TY - JOUR
T1 - In situ hydrogen dynamics in a hot spring microbial mat during a diel cycle
AU - Revsbech, Niels Peter
AU - Trampe, Erik Christian Løvbjerg
AU - Lichtenberg, Mads
AU - Ward, David M.
AU - Kühl, Michael
PY - 2016
Y1 - 2016
N2 - Microbes can produce molecular hydrogen (H2) via fermentation, dinitrogen fixation, or direct photolysis, yet the H2 dynamics in cyanobacterial communities has only been explored in a few natural systems and mostly in the laboratory. In this study, we investigated the diel in situ H2 dynamics in a hot spring microbial mat, where various ecotypes of unicellular cyanobacteria (Synechococcus sp.) are the only oxygenic phototrophs. In the evening, H2 accumulated rapidly after the onset of darkness, reaching peak values of up to 30 μmol H2 liter-1 at about 1-mm depth below the mat surface, slowly decreasing to about 11 μmol H2 liter-1 just before sunrise. Another pulse of H2 production, reaching a peak concentration of 46 μmol H2 liter-1, was found in the early morning under dim light conditions too low to induce accumulation of O2 in the mat. The light stimulation of H2 accumulation indicated that nitrogenase activity was an important source of H2 during the morning. This is in accordance with earlier findings of a distinct early morning peak in N2 fixation and expression of Synechococcus nitrogenase genes in mat samples from the same location. Fermentation might have contributed to the formation of H2 during the night, where accumulation of other fermentation products lowered the pH in the mat to less than pH 6 compared to a spring source pH of 8.3.
AB - Microbes can produce molecular hydrogen (H2) via fermentation, dinitrogen fixation, or direct photolysis, yet the H2 dynamics in cyanobacterial communities has only been explored in a few natural systems and mostly in the laboratory. In this study, we investigated the diel in situ H2 dynamics in a hot spring microbial mat, where various ecotypes of unicellular cyanobacteria (Synechococcus sp.) are the only oxygenic phototrophs. In the evening, H2 accumulated rapidly after the onset of darkness, reaching peak values of up to 30 μmol H2 liter-1 at about 1-mm depth below the mat surface, slowly decreasing to about 11 μmol H2 liter-1 just before sunrise. Another pulse of H2 production, reaching a peak concentration of 46 μmol H2 liter-1, was found in the early morning under dim light conditions too low to induce accumulation of O2 in the mat. The light stimulation of H2 accumulation indicated that nitrogenase activity was an important source of H2 during the morning. This is in accordance with earlier findings of a distinct early morning peak in N2 fixation and expression of Synechococcus nitrogenase genes in mat samples from the same location. Fermentation might have contributed to the formation of H2 during the night, where accumulation of other fermentation products lowered the pH in the mat to less than pH 6 compared to a spring source pH of 8.3.
U2 - 10.1128/aem.00710-16
DO - 10.1128/aem.00710-16
M3 - Journal article
C2 - 27208140
SN - 0099-2240
VL - 82
SP - 4209
EP - 4217
JO - Applied and Environmental Microbiology
JF - Applied and Environmental Microbiology
IS - 14
ER -