Limits...
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

Accumulation and depletion of H2 in a coastal cyanobacterial mat as a function of time after darkening (see numbers and color legends in the graph). Prior to darkening, the mat was incubated under a photon irradiance of 500 μmol photons m-2 s-1 in aerated seawater for 8 h without (A,B) and for 6 h with 2.5 mM molybdate (C). Note the use of different concentration ranges in the different panels.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4508582&req=5

Figure 7: Accumulation and depletion of H2 in a coastal cyanobacterial mat as a function of time after darkening (see numbers and color legends in the graph). Prior to darkening, the mat was incubated under a photon irradiance of 500 μmol photons m-2 s-1 in aerated seawater for 8 h without (A,B) and for 6 h with 2.5 mM molybdate (C). Note the use of different concentration ranges in the different panels.

Mentions: Additional measurements of H2 production after onset of darkness were done in another coastal mat sample from the same habitat (Figure 7) that was incubated 8 h under a photon irradiance of 500 μmol photons m-2 s-1 prior to darkening. When incubated in normal seawater, the mat reached maximal concentrations of ~18 μM H2 at 0.5–0.7 mm depth within 60 min after darkening, where after H2 levels in the mat declined gradually to ~1.5 μM H2 after 720 min in darkness (Figures 7A,B). Thereafter, the same mat was incubated 6 h under a photon irradiance of 500 μmol photons m-2 s-1 in seawater with 2.5 mM molybdate, an inhibitor of sulfate reduction. Measurements in light at the end of this incubation showed a similar O2 and pH distribution, whereas H2S levels in the mat were much lower below the photic zone than in the absence of molybdate (Supplementary Figures S3 and S5); interestingly, a slight accumulation of H2 (reaching 1–1.5 μM) was also observed in deeper mat layers around 3 mm depth after the molybdate treatment, i.e., in the aphotic zone that exhibited high H2S levels in the absence of molybdate.


Microsensor measurements of hydrogen gas dynamics in cyanobacterial microbial mats.

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

Accumulation and depletion of H2 in a coastal cyanobacterial mat as a function of time after darkening (see numbers and color legends in the graph). Prior to darkening, the mat was incubated under a photon irradiance of 500 μmol photons m-2 s-1 in aerated seawater for 8 h without (A,B) and for 6 h with 2.5 mM molybdate (C). Note the use of different concentration ranges in the different panels.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 7: Accumulation and depletion of H2 in a coastal cyanobacterial mat as a function of time after darkening (see numbers and color legends in the graph). Prior to darkening, the mat was incubated under a photon irradiance of 500 μmol photons m-2 s-1 in aerated seawater for 8 h without (A,B) and for 6 h with 2.5 mM molybdate (C). Note the use of different concentration ranges in the different panels.
Mentions: Additional measurements of H2 production after onset of darkness were done in another coastal mat sample from the same habitat (Figure 7) that was incubated 8 h under a photon irradiance of 500 μmol photons m-2 s-1 prior to darkening. When incubated in normal seawater, the mat reached maximal concentrations of ~18 μM H2 at 0.5–0.7 mm depth within 60 min after darkening, where after H2 levels in the mat declined gradually to ~1.5 μM H2 after 720 min in darkness (Figures 7A,B). Thereafter, the same mat was incubated 6 h under a photon irradiance of 500 μmol photons m-2 s-1 in seawater with 2.5 mM molybdate, an inhibitor of sulfate reduction. Measurements in light at the end of this incubation showed a similar O2 and pH distribution, whereas H2S levels in the mat were much lower below the photic zone than in the absence of molybdate (Supplementary Figures S3 and S5); interestingly, a slight accumulation of H2 (reaching 1–1.5 μM) was also observed in deeper mat layers around 3 mm depth after the molybdate treatment, i.e., in the aphotic zone that exhibited high H2S levels in the absence of molybdate.

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