MCB2010L lab 28 Nitrate Reduction test

Principal of test

Purpose is to test organism's ability to reduce nitrate (NO3) to nitrite (NO2) or further to nitrogen gas (N2) or ammonia (NH3) using anaerobic respiration

Durham tube

Small inverted tube placed inside test tube to trap gas

Regents used for the test

• Nitrate A (sulfanilic acid)

Nitrate B (a-naphthylamine )

Zinc powder is used after no initial reaction to confirm presence of nitrate.

Zinc powder

Adored when there is no color change after adding reagent A and B.

• if red forms after zinc nitrate is still present → negative result (organism did not reduce nitrate)

• If no color change after zinc nitrate was reduced to nitrogen gas or ammonia → positive result

Color Changes/ positive reactions, negative reactions

Red color after reagent A and B: positive for nitrite (nitrate to nitrite)

No color change after A and B but red after zinc: negative (nitrate is still present)

No color change after everything: positive (complete reduction to nitrogen gas or ammonia)

Organisms positive for nitrite

E.coli

Organisms positive for ammonia

P.augernosa (18)

Presence of nitrogen

Indicated by gas in the Durham tube and no color change after zinc → confirms full reduction to nitrogen gas (N2) a positive result