Prokaryotes and the Origins of
Metabolic Diversity
Unique Characteristics and
Success on Earth
• Found everywhere …
ubiquitous!
• Unicellular
• One chromosome which is
circular
• Lack membrane enclosed
organelles
• Asexual … binary fission
• Smaller ribosomes
• Small (1-5µm)
• Huge diversity
• Most ancient life
• Live in extreme environments
Impact on Biological Ecosystems
• Decompose dead matter
• Cycle Carbon, Nitrogen from
organic material to soil and
atmosphere.
• Lakes, rivers, oceans …
return chemical elements as
inorganic compounds that
can be used by plants.
• Symbiotic relationships
– Intestines – Vitamins
– Mouth – kill fungi
– Mitochondria and
chloroplasts evolve from
prokaryotes that are
residents in host cells
3 Domain System
• 2 major groups of
prokaryotes
• Archaea
– “ancient”
– Extreme habitats
– Share some
similarities with
Eukaryotes
• Bacteria
– Common
prokaryotes we
encounter
Size, Organization, Specialization
•
•
•
•
Mostly unicellular
Cocci, Bacilli, Helical
1-5 µm
Some prokaryotes
will specialize and
create a division of
labor
– Nitrogen fixation
– Anti-fungal
Structure, Composition, and
Function of Cell Walls
• Maintains Shape
• Physical Protection
• Prevents Bursting in
Hypotonic Solution
• Peptidogylcan – sugars
cross-linked by
polypeptides (not in
Archaea)
• Gram+ = simpler wall w/
lots of peptidoglycan
• Gram- = more complex
w/ lipopolysaccharids but
w/ less peptidoglycan
Gram Stain and Disease
• Gram+
– Peptidoglycan traps the crystal violet
– Stains blue/purple
• Gram– Less peptidoclycan, crystal violet easily rinsed away
but safranin dye is retained
– Stains pink
– Lipopolysaccharides are often toxic
– Outer membrane helps defend against host and
antibiotics (prevent cross link in peptidoglycan)
Motility and Flagella
•
•
½ of prokaryotes are capable of
movement (some 100 X body /
second)
Flagella
– Smaller than eukaryotes, not
covered by membrane
– Filaments rotate and cell is
propelled
– Powered by diffusion of H+ ions
•
Spirochetes
– Helical filaments; corkscrew
movement
•
Gliding (Slime)
– Filamentous chains secrete slime
for gliding
•
Chemotaxis
– Postive or negative
•
Phototaxis
Prokaryotic Genome
• No “true” nuclei
• Small, simple genome
• 1/1000th as much DNA as
a eukaryote
• Nucleoid Region
– Double stranded DNA in from of a
ring
– Plasmids
– Smaller rings of DNA
• Smaller ribosomes
– Tetracyline and
chloramphenicol bind to
ribosomes and block protein
synthesis
Genetic Variation
• Transformation
– Genes taken in from
surrounding environment
• Conjugation
– Genes exchanged between
bacteria (direct)
• Transduction
– Genes transferred via a virus
• Mutation
– Random change in DNA
sequence due to replication
error
– Most common source of
variation
Bacterial Growth
• Multiplication of cells and increase in
population size
• NOT enlargement of individual cells
• Conditions for optimal growth will vary
– Temp, pH, salts, nutrients
• Refrigeration
– Slows the growth of microorganisms
• Geometric Growth
– 20 minutes – 3 hours
– Colony outweigh Earth in 3 days
Endospores
• Resistant Cells
• Replication of
chromosome which is
surrounded by a
durable wall
• Allows for protection in
harsh conditions
• May lie dormant for
centuries (250 my)
• Food-canning industry
must take precautions
Antibiotics
• Inhibit the growth of
microorganisms
• Prokaryotes must
compete for space
and nutrients
• Defense against
other bacteria or
protists and fungi
Zone of Inhibition
Obtaining Energy and Carbon
Mode of
Nutrition
Photoautotroph
Chemoautotroph
Energy
Source
Light
Carbon
Source
CO2
Inorganic CO2
chemicals
PhotoLight
heterotroph
ChemoOrganic
heterotroph compounds
Organic
compounds
Organic
compounds
Types of
Organisms
Cyanobacteria,
plants
Prokaryotes
Sulfolobus
Prokaryotes
Prokaryotes
Protists, fungi,
animals
Diversity among Chemohetertrophs
• Saprobes
– Decomposer that absorb their nutrients from dead
organic matter
• Parasites
– Absorb nutrients from the body fluids of living hosts
• Almost any organic molecule can serve as
food for at least some species. (petroleum)
• Nonbiodegradable
– Cannot be broken down by chemoheterotrophs
Nitrogen Fixation
• Nitrogen is an essential part of
proteins and nucleic acids
• Prokaryotes are able to
metabolize most nitrogenous
compounds
• Convert ammonium (NH4+) to
Nitrite (NO2-)
• “Denitrify” = Nitrate (NO3-) to
N2 (gas)
• Nitrogen fixation
– N2 (gas) to ammonium (NH4+)
– Only biological mechanism
that converts atmospheric
nitrogen available to
incorporate into organic
material
Metabolic Relationships to Oxygen
• Obligate aerobes
– Use oxygen for cellular respiration and cannot grow
without it
• Facultative anaerobes
– Uses oxygen if present but can also grow by
fermentation (anaerobic)
• Obligate anaerobes
– Poisoned by oxygen
– Fermentation
– Anaerobic respiration (inorganic molecules accept
electrons at the “downhill” end of ETC)
Evolution of Metabolic Diversity
• Glycolysis
– Heterotrophic bacteria use
the organic material in the
“primordial soup”
– Depleted supply of organic
material
• Bacteria that can harness
the energy from sunlight
and carbon dioxide are
favored
• Electron Transport Chains
Develop
• Photosynthesis
• Cellular Respiration
Moneran Classification
• Molecular Systematics
– Signature sequences of
small-subunit ribosomal
RNA (SSU-rRNA)
– Create history of earliest
prokaryotes to modern life
• Clinical Phenotypes
– Useful for identification
– Poor for phylogeny
– Nutritional modes are
scattered around the
phylogenetic tree
Extremophiles
• Methanogens
–
–
–
–
Use carbon dioxide to oxidize hydrogen
Produces methane (CH4)
Anaerboes
Found in swamps, marshes, sewers, guts of animals
• Extreme halophiles
– “salt lovers”
– Found in the Great Salt Lake and Dead Sea
• Extreme thermophiles
– Thrive in hot environments
– Optimal temperature is usually 60-80oC
Recycling
• Atoms of the organic materials in our bodies
were once part of the inorganic compounds in
the soil, air, and water.
• Bacteria act as decomposers.
– Return carbon, nitrogen, etc. from organic material
and waste products.
Relationships
• Symbiosis
– “living together”
• Mutualism
– Both organisms benefit
– Ex: bacteria in root nodules of beans (fix nitrogen)
• Commensalism
– One organisms benefits, while the other is not harmed or helped
– Ex: bacteria on the outer surfaces of the body
• Parasitism
– One organism benefits (parasite) at the expense of the other
– Ex: pathogens – cause disease in the host
Koch’s Postulates
• The organism must be found in all animals
suffering from the disease, but not in healthy
animals
• The organism must be isolated from a diseased
animal and grown in pure culture.
• The cultured organism should cause disease
when introduced into a healthy animal.
• The organism must be reisolated from the
experimentally infected animal.
Exotoxins vs. Endtoxins
• Exotoxins
– Proteins secreted by prokaryotes
– Can produce disease even w/o bacteria
– Ex: Clostridium botulinum – 1 gram of botulism can
kill 1 million people
– Ex: Vibrio cholerae – causes cholera, which is
characterized by severe diarrhea
• Endotoxins
– Components of outer membranes of Gram- bacteria
– Ex: Salmonella typhi – causes typhoid fever
Streptomyces
• Soil bacteria responsible for many
antibiotics including
– Streptomycin, neomycin, erythromycin,
aureomycin and tetracyclin
• Used to produce recombinant human
proteins
• Derived the anti-fungal drug nystatin
Limitations of Antibiotics
• Rapid evolution of antibiotic-resistant strains of
pathogenic bacteria.
• Biological Weapons
– Vlad III the Impaler
– Native Americans decimated with Old World diseases
– Diseases considered for weaponization, or known to be
weaponized include anthrax, Ebola, Bubonic Plague, Cholera,
Tularemia, Brucellosis, Q fever, Machupo, Coccidioides mycosis,
Glanders, Melioidosis, Shigella, Rocky Mountain Spotted Fever,
Typhus, Psittacosis, Yellow Fever, Japanese B Encephalitis, Rift
Valley Fever, and Smallpox. Naturally-occurring toxins that can
be used as weapons include Ricin, SEB, Botulism toxin,
Saxitoxin, and many Mycotoxins. The organisms causing these
diseases are known as select agents. Their possession, use,
and transfer are regulated by the Centers for Disease Control
and Prevention's Select Agent Program.
Exploitation of Prokaryotes