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Microbiology · Chapter 6

Oxygen & the Thioglycollate Tube

A single tube of reduced broth — oxygen-rich pink at the top, oxygen-free at the bottom — sorts bacteria by the one thing they can and can't live with. Tap each class to see where it grows and why.

The thioglycollate tube

O₂ high aerobic less O₂ no O₂ anaerobic
Sodium thioglycolate scrubs out oxygen; a splash of resazurin dye stays pink where O₂ remains (top) and colorless once reduced (below). Bacteria multiply into visible cloudiness only at the depth their metabolism allows.
Five oxygen classestap one to read the tube
Why the band appears where it doesGrowth needs two things: a usable energy pathway and defenses against oxygen's toxic byproducts — superoxide and hydrogen peroxide. Enzymes superoxide dismutase (SOD) and catalase neutralize them. Which enzymes a microbe carries decides how close to the pink it can survive.