In a stream with zero DO, what is the expected predominant microbial activity?

In a stream with zero DO, what is the expected predominant microbial activity?

• A. Aerobic bacteria
• B. Anaerobic bacteria
• C. Fungi
• D. Algae

Answer: (B)

When dissolved oxygen is absent, microbes can’t rely on aerobic respiration. In anoxic conditions, anaerobic bacteria take over, using alternative electron acceptors (like nitrate or sulfate) or fermenting organic matter to release energy. This shift to anaerobic metabolism is why anaerobic bacteria are the predominant activity in a stream with zero DO. Fungi and algae typically need oxygen (and algae also need light), so they don’t dominate when oxygen isn’t available.

When dissolved oxygen is absent, microbes can’t rely on aerobic respiration. In anoxic conditions, anaerobic bacteria take over, using alternative electron acceptors (like nitrate or sulfate) or fermenting organic matter to release energy. This shift to anaerobic metabolism is why anaerobic bacteria are the predominant activity in a stream with zero DO. Fungi and algae typically need oxygen (and algae also need light), so they don’t dominate when oxygen isn’t available.