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Microbiology · Chapter 4

Bacteria & Oxygen

Grow bacteria in a tube of thioglycollate broth and oxygen sorts them out for you: O₂ is richest at the surface and vanishes toward the bottom. Where a species chooses to grow reveals exactly how it handles oxygen. Tap each group to see its pattern.

Obligate aerobe

high O₂ (~21%, air) no O₂ (anaerobic)
Fluid thioglycollate tube · oxygen diffuses in at the top and is used up toward the bottom
Five ways to meet oxygentap a group to see where it grows
Why oxygen can be lethal: using O₂ generates toxic superoxide and hydrogen peroxide. The enzymes superoxide dismutase (SOD) and catalase detoxify them — bacteria that lack these defenses are damaged or killed by air.