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>>Someone else on the APD asked about ammonia appearing after the
>>addition of several Jobe's sticks to the substrate. In the anaerobic
>>environment in the substrate, bacteria act upon nitrate and reduce
>>it to ammonia.
>This is the second time I've seen reference to this. It is my
>understanding that nitrate does NOT get reduced to ammonia, but to
>elemental N2. I thought there was something about the bacteria using
>the oxygen for energy and being lazy about not spending the time to
>scrounge up enough H to build ammonia.
While we are all familiar with the process of nitrification
(NH4-->NO2-->NO3), the reverse process, dissimilation (aka nitrate
respiration) can also occur in our aquariums.
Dissimilation is an anaerobic process, and bacteria that can do this
can either be true anaerobes, or aerobes that can switch to anaerobic
respiration under anoxic conditions. Pseudomonas is a common aerobic
bacteria that can switch.
During dissimilation, bacteria use nitrate in place of oxygen as an
electron acceptor. Nitrate becomes reduced to other forms with lower
oxidation numbers, including nitrite, ammonia, nitrous oxide (N2O), or
nitrogen (N2). Different bacteria produce different end products.
When nitrate becomes completely reduced to N2O or N2, dissimilation is
known as denitrification.
A good reference on this topic is "Bacterial Metabolism", by Gerhard