The bacteria that reduce nitrates in the soil into gaseous nitrogen are referred to as

Step 1: Analyze the question The question asks for the name of the bacteria that convert nitrates in the soil into gaseous nitrogen (N₂). This is part of the nitrogen cycle.

Step 2: Explain the concept The nitrogen cycle has several key processes, each carried out by different microorganisms:

• Nitrogen fixation: N₂ → ammonia/nitrates (Rhizobium, Azotobacter)
• Putrefaction/ammonification: dead proteins → ammonia (putrefying bacteria)
• Nitrification: ammonia → nitrites → nitrates (Nitrosomonas, Nitrobacter)
• Denitrification: nitrates → nitrogen gas (Pseudomonas denitrificans, Thiobacillus denitrificans)

Step 3: Work through the options

• A. Nitrifying bacteria: These do the opposite. They convert ammonia to nitrates, so this is wrong.
• B. Denitrifying bacteria: These remove nitrates and release nitrogen gas into the atmosphere. This matches the question.
• C. Putrefying bacteria: They decompose dead proteins into ammonia, so this is wrong.
• D. Saprophytic bacteria: They feed on dead organic matter in general, but this is not the specific nitrate-to-nitrogen process, so this is wrong.

Step 4: Answer The correct answer is B. denitrifying bacteria.

Exam tip: Think of the prefix "de-", which means "remove" or "reverse". Denitrifying bacteria un-do nitrification, taking nitrates out of the soil and returning nitrogen to the air. Denitrification usually happens in waterlogged soils with little oxygen, which is a common follow-up question.