Topic 9 The 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 O 2 for cellular respiration for energy  Facultative anaerobes use O 2 if available but use fermentation in an anaerobic environment  Obligates anaerobes are poisoned by O 2 and use either fermentation or anaerobic respiration for energy Clostridium botulinum Alcohol fermentation

9.2 Essential Ecological Roles Chemical Recycling  Chemoheterotrophs are decomposers, returning carbon and other nutrients to the soil  Cyanobacteria (photoautotrophs) produce O 2 and convert CO 2 to an organic form of carbon  Bacteria are important in the nitrogen cycle Nitrogen fixing bacteria = N 2  NH 3 Ammonifying bacteria = organic N  NH 4 + Nitrifying bacteria = NH 4 +  NO 2 - or NO 2 -  NO 3 - Denitrifying bacteria = NO 3 -  N 2 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