Which sequence correctly matches each bacterium to its primary role in the nitrogen cycle: nitrogen fixation, nitrification and denitrification?
Azotobacter - nitrogen fixation, Nitrobacter - nitrification, Pseudomonas - denitrification
Azotobacter is a free-living soil bacterium that converts atmospheric nitrogen gas (N2) into ammonia, which plants can use. So its role is nitrogen fixation.
Nitrification is the conversion of ammonia into nitrites and then nitrates. Nitrosomonas changes ammonia to nitrite, and Nitrobacter oxidises nitrite to nitrate, so Nitrobacter is the nitrifying bacterium.
Denitrification returns nitrogen to the air: nitrates in the soil are reduced to nitrogen gas. Pseudomonas is a well-known denitrifying bacterium.
So the correct matching is Azotobacter with nitrogen fixation, Nitrobacter with nitrification and Pseudomonas with denitrification. Every other sequence gives at least two of these bacteria the wrong role.
Hence, Azotobacter - nitrogen fixation, Nitrobacter - nitrification, Pseudomonas - denitrification.
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