Potential of Aerobic Denitrification by Pseudomonas stutzeri TR2 To Reduce Nitrous Oxide Emissions from Wastewater Treatment Plants

Abstract

In contrast to most denitrifiers studied so far, Pseudomonas stutzeri TR2 produces low levels of nitrous oxide (N 2 O) even under aerobic conditions. We compared the denitrification activity of strain TR2 with those of various denitrifiers in an artificial medium that was derived from piggery wastewater. Strain TR2 exhibited strong denitrification activity and produced little N 2 O under all conditions tested. Its growth rate under denitrifying conditions was near comparable to that under aerobic conditions, showing a sharp contrast to the lower growth rates of other denitrifiers under denitrifying conditions. Strain TR2 was tolerant to toxic nitrite, even utilizing it as a good denitrification substrate. When both nitrite and N 2 O were present, strain TR2 reduced N 2 O in preference to nitrite as the denitrification substrate. This bacterial strain was readily able to adapt to denitrifying conditions by expressing the denitrification genes for cytochrome cd 1 nitrite reductase (NiR) (nirS) and nitrous oxide reductase (NoS) (nosZ). Interestingly, nosZ was constitutively expressed even under nondenitrifying, aerobic conditions, consistent with our finding that strain TR2 preferred N 2 O to nitrite. These properties of strain TR2 concerning denitrification are in sharp contrast to those of well-characterized denitrifiers. These results demonstrate that some bacterial species, such as strain TR2, have adopted a strategy for survival by preferring denitrification to oxygen respiration. The bacterium was also shown to contain the potential to reduce N 2 O emissions when applied to sewage disposal fields.Wastewater treatment processes produce one of the major greenhouse effect gases, nitrous oxide (N 2 O) (7,25,30). The global warming potential of N 2 O relative to that of carbon dioxide (CO 2 ) is 298 for a 100-year time horizon, and its concentration in the atmosphere continues to increase by about 0.26% per year (9). Nitrogen removal in wastewater treatment plants is essentially based on the activities of nitrifying and denitrifying microorganisms, both of which are inhabitants of activated sludge. Nitrifying bacteria aerobically oxidize ammonium to nitrite (NO 2 Ϫ ) and nitrate (NO 3 Ϫ ), which are then reduced anaerobically by denitrifying bacteria to gaseous nitrogen forms, such as N 2 O and dinitrogen (N 2 ). It has long been known that N 2 O can be produced during both nitrification and denitrification processes of wastewater treatment (3, 19, 23), but the cause of N 2 O emission during the nitrification process was not clear. We recently showed, however, using activated sludge grown under conditions that mimicked a piggery wastewater disposal, that N 2 O emission during the nitrification process depends on denitrification by ammonia-oxidizing bacteria (Nitrosomonas) (18). On the other hand, it is believed that denitrifying bacteria produce N 2 O as a byproduct when anaerobiosis is insufficient during the denitrification process, because N 2 O reductase is the enzyme that is most sensitive to oxygen (6). Pigg...

Anaerobic Metabolism in Haloferax Genus

“…Pseudomonas stutzeri (Miyahara et al, 2010). These strains can oxidize ammonium to nitrite and, simultaneously, can reduce nitrates and nitrites to N 2 by aerobic denitrification (Guo et al, 2013).…”

Identification and isolation of active N2O reducers in rice paddy soil

“…For FSC isolation, cell-division inhibitors (20 mg nalidixic acid, 10 mg pipemidic acid, 10 mg piromidic and 10 mg cephalexin) (Joux and Lebaron, 1997) were added to the vial together with N 2 O and succinate. The vial was then incubated under an Ar:N 2 O (95:5) atmosphere and static conditions at 30 1C for 24 h. CO 2 and N 2 O gases in the headspace of the vial were quantified by gas chromatography (GC) as described previously (Saito et al, 2008 were separately quantified by GC-mass spectrometry (GC/MS) using the gas chromatograph/mass spectrometer QP5050 (Shimadzu, Kyoto, Japan) as described elsewhere (Miyahara et al, 2010). Succinate was extracted from soil with 5 ml water and quantified by high-performance liquid chromatography as described previously (Saito et al, 2008).…”

Survival of the Aerobic DenitrifierPseudomonas stutzeriStrain TR2 during Co-Culture with Activated Sludge under Denitrifying Conditions

“…17) Luria-Bertani (LB) medium was used for seed culture and preculture. Mixed liquor medium (MLM), derived from piggery wastewater, 18) was used to passage cultures to mimic a wastewater treatment field. MLM was prepared by mixing membrane sequencing batch bioreactor (MSBR)-treated water (pH 8.3) and digestion liquid after methane fermentation of piggery wastewater (DLMF) (pH 8.3) at a ratio of 59:1, followed by supplementation with a trace element solution.…”

“…We further found that the low N 2 O emission of strain TR2 is dependent on its preference for N 2 O as electron acceptor together with constitutive expression of the nosZ (N 2 O reductase) gene even under nondenitrifying, aerobic conditions. 18) Hence we suggested that strain TR2 should be useful for reducing N 2 O emissions when used to augment wastewater treatment processes that tend to emit large amounts of N 2 O. 18) Nevertheless, there has been little work on applying such a bacterial strain to wastewater treatment fields to reduce N 2 O emissions (bioaugmentation).…”

“…18) Hence we suggested that strain TR2 should be useful for reducing N 2 O emissions when used to augment wastewater treatment processes that tend to emit large amounts of N 2 O. 18) Nevertheless, there has been little work on applying such a bacterial strain to wastewater treatment fields to reduce N 2 O emissions (bioaugmentation). To the best of our knowledge, only nitrite oxidizing bacteria have successfully been applied to a composting process to reduce N 2 O emissions.…”