Final answer:
The physiological oxygen requirement of a bacterium is determined by observing its growth on different media under varying oxygen conditions and performing metabolic tests. These observations help categorize the bacterium as a strict aerobe, strict anaerobe, facultative anaerobe, microaerophile, or aerotolerant anaerobe.
Step-by-step explanation:
To determine the physiological oxygen requirement for a bacterium, one must observe the bacterium's growth patterns under different oxygen conditions. For instance, strict aerobes require a constant supply of oxygen and will only grow in oxygen-rich environments, as seen in the growth pattern at the top of a thioglycolate tube.
Observing growth on agar plates, whether incubated aerobically or anaerobically, provides insights into a bacterium's oxygen growth requirement category. For example, growth on blood agar aerobically indicates an aerobe or facultative anaerobe, while growth on blood agar incubated anaerobically suggests an anaerobe or facultative anaerobe.