Revised

Classification of Prokaryotes

• advances made with DNA sequencing

• use genes coding for ribosomal RNA (rRNA)

  • rRNA genes are ancient

  • almost all organisms have rRNA

  • necessary for translation

    • evolves slowly

• immense diversity, still mostly undescribed

Bacteria: Gram Negatives

• Thin peptidoglycan layer

• have an outer lipid membrane.

• 2 membranes (sandwhiched)

Proteobacteria (purple bacteria)

Gram Negative

• largest group of bacteria

• nutritionally diverse

Chlamydias

Gram Negative

• obligate intracellular lifestyle

• many animals parasites

• unusual cell wall

Spirochaetes

Gram Negative:

• Spiral-shaped

• Move by corkscrew motion

• many human pathogens

Cyanobacteria

Gram Negative

• photoautotrophs

• use chlorophyll a

• internal membrane system

• many also fix nitrogen

Bacteria: Gram-Positives

• have a thick peptidoglycan layer

• no outer lipid membrane

• 1 membrane and thick

Low-GC

gram positives

• low proportion of GC nucleotides

• Some produce endospores

• many disease causing

High-GC (actinobacteria)

gram positives

• high proportion of GC nucleotides

• form branched filaments

• many produce antibiotics

Diversity of Archaea

Archaea

• some extremophiles, but many live in “normal” habitats

• Many differences from both bacteria and Eukarya

Crenarchaeota

Archaea

• some thermophiles, some acidophiles, some both

• others important nitrifiers in ocean

Euryarchaeota

• some halophiles (salt lovers)

• Some methanogens — obligate anaerobes