Nitrate reduction and denitrification process

Nitrate ions can be transformed by a variety of organisms or organic matter through the process of assimilatory nitrate reduction. A heterogeneous group of micro-organisms consist of many bacterial, fungal and algal species are capable of assimilatory nitrate reduction. The process of assimilatory nitrate reduction involves several enzyme systems consisting of nitrate and nitrite reductases to form ammonia which can be incorporated into amino acids. The enzyme system appears to involve soluble metalloproteinase and require reduced co factors. Assimilating nitrate enzyme systems in bacteria, algae and fungi, which have been examined, are represented or suppressed by the presence of ammonia or reduced nitrogenous organic metabolites in the growth environment. Normal atmospheric concentrations of oxygen do not appear to inhibit the assimilatory nitrate reductase enzymes systems. Assimilatory nitrate reduction does not result in the accumulation or compounding of high concentration of extracellular ammonium ions; ammonia is incorporated relatively rapidly into organic nitrogen, excess ammonium acts through feedback inhibition to shut off nitrate reduction.

In the absence or lack of oxygen, nitrate can stand as terminal electron acceptors; this process is known as nitrate or anaerobic respiration. Nitrate ions can as well be converted to molecular nitrogen through denitrification. Some micro-organisms such as Psendomonas denitrificans produce nitrogen gases. Utilization of glucose through nitrate reduction can be expressed as C₆H₁₂O₆+4NO₃ – 6CO₂+6H₂O+2N₂.

When nitrate ions serve as terminal electron acceptor, the oxidation state of the nitrogen is then reduced, leading to dissimulatory of nitrogen reduction. Dissimilatory nitrate reduction through nitrate can result in the formation of ammonia or in the production of gaseous form of nitrogen. The initial enzymes involved in these prosesses and dissimilatory nitrate and nitrite reductases are particle bound, competively inhibited by oxygen and not inhibited by ammonia in contrast to assimilatory nitrate reductases which are soluble, inhibited by ammonia and not substantially inhibited by oxygen. Denitrifications generally take place under anaerobic conditions or under conditions of reduced oxygen tension.