In nitrate reduction test. We have nitrate salt medium and inoculated with soil

Question

In nitrate reduction test. We have nitrate salt medium and inoculated with soil and incubated for 7 days at room temperature. The tube has durham tube and has gas inside. We added the reagents A and B but there was no colour change and added the zinc powder and still no colour change. I am just wondering thus this mean that the microorganism present in the soil reduce the nitrate then to nitrite to nitrogen gas? or nitrate to nitrite to ammonia? Also, thus this mean that the microorganism produce nitrate reductase or does it produce nitrite reductase?

Explanation / Answer

since you have performed positive test for nitrate reduction test and you got no color change it indicates two possibilities

1. nitrate is not reduced.

2. it reduced into ammonia or molecular nitrogen.

also you performed second test by adding Zn powder and you got no color change.

this means no nitrate is present. so now you have eliminate the possibility1.

so that means that denitrification took place and ammonia or molecular nitrogen formed.

it also indicates that organism produces nitrite reductase also.

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