I collected effluent samples from a biorention column with the hopes of collecting denitrifying bacteria, following the procedure described in “Inhibition of assimilatory nitrate reductase activity in soil by glutamine and ammonium analogs” by Gregory W. McCarty and John M. Bremner.
To my knowledge, there are at least 3 microbial processes in soils which use NO3- as a substrate:
- The assimilatory reduction of NO3- to ammonium (NH4+)
- The dissimilatory reduction of NO3- to NH4+
- and denitrification, the dissimilatory reaction of NO3- to dinitrogen (N2) and nitrous oxide (N2O)
In the article, L-Glutamine is used to inhibit the activity of assimilatory NO3- reductase (ANR). Might L-Glutamine affect other microbial processes related to denitrification?
Dear Willow
Your first two reactions are technically possible but the last one is not entirely dissimilatory.
Denitrification is a respiration process (energy producing catabolic) driven mainly by respiratory reduction since denitrifying bacteria use much of the oxidized-N (i.e. NO3, NO2, NO and N2O) as substitutes for O2. The above reactions can be in the cell (membrane) or outside the cell (periplasmic). The use of NO3 for respiration is aided by respiratory nitrate reductase (in membrane) and periplasmic dissimilatory nitrate reductase respectively.
Should assimilatory reduction of NO3 occurs, it is not for the purpose of denitrification (i.e. respiration) and for the purpose of biosynthesis (anabolic) (hence aided by assimilatory nitrate reductase), which is technically a non-respiratory process. If the denitrifying bacteria are in the energy producing (i.e. respiratory) mode, they are unlikely to perform an assimilatory process which is energy taxing.
However, other bacteria might be interested in the assimilatory process hence can reduce NO3 for biosynthesis purpose. Therefore, eliminating the assimilatory nitrate reduction process by inhibition will ensure accurate assessment of the respiratory process of the denitrifying bacteria.
Once NO3 is reduced by respiratory enzymes to NO2 form, the balance of the denitrification is carried out by the remaining NO2 reductase, NO reductase and N2O reductase enzymes. It is generally accepted that the term denitrification can only be used when there is N2O and/or N2 emissions from the process.
It is well known that denitrification is one of the most complex N processes since a sole denitrifying bacteria may not be completing the entire process hence the process is referred to as modular. The main reason is except for the NO reduction (held in the membrane), other reductions can occur outside the host cell (periplasmic) and such reductions can be performed by other bacteria rather than the host bacteria.
As for your query on whether assimilatory nitrate reductase inhibitors can affect the denitrification process, I have not seen any papers/evidence supporting the above process. I hope other workers can shed any light on it.
Kind regards
Selva
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