Bacillus azotoformans

The first reaction is catalyzed by a mixed microbial population in which Bacillus azotoformans is the main denitrifying bacteria, and ethanol is the electron donor. Fe(II) is also regenerated from Fe(III) by means of reducing bacteria Dcfcrri-bacteres, using ethanol as the electron donor. These bacteria are found in the Veendam and Eerbeek sludges, as described in a previous section. 

Fujiwara and Fukumori, 1996). Nitric oxide reductase is also known, which lacks heme C and uses quinol as the electron donor (Suharti et al., 2001 de Vries et al., 2003). The cytochrome ebb-type enzyme has a molecular structure similar to the structure of the Cub binding portion in cytochrome c oxidase (Saraste and Castresana, 1994 Van der Oost et al., 1994 Zumft et al., 1994). Moreover, quinol NO reductase from Bacillus azotoformans is known to contain Cua. Nitrous oxide is further reduced to nitrogen gas (N2) by the catalysis of nitrous oxide reductase (N20 reductase) which is a multi-copper protein (Zumft and Matsubara, 1982). The structure of the copper-binding portion in the enzyme has been reported also to be similar to the structure of the Cua binding portion of cytochrome c oxidase (Chamock et al., 2000). 

Suharti, Strampraad MJ, Schroder I, de Vries S (2001) A novel copper A containing menaquinol NO reductase from Bacillus azotoformans. Biochemistry 40 2632-2639 Sumino T, Isaka K, Ikuta H, Saiki Y, Yokota T (2006) Nitrogen removal from waste-water using simultaneous nitrate reduction and anaerobic ammonium oxidation in single reactor. J Biosci Bioeng 102 346-351... 

In addition to cytochrome c oxidase, a protein complex having a very similar fold and arrangement of metal centers is that of the heme-containing nitric oxide reductase (NOR). This protein complex is found in a number of anaerobic bacteria and archaea, including Para coccus cfe/ /7/i5cans, Bacillus azotoformans and Pyrobaculum sero/ Mu/w, and carries out the enzy matic reaction 2NO + 2e + 2H+ = N2O + H2O. (Although this is only a 2-electron reduction, NORs can also reduce O2 to 2H2O, a 4-electron reduction, and at least several CcOs can reduce 2NO to N2O + H2O, a... 

The dimeric NOR from Bacillus azotoformans contains a Cua center located in the smaller subunit, in place of the c-type heme of prototype NOR. Menahydroquinone, but not cytochrome c, functions as electron donor. ... 

Very likely CO2, CO, and N2 were among the main components by the time of the origin of life within the Earth s early atmosphere. In addition, NO, H2, H2O, and sulfuric gases could also have been present, and probably trace amounts of O2 [23]. Thus, it was not too surprising that several molecular links do exist between the evolution of denitrification enzymes and cytochrome c oxidase, the terminal oxidase of aerobic respiration [24]. Perhaps the most important is the homology between nitric oxide reductase and heme/copper cytochrome oxidases, and the presence of the mixed-valence [Cu " (Scys)2Cu " CuA electron-transfer center in nitrous oxide reductases, the quinol-dependent NO reductase from the gram-positive Bacillus azotoformans, and heme/copper cytochrome oxidases [24-27]. 

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