Question

Why is oxygen toxic to anaerobic bacteria?

Answer 1

Hint: An anaerobic organism is an organism that can live in the absence of oxygen in its environment. They do not require oxygen for their growth and in their metabolic reactions. There are two types of anaerobic bacteria- obligate anaerobic (These are the bacteria that don’t use oxygen) and facultative anaerobic bacteria (These are the bacteria which can use oxygen for respiration when oxygen is present and in the absence of oxygen they do anaerobic reaction).

Complete answer:
Obligate anaerobes, which can live only in the absence of oxygen, do not possess the defenses that make aerobic life possible and therefore cannot survive in the air or in presence of oxygen.
Obligate anaerobes are microbes which are killed by normal atmospheric concentrations of oxygen. Oxygen tolerance differs between anaerobic bacterial species. Some of the bacteria are capable of surviving in up to 8% oxygen whereas other species can lose viability when the oxygen concentration is less than 0.5%. Anaerobic microorganisms lack and don’t possess certain enzymes such as catalase, oxidase, superoxide dismutase that are essential for bacteria to survive in the presence of oxygen. Due to the absence of these enzymes oxygen becomes toxic to anaerobic bacteria.
Aerobes can survive in the presence of oxygen only by virtue of an intricate or detailed system of defenses. Without these defenses, enzyme systems in the organisms weaken to function and the organisms ultimately die.

Note:
Anaerobic bacteria are found in oxygen-depleted areas like in our digestive system. They produce less amount of energy as compared with aerobic bacteria. Nitrate, methane, sulfide, and acetate-like products are produced by them. They require energy input to proceed with the reaction.