Final answer:
The bacteria in question are obligate aerobes, which must have oxygen to grow and will therefore populate the surface of the liquid media where oxygen concentration is highest.
Step-by-step explanation:
The type of bacteria that grows at the top of the test tube because the most dissolved oxygen is located on the surface of a liquid media are known as obligate aerobes. These bacteria require an abundant supply of oxygen and cannot grow without it, as evidenced by their growth pattern in a test tube culture using a medium like thioglycolate.
Obligate aerobes are contrasted with other bacteria such as obligate anaerobes, which grow at the bottom of the tube and are killed by oxygen, and facultative anaerobes, which grow throughout the tube but thrive at the top. Facultative anaerobes can use oxygen but can also grow in its absence through fermentation or anaerobic respiration. Likewise, microaerophiles require low levels of oxygen, and aerotolerant anaerobes are indifferent to oxygen but do not use it for growth, while the obligate aerobes are completely dependent on oxygen for their metabolic processes.