Thioglycolate broth is a medium used mainly to find out the oxygen requirements of microorganisms.
1: Obligate aerobes need oxygen. They gather at the top of the tube where its concentration is highest.
2: Obligate anaerobes are poisoned by oxygen, so they gather at the bottom of the tube where the oxygen concentration is lowest.
3: Facultative anaerobes can grow anywhere in tube, but they gather mostly at the top because they have more energy with oxygen.
4: Microaerophiles need oxygen: they cannot ferment or respire anaerobically. However, they are poisoned by high concentrations of oxygen. They gather in the upper part of the test tube but not the very top.
5: Aerotolerant organisms do not need oxygen as they metabolise energy anaerobically. But, unlike obligate anaerobes, they are not poisoned by oxygen. They are found evenly spread throughout the test tube