Topic 9The Ecology of Prokaryotes

Biology 1001

October 19, 2005

4.3 Diversity of Metabolic Pathways Nutritional Modes of Prokaryotes

4.3 Diversity of Metabolic Pathways Oxygen metabolism

Obligate aerobes require O2 for cellular respiration for energy Facultative anaerobes use O2 if available but use fermentation in

an anaerobic environment Obligates anaerobes are poisoned by O2 and use either

fermentation or anaerobic respiration for energy

Clostridium botulinumAlcohol fermentation

9.2 Essential Ecological Roles Chemical Recycling

Chemoheterotrophs are decomposers, returning carbon and other nutrients to the soil

Cyanobacteria (photoautotrophs) produce O2 and convert CO2 to an organic form of carbon

Bacteria are important in the nitrogen cycle

Nitrogen fixing bacteria = N2 NH3

Ammonifying bacteria = organic N NH4

+

Nitrifying bacteria = NH4+ NO2

- or NO2

- NO3-

Denitrifying bacteria = NO3- N2

Figure 54.17

9.2 Essential Ecological Roles

Symbiotic Relationships “Metabolic cooperation” with other prokaryotes Symbiosis refers to an ecological relationship

between two organisms of different species in direct contact. In a symbiotic relationship with a eukaryote the prokaryote is the symbiont while the eukaryote is the host

Mutualism = both organisms benefit Commensalism = one benefits, the other is unharmed Parasitism = one benefits, the other is harmed Most relationships between humans and bacteria are

mutualistic!

9.3 Bacteria and Disease Pathogenic prokaryotes are parasitic to humans

Account for half of all human diseases

Cause illness by producing poisons, called toxins Exotoxins are proteins secreted by prokaryotes Endotoxins are components of the lipopolysaccharide outer membrane

of gram-negative bacteria Gram-negative bacteria tend to resist antibiotics because the outer

membrane impedes their entry

Clostridium botulinum

Endospore

Lyme Disease – Borrelia burgdorferi