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A 'rare biosphere' microorganism contributes to sulfate reduction in a peatland.

Pester M, Bittner N, Deevong P, Wagner M, Loy A - ISME J (2010)

Bottom Line: Methane emission from peatlands contributes substantially to global warming but is significantly reduced by sulfate reduction, which is fuelled by globally increasing aerial sulfur pollution.For the identified Desulfosporosinus species a high cell-specific sulfate reduction rate of up to 341 fmol SO₄²⁻ cell⁻¹ day⁻¹ was estimated.Thus, the small Desulfosporosinus population has the potential to reduce sulfate in situ at a rate of 4.0-36.8 nmol (g soil w. wt.)⁻¹ day⁻¹, sufficient to account for a considerable part of sulfate reduction in the peat soil.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbial Ecology, University of Vienna, Wien, Austria.

ABSTRACT
Methane emission from peatlands contributes substantially to global warming but is significantly reduced by sulfate reduction, which is fuelled by globally increasing aerial sulfur pollution. However, the biology behind sulfate reduction in terrestrial ecosystems is not well understood and the key players for this process as well as their abundance remained unidentified. Comparative 16S rRNA gene stable isotope probing (SIP) in the presence and absence of sulfate indicated that a Desulfosporosinus species, which constitutes only 0.006% of the total microbial community 16S rRNA genes, is an important sulfate reducer in a long-term experimental peatland field site. Parallel SIP using dsrAB (encoding subunit A and B of the dissimilatory (bi)sulfite reductase) identified no additional sulfate reducers under the conditions tested. For the identified Desulfosporosinus species a high cell-specific sulfate reduction rate of up to 341 fmol SO₄²⁻ cell⁻¹ day⁻¹ was estimated. Thus, the small Desulfosporosinus population has the potential to reduce sulfate in situ at a rate of 4.0-36.8 nmol (g soil w. wt.)⁻¹ day⁻¹, sufficient to account for a considerable part of sulfate reduction in the peat soil. Modeling of sulfate diffusion to such highly active cells identified no limitation in sulfate supply even at bulk concentrations as low as 10 μM. Collectively, these data show that the identified Desulfosporosinus species, despite being a member of the 'rare biosphere', contributes to an important biogeochemical process that diverts the carbon flow in peatlands from methane to CO₂ and, thus, alters their contribution to global warming.

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Substrate and sulfate measurements during pre-incubation and 12C-substrate turnover determinations. (A) Monitoring of indigenous substrate and sulfate concentrations during 4 weeks of pre-incubation of anoxic non-amended peat soil slurries. Averages ± SD are shown (n=6). (B) Time course of 12C-substrate turnover in anoxic peat soil slurries in the presence and absence of sulfate. Arrows indicate the time points of substrate additions; sulfate was added only once at the beginning of the experiment. Data points represent average values of three independent soil slurries; standard deviation bars were omitted for better visibility.
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Figure 1: Substrate and sulfate measurements during pre-incubation and 12C-substrate turnover determinations. (A) Monitoring of indigenous substrate and sulfate concentrations during 4 weeks of pre-incubation of anoxic non-amended peat soil slurries. Averages ± SD are shown (n=6). (B) Time course of 12C-substrate turnover in anoxic peat soil slurries in the presence and absence of sulfate. Arrows indicate the time points of substrate additions; sulfate was added only once at the beginning of the experiment. Data points represent average values of three independent soil slurries; standard deviation bars were omitted for better visibility.

Mentions: Six anoxic peat soil slurries were pre-incubated at 14°C for 28 days. Electron acceptors such as nitrate, sulfate, and iron(III) are typically reduced after 16 days in Schlöppnerbrunnen II peat soil slurries (Küsel et al., 2008), which is an important prerequisite for selective labeling. During this pre-incubation, lactate, acetate, and formate stayed in the lower μM-range (<20 μM) while propionate accumulated transiently up to 155 μM in individual slurries. Initial sulfate concentrations were 22 μM and dropped thereafter below 4 μM (Fig. 1A). After pre-incubation, an unlabelled substrate mix of lactate, acetate, formate, and propionate (50–200 μM each) was added twice over a period of two weeks to all soil slurries to determine the time needed for substrate depletion. In addition, three of the six soil slurries were supplemented once with 100–200 μM sulfate. In all incubations, lactate and formate were readily turned over within two days, while acetate and propionate needed four and six days for turnover after the first and second substrate addition, respectively (Fig. 1B, Table 1). Thereafter, soil slurries were incubated without any additions for 17 days to allow for complete depletion of added 12C-substrates. After this post-incubation, the headspace of each mesocosm was flushed with 100% N2 to remove accumulated 12CO2 and the actual SIP incubations were started (pre-incubations and subsequent SIP incubations are detailed in Fig. S2).


A 'rare biosphere' microorganism contributes to sulfate reduction in a peatland.

Pester M, Bittner N, Deevong P, Wagner M, Loy A - ISME J (2010)

Substrate and sulfate measurements during pre-incubation and 12C-substrate turnover determinations. (A) Monitoring of indigenous substrate and sulfate concentrations during 4 weeks of pre-incubation of anoxic non-amended peat soil slurries. Averages ± SD are shown (n=6). (B) Time course of 12C-substrate turnover in anoxic peat soil slurries in the presence and absence of sulfate. Arrows indicate the time points of substrate additions; sulfate was added only once at the beginning of the experiment. Data points represent average values of three independent soil slurries; standard deviation bars were omitted for better visibility.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4499578&req=5

Figure 1: Substrate and sulfate measurements during pre-incubation and 12C-substrate turnover determinations. (A) Monitoring of indigenous substrate and sulfate concentrations during 4 weeks of pre-incubation of anoxic non-amended peat soil slurries. Averages ± SD are shown (n=6). (B) Time course of 12C-substrate turnover in anoxic peat soil slurries in the presence and absence of sulfate. Arrows indicate the time points of substrate additions; sulfate was added only once at the beginning of the experiment. Data points represent average values of three independent soil slurries; standard deviation bars were omitted for better visibility.
Mentions: Six anoxic peat soil slurries were pre-incubated at 14°C for 28 days. Electron acceptors such as nitrate, sulfate, and iron(III) are typically reduced after 16 days in Schlöppnerbrunnen II peat soil slurries (Küsel et al., 2008), which is an important prerequisite for selective labeling. During this pre-incubation, lactate, acetate, and formate stayed in the lower μM-range (<20 μM) while propionate accumulated transiently up to 155 μM in individual slurries. Initial sulfate concentrations were 22 μM and dropped thereafter below 4 μM (Fig. 1A). After pre-incubation, an unlabelled substrate mix of lactate, acetate, formate, and propionate (50–200 μM each) was added twice over a period of two weeks to all soil slurries to determine the time needed for substrate depletion. In addition, three of the six soil slurries were supplemented once with 100–200 μM sulfate. In all incubations, lactate and formate were readily turned over within two days, while acetate and propionate needed four and six days for turnover after the first and second substrate addition, respectively (Fig. 1B, Table 1). Thereafter, soil slurries were incubated without any additions for 17 days to allow for complete depletion of added 12C-substrates. After this post-incubation, the headspace of each mesocosm was flushed with 100% N2 to remove accumulated 12CO2 and the actual SIP incubations were started (pre-incubations and subsequent SIP incubations are detailed in Fig. S2).

Bottom Line: Methane emission from peatlands contributes substantially to global warming but is significantly reduced by sulfate reduction, which is fuelled by globally increasing aerial sulfur pollution.For the identified Desulfosporosinus species a high cell-specific sulfate reduction rate of up to 341 fmol SO₄²⁻ cell⁻¹ day⁻¹ was estimated.Thus, the small Desulfosporosinus population has the potential to reduce sulfate in situ at a rate of 4.0-36.8 nmol (g soil w. wt.)⁻¹ day⁻¹, sufficient to account for a considerable part of sulfate reduction in the peat soil.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbial Ecology, University of Vienna, Wien, Austria.

ABSTRACT
Methane emission from peatlands contributes substantially to global warming but is significantly reduced by sulfate reduction, which is fuelled by globally increasing aerial sulfur pollution. However, the biology behind sulfate reduction in terrestrial ecosystems is not well understood and the key players for this process as well as their abundance remained unidentified. Comparative 16S rRNA gene stable isotope probing (SIP) in the presence and absence of sulfate indicated that a Desulfosporosinus species, which constitutes only 0.006% of the total microbial community 16S rRNA genes, is an important sulfate reducer in a long-term experimental peatland field site. Parallel SIP using dsrAB (encoding subunit A and B of the dissimilatory (bi)sulfite reductase) identified no additional sulfate reducers under the conditions tested. For the identified Desulfosporosinus species a high cell-specific sulfate reduction rate of up to 341 fmol SO₄²⁻ cell⁻¹ day⁻¹ was estimated. Thus, the small Desulfosporosinus population has the potential to reduce sulfate in situ at a rate of 4.0-36.8 nmol (g soil w. wt.)⁻¹ day⁻¹, sufficient to account for a considerable part of sulfate reduction in the peat soil. Modeling of sulfate diffusion to such highly active cells identified no limitation in sulfate supply even at bulk concentrations as low as 10 μM. Collectively, these data show that the identified Desulfosporosinus species, despite being a member of the 'rare biosphere', contributes to an important biogeochemical process that diverts the carbon flow in peatlands from methane to CO₂ and, thus, alters their contribution to global warming.

Show MeSH
Related in: MedlinePlus