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Diverse electron sources support denitrification under hypoxia in the obligate methanotroph Methylomicrobium album strain BG8.

Kits KD, Campbell DJ, Rosana AR, Stein LY - Front Microbiol (2015)

Bottom Line: Aerobic methane-oxidizing bacteria (MOB) are a diverse group of microorganisms that are ubiquitous in natural environments.Along with anaerobic MOB and archaea, aerobic methanotrophs are critical for attenuating emission of methane to the atmosphere.Our results suggest that expression of denitrification genes, found widely within genomes of aerobic methanotrophs, allow the coupling of substrate oxidation to the reduction of nitrogen oxide terminal electron acceptors under oxygen limitation.

View Article: PubMed Central - PubMed

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

ABSTRACT
Aerobic methane-oxidizing bacteria (MOB) are a diverse group of microorganisms that are ubiquitous in natural environments. Along with anaerobic MOB and archaea, aerobic methanotrophs are critical for attenuating emission of methane to the atmosphere. Clearly, nitrogen availability in the form of ammonium and nitrite have strong effects on methanotrophic activity and their natural community structures. Previous findings show that nitrite amendment inhibits the activity of some cultivated methanotrophs; however, the physiological pathways that allow some strains to transform nitrite, expression of gene inventories, as well as the electron sources that support this activity remain largely uncharacterized. Here we show that Methylomicrobium album strain BG8 utilizes methane, methanol, formaldehyde, formate, ethane, ethanol, and ammonia to support denitrification activity under hypoxia only in the presence of nitrite. We also demonstrate that transcript abundance of putative denitrification genes, nirS and one of two norB genes, increased in response to nitrite. Furthermore, we found that transcript abundance of pxmA, encoding the alpha subunit of a putative copper-containing monooxygenase, increased in response to both nitrite and hypoxia. Our results suggest that expression of denitrification genes, found widely within genomes of aerobic methanotrophs, allow the coupling of substrate oxidation to the reduction of nitrogen oxide terminal electron acceptors under oxygen limitation. The present study expands current knowledge of the metabolic flexibility of methanotrophs by revealing that a diverse array of electron donors support nitrite reduction to nitrous oxide under hypoxia.

No MeSH data available.


Related in: MedlinePlus

Growth, CH4 and O2 consumption, and N2O production by Methylomicrobium album strain BG8 cultivated on NMS and NMS plus 1 mM NaNO2. Methylomicrobium album strain BG8 was cultivated for 5 days in 100 mL of NMS (black triangles) or NMS + 1 mM NO2- (gray dashed squares) media in 300 mL closed glass Wheaton bottles sealed with butyl rubber septum caps. The initial headspace gas-mixing ratio of CH4 to O2 was 1.6:1. Cell density (A) was measured using direct count with a Petroff–Hausser counting chamber and headspace gas concentrations of O2(B), CH4(C) and N2O (D) were measured using GC-TCD. All data points represent the mean ± SD for six biological replicates (n = 6).
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Figure 1: Growth, CH4 and O2 consumption, and N2O production by Methylomicrobium album strain BG8 cultivated on NMS and NMS plus 1 mM NaNO2. Methylomicrobium album strain BG8 was cultivated for 5 days in 100 mL of NMS (black triangles) or NMS + 1 mM NO2- (gray dashed squares) media in 300 mL closed glass Wheaton bottles sealed with butyl rubber septum caps. The initial headspace gas-mixing ratio of CH4 to O2 was 1.6:1. Cell density (A) was measured using direct count with a Petroff–Hausser counting chamber and headspace gas concentrations of O2(B), CH4(C) and N2O (D) were measured using GC-TCD. All data points represent the mean ± SD for six biological replicates (n = 6).

Mentions: Methylomicrobium album strain BG8 was cultivated in NMS or NMS supplemented with NO2- over 120 h to determine the effect of NO2- on growth, O2 and CH4 consumption, and N2O production (Figure 1). The total amount of nitrogen was kept constant to eliminate a difference in N-availability and salt concentration between treatments. All of the cultures were initiated at an oxygen (O2) tension of 19.5 ± 0.7% (Figure 1B). As observed previously (Nyerges et al., 2010), NO2- amendment (1 mM) did not have an inhibitory effect on growth or substrate consumption of M. album strain BG8 (Figures 1A–C and Supplementary Table S1). The limiting substrate in all treatments was O2, as demonstrated by supplementing cultures with additional O2 (20 mL) after 48 h of growth and observing a significant increase in optical density in comparison to cultures not receiving additional O2 (Supplementary Figure S1). N2O production occurred only in the NMS plus NO2- cultures (Figure 1D). N2O production was first apparent in the headspace of NO2- amended cultures at 72 h of growth when O2 reached ca. 1.8% of the headspace and continued up to the termination of the experiment (120 h) at a rate of 9.3 × 10-18 mol N2O per cell per hour (Figure 1D). After 120 h of growth, the N2O yield percentage from the added NO2- (100 μmol) was 5.1 ± 0.2% (5.1 ± 0.2 μmol) in the NMS + NO2- cultures.


Diverse electron sources support denitrification under hypoxia in the obligate methanotroph Methylomicrobium album strain BG8.

Kits KD, Campbell DJ, Rosana AR, Stein LY - Front Microbiol (2015)

Growth, CH4 and O2 consumption, and N2O production by Methylomicrobium album strain BG8 cultivated on NMS and NMS plus 1 mM NaNO2. Methylomicrobium album strain BG8 was cultivated for 5 days in 100 mL of NMS (black triangles) or NMS + 1 mM NO2- (gray dashed squares) media in 300 mL closed glass Wheaton bottles sealed with butyl rubber septum caps. The initial headspace gas-mixing ratio of CH4 to O2 was 1.6:1. Cell density (A) was measured using direct count with a Petroff–Hausser counting chamber and headspace gas concentrations of O2(B), CH4(C) and N2O (D) were measured using GC-TCD. All data points represent the mean ± SD for six biological replicates (n = 6).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4594100&req=5

Figure 1: Growth, CH4 and O2 consumption, and N2O production by Methylomicrobium album strain BG8 cultivated on NMS and NMS plus 1 mM NaNO2. Methylomicrobium album strain BG8 was cultivated for 5 days in 100 mL of NMS (black triangles) or NMS + 1 mM NO2- (gray dashed squares) media in 300 mL closed glass Wheaton bottles sealed with butyl rubber septum caps. The initial headspace gas-mixing ratio of CH4 to O2 was 1.6:1. Cell density (A) was measured using direct count with a Petroff–Hausser counting chamber and headspace gas concentrations of O2(B), CH4(C) and N2O (D) were measured using GC-TCD. All data points represent the mean ± SD for six biological replicates (n = 6).
Mentions: Methylomicrobium album strain BG8 was cultivated in NMS or NMS supplemented with NO2- over 120 h to determine the effect of NO2- on growth, O2 and CH4 consumption, and N2O production (Figure 1). The total amount of nitrogen was kept constant to eliminate a difference in N-availability and salt concentration between treatments. All of the cultures were initiated at an oxygen (O2) tension of 19.5 ± 0.7% (Figure 1B). As observed previously (Nyerges et al., 2010), NO2- amendment (1 mM) did not have an inhibitory effect on growth or substrate consumption of M. album strain BG8 (Figures 1A–C and Supplementary Table S1). The limiting substrate in all treatments was O2, as demonstrated by supplementing cultures with additional O2 (20 mL) after 48 h of growth and observing a significant increase in optical density in comparison to cultures not receiving additional O2 (Supplementary Figure S1). N2O production occurred only in the NMS plus NO2- cultures (Figure 1D). N2O production was first apparent in the headspace of NO2- amended cultures at 72 h of growth when O2 reached ca. 1.8% of the headspace and continued up to the termination of the experiment (120 h) at a rate of 9.3 × 10-18 mol N2O per cell per hour (Figure 1D). After 120 h of growth, the N2O yield percentage from the added NO2- (100 μmol) was 5.1 ± 0.2% (5.1 ± 0.2 μmol) in the NMS + NO2- cultures.

Bottom Line: Aerobic methane-oxidizing bacteria (MOB) are a diverse group of microorganisms that are ubiquitous in natural environments.Along with anaerobic MOB and archaea, aerobic methanotrophs are critical for attenuating emission of methane to the atmosphere.Our results suggest that expression of denitrification genes, found widely within genomes of aerobic methanotrophs, allow the coupling of substrate oxidation to the reduction of nitrogen oxide terminal electron acceptors under oxygen limitation.

View Article: PubMed Central - PubMed

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

ABSTRACT
Aerobic methane-oxidizing bacteria (MOB) are a diverse group of microorganisms that are ubiquitous in natural environments. Along with anaerobic MOB and archaea, aerobic methanotrophs are critical for attenuating emission of methane to the atmosphere. Clearly, nitrogen availability in the form of ammonium and nitrite have strong effects on methanotrophic activity and their natural community structures. Previous findings show that nitrite amendment inhibits the activity of some cultivated methanotrophs; however, the physiological pathways that allow some strains to transform nitrite, expression of gene inventories, as well as the electron sources that support this activity remain largely uncharacterized. Here we show that Methylomicrobium album strain BG8 utilizes methane, methanol, formaldehyde, formate, ethane, ethanol, and ammonia to support denitrification activity under hypoxia only in the presence of nitrite. We also demonstrate that transcript abundance of putative denitrification genes, nirS and one of two norB genes, increased in response to nitrite. Furthermore, we found that transcript abundance of pxmA, encoding the alpha subunit of a putative copper-containing monooxygenase, increased in response to both nitrite and hypoxia. Our results suggest that expression of denitrification genes, found widely within genomes of aerobic methanotrophs, allow the coupling of substrate oxidation to the reduction of nitrogen oxide terminal electron acceptors under oxygen limitation. The present study expands current knowledge of the metabolic flexibility of methanotrophs by revealing that a diverse array of electron donors support nitrite reduction to nitrous oxide under hypoxia.

No MeSH data available.


Related in: MedlinePlus