Which microorganisms require free dissolved oxygen for their metabolic processes?

Microorganisms that require free dissolved oxygen for their metabolic processes are known as aerobes. These organisms rely on aerobic respiration to generate energy, which is a process that utilizes oxygen to break down organic compounds efficiently. Aerobes thrive in environments where oxygen concentration is sufficient because they use it as the final electron acceptor during cellular respiration, allowing for the maximum energy yield in the form of adenosine triphosphate (ATP). This process is critical in municipal wastewater treatment, where aerobic bacteria play a significant role in breaking down organic pollutants, leading to the purification of wastewater.

In contrast, anaerobes do not require oxygen and may even be harmed by its presence, using fermentation or other anaerobic pathways for energy generation. Autotrophs are organisms that produce their own food from inorganic substances, and while some autotrophs may be aerobic, the term itself doesn’t specify the oxygen requirement. Facultative anaerobes are versatile organisms that can switch between aerobic and anaerobic respiration depending on oxygen availability, but they are not exclusively dependent on free dissolved oxygen like aerobes are. Thus, the capacity of aerobes to specifically depend on dissolved oxygen makes this answer the correct choice in the context of the question.