Topic 9 The Ecology of Prokaryotes

1. Topic 9The Ecology of Prokaryotes Biology 1001 October 19, 2005

2. 4.3 Diversity of Metabolic Pathways • Nutritional Modes of Prokaryotes

3. 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 Alcohol fermentation Clostridium botulinum

4. 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

5. 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!

6. 9.3 Bacteria and Disease Lyme Disease – Borrelia burgdorferi • 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