California Wastewater Treatment Operator Practice Exam

What type of microorganism can use nitrate as a source of oxygen?

1. anaerobic bacteria

2. facultative bacteria

3. aerobic bacteria

4. archaea

The correct answer is: facultative bacteria

The correct type of microorganism that can use nitrate as a source of oxygen is facultative bacteria. These organisms are capable of switching between aerobic respiration, using oxygen, and anaerobic respiration, which can involve the reduction of nitrate. In environments where oxygen is scarce, facultative bacteria utilize nitrate to carry out their metabolic processes, thus allowing them to thrive in varying conditions. Facultative bacteria are highly adaptable, enabling them to utilize available electron acceptors, such as nitrate, when oxygen is not present. This characteristic is essential in wastewater treatment, where dynamic conditions often fluctuate between aerobic and anaerobic environments. Anaerobic bacteria, while they do not require oxygen, do not specifically use nitrate as a source of oxygen; instead, they rely on other substrates for their metabolism. Aerobic bacteria primarily depend on oxygen for their respiration and would not utilize nitrate for that purpose. Archaea, on the other hand, include a diverse range of microorganisms, some of which can reduce nitrate, but they are not specifically categorized in the same functional way as facultative bacteria regarding the direct use of nitrate as an oxygen source. Thus, facultative bacteria stand out for their unique ability to adapt their metabolic processes depending on the availability of oxygen or nitrate.