Prokaryotes & the Origins of Metabolic Diversity

Chapter 27

The Three Domains of Life

A Comparison of the Three Domains of Life

Structure & Function:Common Shapes

Structure & Function:Cell Wall

• Most have cell wall– Maintains shape– Protection

• Made of peptidoglycan

• Gram Stain: Identifies bacteria by cell wall– Gram positive

• simple cell wall

– Gram negative (more dangerous)• More complex

• Less peptidoglycan

Gram-positive and gram-negative bacteria

Gram-positive and gram-negative bacteria

Structure & Function:Motility

Structure & Function:Pili

Structure & Function: Endospores

Structure & Function: Specialized Membranes

Cyanobacteria

Contrasting hypotheses for the taxonomic distribution of photosynthesis among prokaryotes

Nutritional Diversity: Chemoheterotrophs

• Saprobes– Decomposers that absorb nutrients from dead

organic matter

• Parasites– Absorb nutrients from body fluids of living host

Nutritional Diversity:Nitrogen metabolism

• Nitrogen fixation – – Conversion of N2 to ammonium– Many bacteria can do it

• Other bacteria can convert– Ammonium to nitrate– Nitrate to N2

• Remember the nitrogen cycle?

Nutritional Diversity:Oxygen

• Obligate aerobes – cannot grow w/out oxygen

• Obligate anaerobes – poisoned by oxygen

• Facultative anaerobes – will use oxygen if it is there, but can live w/out it

Archaea:Extremophiles

• Methanogens– Produce methane as waste– Obligate anaerobes– Live in swamps and marshes– Used as decomposers in waste water

treatment plants– In guts of animals that digest a lot of cellulose

• Extreme halophiles

– Salt lovers

– Some require high salinity

– bacteriorhodopsin

Archaea:Extremophiles

Archaea: Extremophiles

• Extreme Thermophiles– 60-80 degrees Celsius

– Some obtain energy by oxidizing sulfur

– Found in hot springs and deep-sea hydrothermal vents