Limits...
Comparison of Nitrogen Oxide Metabolism among Diverse Ammonia-Oxidizing Bacteria.

Kozlowski JA, Kits KD, Stein LY - Front Microbiol (2016)

Bottom Line: Therefore, complete nitrifier denitrification did not occur in the two oligotrophic strains, but did occur in meso- and eutrophic strains, even in Nitrosomonas communis Nm2 that lacks an annotated NIR-encoding gene.Regardless of mechanism, all AOB strains produced measureable N2O under tested conditions.This work further confirms that AOB require NOR activity to enzymatically reduce NO to N2O in the nitrifier denitrification pathway, and also that abiotic reactions play an important role in N2O formation, in oligotrophic AOB lacking NOR activity.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Biological Sciences Building, University of Alberta, Edmonton, AB Canada.

ABSTRACT
Ammonia-oxidizing bacteria (AOB) have well characterized genes that encode and express nitrite reductases (NIR) and nitric oxide reductases (NOR). However, the connection between presence or absence of these and other genes for nitrogen transformations with the physiological production of nitric oxide (NO) and nitrous oxide (N2O) has not been tested across AOB isolated from various trophic states, with diverse phylogeny, and with closed genomes. It is therefore unclear if genomic content for nitrogen oxide metabolism is predictive of net N2O production. Instantaneous microrespirometry experiments were utilized to measure NO and N2O emitted by AOB during active oxidation of ammonia (NH3) or hydroxylamine (NH2OH) and through a period of anoxia. This data was used in concert with genomic content and phylogeny to assess whether taxonomic factors were predictive of nitrogen oxide metabolism. Results showed that two oligotrophic AOB strains lacking annotated NOR-encoding genes released large quantities of NO and produced N2O abiologically at the onset of anoxia following NH3-oxidation. Furthermore, high concentrations of N2O were measured during active O2-dependent NH2OH oxidation by the two oligotrophic AOB in contrast to non-oligotrophic strains that only produced N2O at the onset of anoxia. Therefore, complete nitrifier denitrification did not occur in the two oligotrophic strains, but did occur in meso- and eutrophic strains, even in Nitrosomonas communis Nm2 that lacks an annotated NIR-encoding gene. Regardless of mechanism, all AOB strains produced measureable N2O under tested conditions. This work further confirms that AOB require NOR activity to enzymatically reduce NO to N2O in the nitrifier denitrification pathway, and also that abiotic reactions play an important role in N2O formation, in oligotrophic AOB lacking NOR activity.

No MeSH data available.


Related in: MedlinePlus

Instantaneous measurement of O2 consumption and NO or N2O during oxidation of 2 mM NH4Cl.Nitrosomonas europaea(A,B), N. communis(C,D), Nitrosomonas sp. Is79A3 (E,F), N. ureae(G,H), Nitrosospira multiformis(I,J). Panels are single representative measurements of reproducible results (n = 3). Note differences in scale of x-axis for traces of NO production during NH3-oxidation.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4940428&req=5

Figure 2: Instantaneous measurement of O2 consumption and NO or N2O during oxidation of 2 mM NH4Cl.Nitrosomonas europaea(A,B), N. communis(C,D), Nitrosomonas sp. Is79A3 (E,F), N. ureae(G,H), Nitrosospira multiformis(I,J). Panels are single representative measurements of reproducible results (n = 3). Note differences in scale of x-axis for traces of NO production during NH3-oxidation.

Mentions: Measurement of NO or N2O production during oxidation of NH3 or NH2OH were compared among the 5 strains and revealed that all AOB produce measureable quantities of NO during active oxidation of NH3 (Figures 2A,C,E,G,I). Although each AOB had a unique and dynamic NO production profile, making comparative rate calculations impractical, all strains produced>50 nM NO (per 1 × 1010 total cells) prior to anoxia in the MR chamber. N. europaea produced the least amount of NO compared to the other strains during active oxidation and prior to anoxia (Figure 2A; Supplementary Table S1). As reported previously (Kozlowski et al., 2016c) N. multiformis began re-consuming NO once ca. 50% O2 was left in the MR-chamber (Figure 2I) and both N. europaea and N. communis re-consumed a small amount of NO following anoxia in the MR-chamber (Figures 2A,C). Interestingly, either immediately upon O2 depletion in the case of Nitrosomonas sp. Is79A3 (Figure 2E) or ca. 5 min. post-anoxia for N. ureae, these two strains released massive quantities of NO outside the limit for measurement by the ami-600 NO microsensor (Figures 2E,G). Unlike the other AOB strains, neither Nitrosomonas sp. Is79A3 nor N. ureae re-consumed NO during active NH3-oxidation or following anoxia in the MR-chamber.


Comparison of Nitrogen Oxide Metabolism among Diverse Ammonia-Oxidizing Bacteria.

Kozlowski JA, Kits KD, Stein LY - Front Microbiol (2016)

Instantaneous measurement of O2 consumption and NO or N2O during oxidation of 2 mM NH4Cl.Nitrosomonas europaea(A,B), N. communis(C,D), Nitrosomonas sp. Is79A3 (E,F), N. ureae(G,H), Nitrosospira multiformis(I,J). Panels are single representative measurements of reproducible results (n = 3). Note differences in scale of x-axis for traces of NO production during NH3-oxidation.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4940428&req=5

Figure 2: Instantaneous measurement of O2 consumption and NO or N2O during oxidation of 2 mM NH4Cl.Nitrosomonas europaea(A,B), N. communis(C,D), Nitrosomonas sp. Is79A3 (E,F), N. ureae(G,H), Nitrosospira multiformis(I,J). Panels are single representative measurements of reproducible results (n = 3). Note differences in scale of x-axis for traces of NO production during NH3-oxidation.
Mentions: Measurement of NO or N2O production during oxidation of NH3 or NH2OH were compared among the 5 strains and revealed that all AOB produce measureable quantities of NO during active oxidation of NH3 (Figures 2A,C,E,G,I). Although each AOB had a unique and dynamic NO production profile, making comparative rate calculations impractical, all strains produced>50 nM NO (per 1 × 1010 total cells) prior to anoxia in the MR chamber. N. europaea produced the least amount of NO compared to the other strains during active oxidation and prior to anoxia (Figure 2A; Supplementary Table S1). As reported previously (Kozlowski et al., 2016c) N. multiformis began re-consuming NO once ca. 50% O2 was left in the MR-chamber (Figure 2I) and both N. europaea and N. communis re-consumed a small amount of NO following anoxia in the MR-chamber (Figures 2A,C). Interestingly, either immediately upon O2 depletion in the case of Nitrosomonas sp. Is79A3 (Figure 2E) or ca. 5 min. post-anoxia for N. ureae, these two strains released massive quantities of NO outside the limit for measurement by the ami-600 NO microsensor (Figures 2E,G). Unlike the other AOB strains, neither Nitrosomonas sp. Is79A3 nor N. ureae re-consumed NO during active NH3-oxidation or following anoxia in the MR-chamber.

Bottom Line: Therefore, complete nitrifier denitrification did not occur in the two oligotrophic strains, but did occur in meso- and eutrophic strains, even in Nitrosomonas communis Nm2 that lacks an annotated NIR-encoding gene.Regardless of mechanism, all AOB strains produced measureable N2O under tested conditions.This work further confirms that AOB require NOR activity to enzymatically reduce NO to N2O in the nitrifier denitrification pathway, and also that abiotic reactions play an important role in N2O formation, in oligotrophic AOB lacking NOR activity.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Biological Sciences Building, University of Alberta, Edmonton, AB Canada.

ABSTRACT
Ammonia-oxidizing bacteria (AOB) have well characterized genes that encode and express nitrite reductases (NIR) and nitric oxide reductases (NOR). However, the connection between presence or absence of these and other genes for nitrogen transformations with the physiological production of nitric oxide (NO) and nitrous oxide (N2O) has not been tested across AOB isolated from various trophic states, with diverse phylogeny, and with closed genomes. It is therefore unclear if genomic content for nitrogen oxide metabolism is predictive of net N2O production. Instantaneous microrespirometry experiments were utilized to measure NO and N2O emitted by AOB during active oxidation of ammonia (NH3) or hydroxylamine (NH2OH) and through a period of anoxia. This data was used in concert with genomic content and phylogeny to assess whether taxonomic factors were predictive of nitrogen oxide metabolism. Results showed that two oligotrophic AOB strains lacking annotated NOR-encoding genes released large quantities of NO and produced N2O abiologically at the onset of anoxia following NH3-oxidation. Furthermore, high concentrations of N2O were measured during active O2-dependent NH2OH oxidation by the two oligotrophic AOB in contrast to non-oligotrophic strains that only produced N2O at the onset of anoxia. Therefore, complete nitrifier denitrification did not occur in the two oligotrophic strains, but did occur in meso- and eutrophic strains, even in Nitrosomonas communis Nm2 that lacks an annotated NIR-encoding gene. Regardless of mechanism, all AOB strains produced measureable N2O under tested conditions. This work further confirms that AOB require NOR activity to enzymatically reduce NO to N2O in the nitrifier denitrification pathway, and also that abiotic reactions play an important role in N2O formation, in oligotrophic AOB lacking NOR activity.

No MeSH data available.


Related in: MedlinePlus