Hydrogen Dynamics in Cyanobacteria Dominated Microbial Mats Measured by Novel Combined H2/H2S and H2/O2 Microsensors

Abstract

Hydrogen may accumulate to micromolar concentrations in cyanobacterial mat communities from various environments, but the governing factors for this accumulation are poorly described. We used newly developed sensors allowing for simultaneous measurement of H2S and H2 or O2 and H2 within the same point to elucidate the interactions between oxygen, sulfate reducing bacteria, and H2 producing microbes. After onset of darkness and subsequent change from oxic to anoxic conditions within the uppermost ∼1 mm of the mat, H2 accumulated to concentrations of up to 40 μmol L-1 in the formerly oxic layer, but with high variability among sites and sampling dates. The immediate onset of H2 production after darkening points to fermentation as the main H2 producing process in this mat. The measured profiles indicate that a gradual disappearance of the H2 peak was mainly due to the activity of sulfate reducing bacteria that invaded the formerly oxic surface layer from below, or persisted in an inactive state in the oxic mat during illumination. The absence of significant H2 consumption in the formerly oxic mat during the first ∼30 min after onset of anoxic conditions indicated absence of active sulfate reducers in this layer during the oxic period. Addition of the methanogenesis inhibitor BES led to increase in H2, indicating that methanogens contributed to the consumption of H2. Both H2 formation and consumption seemed unaffected by the presence/absence of H2S.

Considerations on the use of microsensors to profile dissolved H2 concentrations in microbial electrochemical reactors

“…Moreover, H 2 microsensors are sensitive (detection limit generally < 1 μM), fast responding (response time of a few seconds), highly accurate and almost non-invasive [14,15]. Microsensors for H 2 have been used for many years to study different natural environments on a microscale [16,17]. Since bioelectrochemical and other biotechnologies are nowadays intensively being studied, H 2 microsensors are also being used to obtain insights into engineered systems [8,[18][19][20][21][22].…”

Community homeostasis of coastal microbial mats from the Camargue during winter (cold) and summer (hot) seasons

“…Migratory rhythms determined by day/night cycles, UV exposure and changes in irradiance levels have been described for both microalgae and cyanobacteria‐dominated phototrophic mat communities (Haro et al, 2019; Lichtenberg et al, 2020). During the night, due to a continuing sulfate reduction in the absence of oxygenic photosynthesis, the mats changed to anoxic conditions and with high hydrogen sulfide concentration (Maegaard et al, 2017; Nielsen et al, 2015). Daily variations, such as the day – night cycle, are thought to have little influence on the composition of coastal microbial mat communities, although they may enhance or suppress the metabolic activity of different populations (Campbell et al, 2020; Haro et al, 2019).…”

From two sensors to a single sensor: Better understanding of oxygen–sulfide interfaces

“…In this study, we show how the problem of difficult alignment of microsensors for the study of H 2 S oxidation can be solved. It has earlier been shown that a single sensor can be used for simultaneous and spatially coincident measurement of O 2 /N 2 O (Revsbech et al 1988), H 2 /O 2 (Maegaard et al 2017), and H 2 /H 2 S (Maegaard et al 2018). We here expand this range of combined sensors with a sensor for measuring H 2 S and O 2 .…”