Which bacteria convert nitrates into nitrogen gas, often in damp soils?

• A. Nitrification
• B. Denitrifying Bacteria
• C. Nitrogen Fixing Bacteria
• D. Mutations

Answer: (B)

Denitrification is the process by which certain bacteria use nitrate as a terminal electron acceptor in respiration when oxygen is scarce, such as in damp or waterlogged soils. In these low-oxygen conditions, nitrate is reduced stepwise to nitrite, then to nitrous oxide, and finally to nitrogen gas, which bubbles up into the atmosphere. This removes fixed nitrogen from the soil system and explains why nitrates can disappear from damp soils.

Nitrification, by contrast, requires oxygen and oxidizes ammonium to nitrate, not producing gaseous nitrogen. Nitrogen-fixing bacteria take atmospheric N2 and convert it to ammonia for biosynthesis. Mutations are unrelated to these nitrogen-transforming processes.