Denitrifying bacteria are a class of what type of bacteria?

• A. Aerobic
• B. Facultative
• C. Anaerobic
• D. Microaerophilic

Answer: (B)

Denitrifying bacteria can switch their respiration based on oxygen availability. They typically use oxygen when it’s present, but when oxygen becomes scarce, they switch to nitrate as the terminal electron acceptor and reduce nitrate through to nitrogen gas or nitrous oxide. That adaptability to grow with or without oxygen is the hallmark of facultative organisms, which is why this classification fits denitrifiers best. They’re not restricted to oxygen (a characteristic of strictly aerobic bacteria) or limited to no oxygen at all (which would describe obligate anaerobes), nor do they require only tiny amounts of oxygen (microaerophilic). This flexible respiratory capability is what makes them fit as facultative.