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Microsensor measurements of hydrogen gas dynamics in cyanobacterial microbial mats.

Nielsen M, Revsbech NP, Kühl M - Front Microbiol (2015)

Bottom Line: Depletion could be prevented by addition of molybdate pointing to sulfate reduction as a major sink for H2.As soon as O2 from photosynthesis started to accumulate, the H2 was consumed rapidly and production ceased.Our data give detailed insights into the microscale distribution and dynamics of H2 in cyanobacterial biofilms and mats, and further support that cyanobacterial H2 production can play a significant role in fueling anaerobic processes like e.g., sulfate reduction or anoxygenic photosynthesis in microbial mats.

View Article: PubMed Central - PubMed

Affiliation: Section of Microbiology, Department of Bioscience, Aarhus University Aarhus, Denmark.

ABSTRACT
We used a novel amperometric microsensor for measuring hydrogen gas production and consumption at high spatio-temporal resolution in cyanobacterial biofilms and mats dominated by non-heterocystous filamentous cyanobacteria (Microcoleus chtonoplastes and Oscillatoria sp.). The new microsensor is based on the use of an organic electrolyte and a stable internal reference system and can be equipped with a chemical sulfide trap in the measuring tip; it exhibits very stable and sulfide-insensitive measuring signals and a high sensitivity (1.5-5 pA per μmol L(-1) H2). Hydrogen gas measurements were done in combination with microsensor measurements of scalar irradiance, O2, pH, and H2S and showed a pronounced H2 accumulation (of up to 8-10% H2 saturation) within the upper mm of cyanobacterial mats after onset of darkness and O2 depletion. The peak concentration of H2 increased with the irradiance level prior to darkening. After an initial build-up over the first 1-2 h in darkness, H2 was depleted over several hours due to efflux to the overlaying water, and due to biogeochemical processes in the uppermost oxic layers and the anoxic layers of the mats. Depletion could be prevented by addition of molybdate pointing to sulfate reduction as a major sink for H2. Immediately after onset of illumination, a short burst of presumably photo-produced H2 due to direct biophotolysis was observed in the illuminated but anoxic mat layers. As soon as O2 from photosynthesis started to accumulate, the H2 was consumed rapidly and production ceased. Our data give detailed insights into the microscale distribution and dynamics of H2 in cyanobacterial biofilms and mats, and further support that cyanobacterial H2 production can play a significant role in fueling anaerobic processes like e.g., sulfate reduction or anoxygenic photosynthesis in microbial mats.

No MeSH data available.


Related in: MedlinePlus

Concentration profiles of O2(A) and H2(B) in a hypersaline microbial mat measured after 2.5 h under a photon irradiance of 800 μmol photons m-2 s-1 and as a function of time after darkening.
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Figure 1: Concentration profiles of O2(A) and H2(B) in a hypersaline microbial mat measured after 2.5 h under a photon irradiance of 800 μmol photons m-2 s-1 and as a function of time after darkening.

Mentions: When incubated under an irradiance of 800 μmol photons m-2 s-1 for 2.5 h, intense photosynthesis in the dense 2–3 mm thick hypersaline cyanobacterial biofilm lead to hyperoxic conditions reaching 4–5 times air saturation in the upper mm and supersaturating O2 levels throughout the whole sample, which was contained in a small glass container (Figure 1A). Upon darkening, O2 was most rapidly depleted in the region showing highest O2 production activity in light, and H2 was first detected in this zone after 15 min. As O2 became further depleted, H2 accumulated to higher concentrations and over a wider zone in the biofilm reaching a maximum of 8 μmol H2 L-1 (~1.6% H2) at 1 mm depth after 2 h in the dark. Hydrogen was consumed in the lowermost parts of the biofilm sample, which was constrained by the bottom of the small glass incubation container. The apparent migration of the H2 peak into slightly deeper layers probably reflects a shift in the relative balance between H2 production, consumption and transport, especially as the mat sample was confined in a small glass vial presenting a diffusion barrier ~4 mm below the mat surface.


Microsensor measurements of hydrogen gas dynamics in cyanobacterial microbial mats.

Nielsen M, Revsbech NP, Kühl M - Front Microbiol (2015)

Concentration profiles of O2(A) and H2(B) in a hypersaline microbial mat measured after 2.5 h under a photon irradiance of 800 μmol photons m-2 s-1 and as a function of time after darkening.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4508582&req=5

Figure 1: Concentration profiles of O2(A) and H2(B) in a hypersaline microbial mat measured after 2.5 h under a photon irradiance of 800 μmol photons m-2 s-1 and as a function of time after darkening.
Mentions: When incubated under an irradiance of 800 μmol photons m-2 s-1 for 2.5 h, intense photosynthesis in the dense 2–3 mm thick hypersaline cyanobacterial biofilm lead to hyperoxic conditions reaching 4–5 times air saturation in the upper mm and supersaturating O2 levels throughout the whole sample, which was contained in a small glass container (Figure 1A). Upon darkening, O2 was most rapidly depleted in the region showing highest O2 production activity in light, and H2 was first detected in this zone after 15 min. As O2 became further depleted, H2 accumulated to higher concentrations and over a wider zone in the biofilm reaching a maximum of 8 μmol H2 L-1 (~1.6% H2) at 1 mm depth after 2 h in the dark. Hydrogen was consumed in the lowermost parts of the biofilm sample, which was constrained by the bottom of the small glass incubation container. The apparent migration of the H2 peak into slightly deeper layers probably reflects a shift in the relative balance between H2 production, consumption and transport, especially as the mat sample was confined in a small glass vial presenting a diffusion barrier ~4 mm below the mat surface.

Bottom Line: Depletion could be prevented by addition of molybdate pointing to sulfate reduction as a major sink for H2.As soon as O2 from photosynthesis started to accumulate, the H2 was consumed rapidly and production ceased.Our data give detailed insights into the microscale distribution and dynamics of H2 in cyanobacterial biofilms and mats, and further support that cyanobacterial H2 production can play a significant role in fueling anaerobic processes like e.g., sulfate reduction or anoxygenic photosynthesis in microbial mats.

View Article: PubMed Central - PubMed

Affiliation: Section of Microbiology, Department of Bioscience, Aarhus University Aarhus, Denmark.

ABSTRACT
We used a novel amperometric microsensor for measuring hydrogen gas production and consumption at high spatio-temporal resolution in cyanobacterial biofilms and mats dominated by non-heterocystous filamentous cyanobacteria (Microcoleus chtonoplastes and Oscillatoria sp.). The new microsensor is based on the use of an organic electrolyte and a stable internal reference system and can be equipped with a chemical sulfide trap in the measuring tip; it exhibits very stable and sulfide-insensitive measuring signals and a high sensitivity (1.5-5 pA per μmol L(-1) H2). Hydrogen gas measurements were done in combination with microsensor measurements of scalar irradiance, O2, pH, and H2S and showed a pronounced H2 accumulation (of up to 8-10% H2 saturation) within the upper mm of cyanobacterial mats after onset of darkness and O2 depletion. The peak concentration of H2 increased with the irradiance level prior to darkening. After an initial build-up over the first 1-2 h in darkness, H2 was depleted over several hours due to efflux to the overlaying water, and due to biogeochemical processes in the uppermost oxic layers and the anoxic layers of the mats. Depletion could be prevented by addition of molybdate pointing to sulfate reduction as a major sink for H2. Immediately after onset of illumination, a short burst of presumably photo-produced H2 due to direct biophotolysis was observed in the illuminated but anoxic mat layers. As soon as O2 from photosynthesis started to accumulate, the H2 was consumed rapidly and production ceased. Our data give detailed insights into the microscale distribution and dynamics of H2 in cyanobacterial biofilms and mats, and further support that cyanobacterial H2 production can play a significant role in fueling anaerobic processes like e.g., sulfate reduction or anoxygenic photosynthesis in microbial mats.

No MeSH data available.


Related in: MedlinePlus