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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

Accumulation and depletion of H2 in a coastal cyanobacterial mat (same sample as in Figure 4) as a function of time after darkening. Measurements were performed 0.6 mm below the mat surface in the zone of maximal H2 production (see Figure 5).
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Figure 6: Accumulation and depletion of H2 in a coastal cyanobacterial mat (same sample as in Figure 4) as a function of time after darkening. Measurements were performed 0.6 mm below the mat surface in the zone of maximal H2 production (see Figure 5).

Mentions: The chemical conditions in the coastal mat changed dramatically after darkening (Figure 5). Within 5 min after darkening, O2 became strongly depleted and only penetrated ~0.3 mm into the mat, with a further decrease in the O2 penetration depth to 0.2 mm over the following 85 min. The O2 and H2S concentration profiles were initially separated by a ~0.7 mm wide zone, wherein H2 accumulated rapidly after darkening. Peak concentrations were measured 0.5–0.7 mm below the mat surface increasing from ~13 μM H2 after 5 min to ~22 μM H2 after 45 min dark incubation. Over this time interval, pH in the H2 production zone decreased to a stable value of pH 7.2–7.8. Produced H2 diffused both toward the mat surface and toward the sulfidic zone, where it was consumed. After 45 min, H2 levels in the mat started to decrease, while sulfide levels continued to increase in the upper mat layers. Sulfide started to overlap with the O2 concentration profile after 90 min. Hydrogen levels in the mat continued to decrease slowly and in a second experiment complete H2 depletion was only found after about 7 h dark incubation as seen in Figure 6, where data from continuous measurements at 0.6 mm depth are shown. The observed pattern of rapid build-up followed by a slow decline in H2 concentration follows a similar pattern observed in studies of H2 evolution in cyanobacterial isolates (Kothari et al., 2012).


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 (same sample as in Figure 4) as a function of time after darkening. Measurements were performed 0.6 mm below the mat surface in the zone of maximal H2 production (see Figure 5).
© Copyright Policy
Related In: Results  -  Collection

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

Figure 6: Accumulation and depletion of H2 in a coastal cyanobacterial mat (same sample as in Figure 4) as a function of time after darkening. Measurements were performed 0.6 mm below the mat surface in the zone of maximal H2 production (see Figure 5).
Mentions: The chemical conditions in the coastal mat changed dramatically after darkening (Figure 5). Within 5 min after darkening, O2 became strongly depleted and only penetrated ~0.3 mm into the mat, with a further decrease in the O2 penetration depth to 0.2 mm over the following 85 min. The O2 and H2S concentration profiles were initially separated by a ~0.7 mm wide zone, wherein H2 accumulated rapidly after darkening. Peak concentrations were measured 0.5–0.7 mm below the mat surface increasing from ~13 μM H2 after 5 min to ~22 μM H2 after 45 min dark incubation. Over this time interval, pH in the H2 production zone decreased to a stable value of pH 7.2–7.8. Produced H2 diffused both toward the mat surface and toward the sulfidic zone, where it was consumed. After 45 min, H2 levels in the mat started to decrease, while sulfide levels continued to increase in the upper mat layers. Sulfide started to overlap with the O2 concentration profile after 90 min. Hydrogen levels in the mat continued to decrease slowly and in a second experiment complete H2 depletion was only found after about 7 h dark incubation as seen in Figure 6, where data from continuous measurements at 0.6 mm depth are shown. The observed pattern of rapid build-up followed by a slow decline in H2 concentration follows a similar pattern observed in studies of H2 evolution in cyanobacterial isolates (Kothari et al., 2012).

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