Nitrifying Bacteria

Abstract

The term denitrification originally was coined to describe the loss of nitrate to gaseous products in decomposing organic matter. Such elementary observations were made by H. Davy (USA), J. Reiset and T. Schloesing (France), and F. von Goppelsroder (Switzerland) and date back well over a century, but a landmark in the development ofthe field was the comprehensive study by Gayon and Dupetit (1886) using two pure cultures of what was then called "Bacterium denitrificans" strains a and (3. In these early studies ofdenitrification, the intermediate gaseous species, nitric oxide (NO) and nitrous oxide (N,O) were both already observed. The role of nitrates, however, was initially believed to be limited to supply oxygen for combustion, as graphically expressed by Giltay and Aberson (1892): "Cette decomposition fait songer, dans une certaine mesure, Ii l'explosion de la poudre Ii canon." Observations of chemolithotrophic growth with nitrate and developments of new concepts of energy metabolism (Kluyver and Donker, 1926) led to the currently accepted view of anaerobic respiration. The history of denitrification research has been vividly traced by Payne (1981). Denitrification is a bacterial respiratory process that couples electron transport phosphorylation to the stepwise, sequential reduction of nitrogenous oxides. The phenomena that characterize this process sensu stricto are I) cell growth with nitrate or nitrite as oxidants for electron transport and 2) concomitant evolution ofa gas species, either NO, N,O, or N,. Usually, organic compounds are oxidized during denitrification but in a few cases oxidation of inorganic compounds occurs, such as reduced sulfur compounds by sulfur-oxidizing bacteria (genera Thermothrix, Thiobacillus, Thiomicrospira, and Thiosphaera), of hydrogen by hydrogen bacteria (genera Alcaligenes, Bradyrhizobium, Paracoccus, Pseudomonas, and Rhizobium), or even of ammonia or nitrite by nitrifYing bacteria (genera Nitrosomonas and Nitrobacter, respectively (cont in the article)