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

Prokaryotes

Protists, fungi, animals

Organiccompounds

Organiccompounds

Chemo-heterotroph

ProkaryotesOrganiccompounds

LightPhoto-heterotroph

Prokaryotes

SulfolobusCO2Inorganic

chemicalsChemo-autotroph

Cyanobacteria, plants

CO2LightPhoto-autotroph

Types of Organisms

Carbon Source

Energy Source

Mode of Nutrition

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