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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

Dynamics of H2 and O2 concentration measured 0.6 mm below the surface of a coastal cyanobacterial mat in darkness and upon onset of illumination (500 μmol photons m-2 s-1).
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Figure 8: Dynamics of H2 and O2 concentration measured 0.6 mm below the surface of a coastal cyanobacterial mat in darkness and upon onset of illumination (500 μmol photons m-2 s-1).

Mentions: Simultaneous measurements of O2 and H2 concentration in the coastal mat at a depth of 0.6 mm, i.e., within the zone of maximal H2 production in the dark and photosynthetic O2 production in the light, showed pronounced dynamics (Figure 8). In the dark, O2 was depleted completely and H2 concentrations reached levels of 20–25 μM H2 after 15–20 min. However, immediately after onset of illumination we observed a burst in H2 production driving local concentrations up to 30–40 μM H2. This burst only lasted for 20–30 s, where after H2 became rapidly depleted as O2 from photosynthesis accumulated to super saturating concentration levels in the mat. Similar measurements (data not shown) in depth horizons closer to the mat surface showed a shorter and less intense burst due to more rapid O2 accumulation and thus faster H2 depletion, whereas measurement in deeper mat layers showed a less intense build-up of H2 upon onset of illumination due to strong light limitation; at 0.8 mm depth we observed no photo stimulation of H2 production. Such intermittent pulses of H2 upon illumination have been ascribed to direct biophotolysis in cyanobacteria involving a bidirectional Ni–Fe hydrogenase (Appel et al., 2000). While our data give first evidence that such biophotolysis can occur in the uppermost parts of cyanobacterial mats, the process is limited to <1 min after onset of illumination and thus plays a very minor role for the total H2 production.


Microsensor measurements of hydrogen gas dynamics in cyanobacterial microbial mats.

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

Dynamics of H2 and O2 concentration measured 0.6 mm below the surface of a coastal cyanobacterial mat in darkness and upon onset of illumination (500 μmol photons m-2 s-1).
© Copyright Policy
Related In: Results  -  Collection

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

Figure 8: Dynamics of H2 and O2 concentration measured 0.6 mm below the surface of a coastal cyanobacterial mat in darkness and upon onset of illumination (500 μmol photons m-2 s-1).
Mentions: Simultaneous measurements of O2 and H2 concentration in the coastal mat at a depth of 0.6 mm, i.e., within the zone of maximal H2 production in the dark and photosynthetic O2 production in the light, showed pronounced dynamics (Figure 8). In the dark, O2 was depleted completely and H2 concentrations reached levels of 20–25 μM H2 after 15–20 min. However, immediately after onset of illumination we observed a burst in H2 production driving local concentrations up to 30–40 μM H2. This burst only lasted for 20–30 s, where after H2 became rapidly depleted as O2 from photosynthesis accumulated to super saturating concentration levels in the mat. Similar measurements (data not shown) in depth horizons closer to the mat surface showed a shorter and less intense burst due to more rapid O2 accumulation and thus faster H2 depletion, whereas measurement in deeper mat layers showed a less intense build-up of H2 upon onset of illumination due to strong light limitation; at 0.8 mm depth we observed no photo stimulation of H2 production. Such intermittent pulses of H2 upon illumination have been ascribed to direct biophotolysis in cyanobacteria involving a bidirectional Ni–Fe hydrogenase (Appel et al., 2000). While our data give first evidence that such biophotolysis can occur in the uppermost parts of cyanobacterial mats, the process is limited to <1 min after onset of illumination and thus plays a very minor role for the total H2 production.

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