Early Life and Diversification of Prokaryotes

Unique Characteristics of Bacteria

• No membranous nucleus - only a nucleoid region

• Circular DNA which obeys classic pairing rules

• No membrane bound organelles

• Contain ribosomes that differ in size from eukaryotes

• Some have endospores

  • resistant cells that develop when water or nutrients are lacking

  • dormant and can remain viable and survive for centuries in extreme conditions

• Often form biofilms

• Some have endospores

• Some have capsules

• Some have flagella - different from eukaryotes

Most Common Shapes

• Cocci (spherical)

• Bacilli (rods)

• Spirals

History

• Van Leeuwenhoek may have seen first prokaryotes with the microscope

• Koch’s postulates

  1. Microbe must be present in all cases of the disease

  2. Microbe can be isolated and grown in pure culture

  3. Microbe must cause the disease when inoculated into a healthy host

  4. Microbe must be re-isolated from the newly infected host

Gram Positive (+)

• Violet dye, darker color

• Simpler cell walls

• Thick layer of peptidoglycan

  • network of modified sugars and polypeptides

Gram Negative (-)

• Red dye, lighter color

• Less peptidoglycan

• Outer membrane with lipopolysaccharides

• Lipid portions of polysaccharides can be toxic

Major Nutritional Modes

• Photoautotroph

• Chemoautotroph

• Photoheterotroph

• Chemoheterotroph

Transformation

• Prokaryotic cells alter their genotype with DNA taken up from the external environment

Transduction

• Phages move prokaryotic genes from one host cell to another

Plasmids

Obligate Aerobes

• Requires oxygen to grow

  • Aerobic respiration

Obligate Anaerobes

• Can’t tolerate oxygen

  • anaerobic respiration

Nitrogen Fixation

• Some prokaryotes use nitrogen fixation to convert atmospheric N2 to ammonia (NH3) that can be used by prokaryotes

Metabolic Cooperation

• Cooperation between different prokaryotic species can create surface-coating colonies (biofilms)

• Can cause infections, tooth decay, contamination of medical devices

F factor

• F factor is a piece of DNA consisting of 25 genes required for the production of pili

• May be present in the chromosome of an F plasmid

• In conjugation, F+ plasmid donate DNA, F- plasmid receive DNA

• Transfer of F plasmid converts an F- cell to a recombinant F+ cell.

Conjugation

• Process where genetic material is transferred directly between prokaryotic cells

• DNA transfer is one way in bacteria

• ex. E. Coli, donor cell attaches to a recipient by a pilus, pulls it closer, and transfers DNA

Lineages: Protobacteria (All Gram Negative)

1. Subgroup alpha protobacteria

   a. Rhizobium - lives in root nodules of legumes and fixes atmospheric N2

2. Subgroup beta protobacteria

   a. Nitrosomas - converts NH4 to NO2

3. Subgroup gamma protobacteria

   a. Legionella, Salmonella, Vibrio, Eschericia Coli (in the gut of mammals)

4. Subgroup delta protobacteria

   a. Myxobacteria - produces a fruiting body

5. Subgroup epsilon

   a. Campylobacter, Helicobacter

Lineages: Chlamydia (Gram Negative)

1. Chlamydia trachomatis blindness and urethritis

   a. most common STD in the US

Lineages: Spirochetes (Gram Negative)

1. Treponema pallidum - syphilis

2. Borrelia burgdorferi - Lyme disease

Lineages: Cyanobacteria (Gram Negative)

• Photosynthetic

• May be solitary or filamentous

Lineages: Gram Positive Bacteria

• Actinomycetes - important in soils

• Clostridium Botulinum

• Staphylococcus aureus

• Streptococcus pneumonia

Lineages: Archaea

1. Extreme Halophiles - live in high salt concentrations

2. Extreme Thermophiles - live in high temperature