other organic
compounds
• Some have less specific requirements:
– E. coli only needs glucose to grow
Nitrogen Metabolism
• Prokaryotes are the only ones that cycle
nitrogen through the ecosystem
• Nitrogen fixation is the only biological
mechanism that makes atmospheric nitrogen
available to organisms for incorporation into
organic compounds
It’s All About the O
• Obligate aerobes: use O2 for cellular
respiration and cannot grow without it
• Facultative anaerobes: use O2 if it is present
but can grow by fermentation in an anaerobic
environment
• Obligate anaerobes: poisoned by O2
Extremeophiles
• Loves extreme conditions
– Hot water of geysers
• Methanogens- use CO2 to oxidize H2, and
produce methane as a waste product
• Live in swamps or marshes where there is NO O2
• Important decomposers in sewage treatment
• Extreme Halophiles- live in high saline solutions
– Great Salt Lake and Dead Sea
• Extreme Thermophiles- thrive in hot
environments
– Deep sea hydrothermal vents
Ecological Importance of Prokaryotes
• Indispensable links in the recycling of chemical
elements in ecosystems
• Many are symbiotic
– Mutualism: both benefit
– Commensalism: one receives benefit but the
other is not harmed
– Parasitism: one receives benefit at the detriment
of the host
Ecological Importance of Prokaryotes
• Cause many human diseases
– Koch’s Postulates
• Find same pathogen in each diseased individual
• Isolate the pathogen from diseased subject and grow in
pure culture
• Induce the disease by transmitting pathogen
• Isolate the same pathogen from new group as old one
• Research and technology