The biochemistry of the nitrifying organisms. 5. Nitrite oxidation by Nitrobacter

Abstract

Nitrobacter is an autotrophic soil bacterium that derives its entire energy supply from the reaction NO2-+ O2 = NO3-+17 kcal. Apart from the early studies of Meyerhof (1916 a, b), there has been little biochemical work done on this organism since its discovery and isolation by Winogradsky (1890, 1891). The present paper records investigations into the mechanism of niitrite oxidation by Nitrobacter. Preliminary notes on some of our results have already appeared (Lees & Simpson, 1955a, b). MATERIALS AND METHODS Growth of the organisms. Nitrobacter was obtained from an Aberdeen garden soil by serial subculture in a medium made up as follows. To 10 1. of water were added 30 g. of KH2P04, 1 g. of CaSO4, 0 5 g. of MgCl2, 0 01 g. of MnCl2, 0-2 ml. of dialysed iron (B.P.). By addition of lOM-NaOH, the pH was adjusted to 7-8, which is the optimum pH for the strain of Nitrobacter used (Lees, 1954). The solution was filtered and, after addition of the appropriate amount of NaN02, sterilized at 1200 for 20 min. This medium (medium G) was used also for the propagation of the stock cultures which provided inocula for large-scale batch cultures. For largescale batch cultures 100 ml. of the carbonate-phosphate suspension, used by Lees (1952) for the culture of Nitrosomonas, was added to each 101. of medium G before sterilization. Batch cultures were used for preparing suspensions of Nitrobacter cells suitable for biochemical study; the carbonate-phosphate suspension was added to facilitate the separation of these cells after growth. Nitrobacter, unulike Nitrosomonas, does not require a solid surface for growth, but Nitrobacter cells did adhere in some measure to the solid particles in the suspension and, in any case, were entrained by them when the cells were separated from the bulk of the medium by centrifuging.

Unexpected Diversity of Chlorite Dismutases: a Catalytically Efficient Dimeric Enzyme from Nitrobacter winogradskyi

“…Chlorate is transformed to chlorite by Nar due to the structural similarity between chlorate and nitrate (see Logan et al [30] and references cited therein). Consistent with the similarity of Nxr to Nar, Nitrobacter winogradskyi and an environmental Nitrobacter isolate indeed are able to reduce chlorate and even can oxidize nitrite using chlorate instead of O 2 as an electron acceptor during anoxic incubations (18,29). An active NwCld should offer Nitrobacter protection from the chlorite produced under these conditions, but in a previous study, chlorate-driven nitrite oxidation by Nitrobacter diminished after a few hours, most likely due to inhibition by chlorite (29).…”

“…Consistent with the similarity of Nxr to Nar, Nitrobacter winogradskyi and an environmental Nitrobacter isolate indeed are able to reduce chlorate and even can oxidize nitrite using chlorate instead of O 2 as an electron acceptor during anoxic incubations (18,29). An active NwCld should offer Nitrobacter protection from the chlorite produced under these conditions, but in a previous study, chlorate-driven nitrite oxidation by Nitrobacter diminished after a few hours, most likely due to inhibition by chlorite (29). However, this inhibition was observed after incubation of Nitrobacter in nitrite media containing relatively high chlorate concentrations (4.2 to 17 mM [29] or 10 mM [18]), which presumably led to the production of large amounts of chlorite.…”

“…An active NwCld should offer Nitrobacter protection from the chlorite produced under these conditions, but in a previous study, chlorate-driven nitrite oxidation by Nitrobacter diminished after a few hours, most likely due to inhibition by chlorite (29). However, this inhibition was observed after incubation of Nitrobacter in nitrite media containing relatively high chlorate concentrations (4.2 to 17 mM [29] or 10 mM [18]), which presumably led to the production of large amounts of chlorite. The same studies found that Nitrobacter was strongly inhibited by externally added chlorite above 1 mM, but inhibition was only weak with 0.3 mM (29) or less than 0.1 mM (18).…”

“…However, this inhibition was observed after incubation of Nitrobacter in nitrite media containing relatively high chlorate concentrations (4.2 to 17 mM [29] or 10 mM [18]), which presumably led to the production of large amounts of chlorite. The same studies found that Nitrobacter was strongly inhibited by externally added chlorite above 1 mM, but inhibition was only weak with 0.3 mM (29) or less than 0.1 mM (18). In this context, it is noteworthy that toxic effects of chlorite on other bacteria have been observed at much lower concentrations of 0.01 to 0.02 mM (47).…”

Biological ammonia removal from drinking water in fluidized bed reactors

“…Yields reported [5] for Nitrobacter based on experimental mixed culture are between 0.02 and 0.07 and that based on pure culture is 0.084. Other values for Nitrobacter yields were reported [10,11] as 0.02 for batch culture and for continuous culture [3] between a 0.04 and 0.07. Beccari et al [12] obtained a yield value of 0.07 for Nitrobacter.…”