Prokaryotes (Domains Bacteria & Archaea)

KEY POINTS 1.  Decomposers: recycle organic and

inorganic molecules in environment; makes them available to other organisms.

2.  Essential components of symbioses. 3.  Encompasses the origins of metabolism and

metabolic diversity. 4.  Origin of photosynthesis and formation of

atmospheric Oxygen

Animals

Colonization of land

Humans

Ceno- zoic

Origin of solar system and Earth

Prokaryotes Proterozoic Archaean

1 4

3 2

Multicellular eukaryotes

Single-celled eukaryotes

Atmospheric oxygen

ANTIQUITY

•  >3.5 BILLION years old.

•  Alone for 2 billion years

General characteristics 1.  Small: compare to

10-100µm for eukaryotic cell; single-celled; may form colonies.

2.  Lack membrane-enclosed organelles.

3.  Cell wall present, but different from plant cell wall.

General characteristics

4.  Occur everywhere, most numerous organisms.

–  More individuals in a handful of soil then there are people that have ever lived.

–  By far more individuals in our gut than eukaryotic cells that are actually us.

General characteristics

5.  Metabolic diversity established nutritional modes of eukaryotes.

General characteristics

6.  Important decomposers and recyclers

General characteristics

6.  Important decomposers and recyclers •  Form the basis of

global nutrient cycles.

General characteristics

7.   Symbionts!!!!!!! •  Parasites •  Pathogenic

organisms. •  About 1/2 of all

human diseases are caused by Bacteria

General characteristics

7.   Symbionts!!!!!!! •  Parasites •  Pathogenic

organisms. •  Extremely important

in agriculture as well.

Pierce’s disease is caused by Xylella fastidiosa, a Gamma Proteobacteria. It causes over $56 million in damage annually in California. That’s with $34 million spent to control it! = $90 million in California alone.

General characteristics

7.   Symbionts!!!!!!! •  Commensalists •  They are

everywhere (really). •  There can be 10

million cells per square centimeter of skin.

General characteristics

7.   Symbionts!!!!!!! •  Mutualists •  Eukaryotic life

would be impossible without this.

General characteristics 7.   Symbionts!!!!!!!

•  Mutualists •  Allows herbivorous

(plant-feeding) animals to digest cellulose and other low-quality plant tissues.

•  Termites •  Ungulates “chewing the

cud” •  Lagomorph coprophagy

General characteristics 7.   Symbionts!!!!!!!

•  Mutualists •  Mealybug endosymbionts

with endosymbionts.

General characteristics 7.  Symbionts!!!!!!!

•  Mutualists •  Komodo dragons and their “toxins”.

•  Hunt large prey and can inflict fairly minor wound.

•  Prey die fairly quickly from wound.

•  Infection by highly pathogenic Pasteurella multocida (Gamma Proteobacteria).

•  Prominent in saliva of dragons, but dragons have an anti-Pasteurella antibody.

TAXONOMY is problematic

•  Relationships obscured by billions of years of evolution

•  Also obscured by unique bacterial means of recombination (more later).

•  Grouped primarily by DNA sequence data.

•  Immense genetic/genomic diversity.

Current taxonomy is stabilizing

•  Note that “Prokaryote” is paraphyletic. Why?

•  Two Domains: •  Archaea: extremophiles

(mostly), ancient, probable progenitors of eukaryotes.

•  Bacteria: most commonly-encountered prokaryotes.

Characteristics

•  Cell Surface •  Motility •  Genome •  Reproduction & Growth •  Metabolic Diversity •  Nitrogen Metabolism •  Oxygen Relationships

Cell Surface

•  Archaea: plasma membrane of ether-lipids (unique in life).

•  Bacteria: a sugar polymer - peptidoglycan

Cell Surface •  Cell wall is often

modified with structures to adhere to substrate.

•  Many secrete a sticky capsule or adhere by fimbriae (ocasionally called pili).

Motility •  ~half the species can move. 1.  Flagella most common

(different structure from eukaryote)

2.  Spiral filaments: spirochetes corkscrew

3.  Gliding over slimy secretions (via flagellar motors without filament)

•  Capable of taxis (photo, chemo, geo, etc.)

Genome

•  Small genomes: ~1/1000th DNA content of eukaryotes.

•  No membrane enclosed nucleus.

•  DNA concentrated in ‘nucleoid’ region.

Genome •  One major chromosome,

double stranded DNA molecule in ring.

•  Sometimes several small DNA rings of few genes: plasmids. –  Replicate independently of

main chromosome. –  Permit recombination via

conjugation (later). –  Involved in resistance to

antibodies/antibiotics.

Genome

•  Broadly, replication & translation of genetic info like that of eukaryotes; differ in details and simplicity.

•  Used in first DNA recombinant research. •  Genetic recombination: Not like eukaryotes

(e.g. chiasma & crossing over)!! –  Transformation –  Conjugation –  Transduction

Genome: Recombination via transformation

•  DNA taken up from the environment

Genome: Recombination via conjugation

•  Direct transfer of DNA between cells.

•  Both plasmids and portions of bacterial chromosome.

Genome: Recombination via transduction

•  Transfer of DNA via phage viruses.

Reproduction & Growth •  Meiosis & Mitosis NOT

PRESENT. •  Asexual binary

fission. •  DNA replication can be

nearly continuous in ideal conditions (depends on pH, salinity, temperature, etc.)

•  Generation times as fast as 20 minutes

Metabolic Diversity

•  Nutrition: •  Requires a source of carbon for

synthesizing organic compounds: either carbon dioxide or living matter.

•  Requires a source of energy to drive reactions: either light or chemical.

Metabolism

Metabolic Diversity: Source of Carbon

•  AUTOTROPHS: Need only carbon dioxide (CO2) as carbon source

•  HETEROTROPHS: Need at least one organic nutrient as carbon source (e.g. glucose; petroleum)

•  Both of these present in domain Eucarya as well.

Metabolism

Metabolic Diversity: Source of Energy

•  PHOTOTROPHS: Need only sunlight as energy source

•  CHEMOTROPHS: Derive energy from oxidation of organic molecules.

•  Both of these present in domain Eucarya as well.

Metabolism

Metabolic Diversity: Combined

Which of these are present in multicellular Eucarya?

Metabolism

Energy Source:

Sun Environment

CO2 Photoautotroph Chemoautotroph

Organic molecules

Photoheterotroph Chemoheterotroph

Car

bon

Sou

rce:

Photoautotrophs

•  Use sun for energy, CO2 for carbon.

•  Photosynthetic bacteria (e.g. cyanobacteria).

•  Present in many plants and single-celled Eucarya

Metabolism

Chemoautotrophs •  Oxidize inorganics

(H2S, NH3) for energy. •  Need only CO2 as

carbon source. •  Unique to Bacteria and

Archaea. •  E.g. Methanococcus

jannaschii lives on hydrothermal vents at 2600m below sea level.

•  Reduces H2 + CO2 to CH4 + 2H2O.

Metabolism

Photoheterotrophs

•  Get enery from light but must obtain carbon in organic form (NOT CO2).

•  Unique to Bacteria and Archaea.

•  E.g. Halobacterium salinarium.

Metabolism

Chemoheterotrophs •  Consume organic

molecules for both energy and carbon.

•  Common among prokaryotes: –  saprobes

(decomposers) –  parasites (rely on

living hosts) •  Also widespread in

Protista, Animalia, Plantae.

Metabolism

Nitrogen metabolism •  Nitrogen fixation: •  The only* mechanism that

makes atmospheric Nitrogen available to other organisms.

•  Convert N2 into ammonia (NH3) which is quickly protonated into ammonium (NH4

+). •  Essential for multicellular

life!

Metabolism

Oxygen Relationships •  Aerobic vs. Anaerobic •  Obligate aerobes: use O2 for

cellular respiration. •  Facultative anaerobes: use

O2 if it is present by carry out anaerobic respiration or fermentation in anaerobic environment.

•  Obligate anaerobes: poisoned by O2; use anaerobic respiration or fermentation.

•  Cellular respiration: –  Carbohydrates + O2 →CO2

+ H2O + energy •  Fermentation:

–  Carbohydrates →CO2 + ethanol + energy

•  Anaerobic respiration: –  Carbohydrates + [X] →

bicarbonate + [X-] + energy –  Where [X] is a substance

other than O2 that accepts electrons such as nitrates or sulfates

Oxygen Relationships

•  Early life (during the Archaean) was primarily anaerobic.

•  Evolution of photosynthesis in Cyanobacteria changed all this.

Taxonomy of Prokaryotes •  Archaea or Archaebacteria

–  Methanogens –  Halophiles –  Thermophiles

•  Bacteria or Eubacteria –  Protobacteria –  Chlamyidias –  Spirochetes –  Cyanobacteria –  Gram-positive bacteria

Archaea or Archaebacteria •  Live in extreme

environments (extremophiles): sulfur hot springs, deep sea vents, high salt environments.

•  Lack peptidoglycan, unique plasma membrane of liquids

•  Likely sister group of Eukaryotes

Archaea or Archaebacteria

•  Methanogens –  Use H2 to reduce

CO2 to methane (CH4).

–  Chemoautotrophs –  Anaerobic –  In swamps, marshes,

deep sea vents, important decomposers.

Archaea or Archaebacteria

•  Halophiles –  Saline environments. –  Salinity several times

higher than sea water.

–  Photoheterotrophs

Archaea or Archaebacteria

•  Thermophiles –  60º-80ºCpH 2-4

optimal –  Chemoautotrophs –  Oxidize HS

Bacteria or Eubacteria

•  Grouped by molecular systematics.

Bacteria or Eubacteria

Proteobacteria •  VERY diverse, grouped

into five taxa based on DNA sequence data.

•  Includes most types of metabolism that we’ve discussed.

•  Includes most of the types of symbioses we’ve discussed

•  Review the summary in Figure 27.16.

Bacteria or Eubacteria Gram positive Bacteria: •  Simple peptidoglycan cell wall. •  Rival Proteobacteria in

diversity. •  Most are free-living

decomposers. •  Some pathogenic (e.g. strains

of Staphylococcus, Streptococcus, Bacillus anthracis, Clostridium botulinum).

•  Include the mycoplasms--the only bacteria that lack cell walls

Bacteria or Eubacteria Cyanobacteria:

•  Photoautotrophs •  Only prokaryotes with

plant-like, O2-generating photosynthesis.

•  Present in freshwater and marine environments.

•  Often colonial--first steps toward multicellularity?

Bacteria or Eubacteria

Spirochetes: •  Helical •  Recall motility: move by

means of rotating, internal, flagellum-like filaments.

•  Free-living and parasitic.

•  Chemoheterotrophs (like us).

Bacteria or Eubacteria

Chlamydias: •  ALL are parasites of

animals. •  Intercellular. •  Lack peptidoglycan in

the cell wall (are they gram-positive or gram-negative?).

•  Most common form of STD in USA (urethritis).

Prokaryotes: Summary

•  You should now have a good sense of prokaryote biology and diversity.

•  Including roles in metabolism, symbioses, global energy cycles.

•  Important distinguishing characteristics of cell wall, motility, genome, replication.

•  General aspects of their systematics.