Abstract
Monitoring in situ microbial activity in anoxic submerged soils and aquatic sediments can be labor intensive and technically difficult, especially in dynamic environments in which a record of changes in microbial activity over time is desired. Microbial fuel cell concepts have previously been adapted to detect changes in the availability of relatively high concentrations of organic compounds in waste water but, in most soils and sediments, rates of microbial activity are not linked to the concentrations of labile substrates, but rather to the turnover rates of the substrate pools with steady state concentrations in the nM–μM range. In order to determine whether levels of current produced at a graphite anode would correspond to the rates of microbial metabolism in anoxic sediments, small graphite anodes were inserted in sediment cores and connected to graphite brush cathodes in the overlying water. Currents produced were compared with the rates of [2-14C]-acetate metabolism. There was a direct correlation between current production and the rate that [2-14C]-acetate was metabolized to 14CO2 and 14CH4 in sediments in which Fe(III) reduction, sulfate reduction, or methane production was the predominant terminal electron-accepting process. At comparable acetate turnover rates, currents were higher in the sediments in which sulfate-reduction or Fe(III) reduction predominated than in methanogenic sediments. This was attributed to reduced products (Fe(II), sulfide) produced at distance from the anode contributing to current production in addition to the current that was produced from microbial oxidation of organic substrates with electron transfer to the anode surface in all three sediment types. The results demonstrate that inexpensive graphite electrodes may provide a simple strategy for real-time monitoring of microbial activity in a diversity of anoxic soils and sediments.
Highlights
Anaerobic microbial processes play an important role in the biogeochemistry of submerged soils and aquatic sediments, as well as in deeper subsurface environments (Yavitt et al, 1987; Canfield et al, 1993; Chapelle, 1993; Lovley and Chapelle, 1995; Liesack et al, 2000)
We demonstrate a direct correlation between current production and rates of microbial activity as determined by the turnover of tracer [2-14C]-acetate in sediments in which Fe(III) reduction, sulfate reduction, or methane production was the predominate terminal electron-accepting process
Frontiers in Microbiology | Microbial Physiology and Metabolism collected from sites at which Fe(III) reduction, sulfate reduction, or methane production was the predominant terminal electron accepting processes
Summary
Anaerobic microbial processes play an important role in the biogeochemistry of submerged soils and aquatic sediments, as well as in deeper subsurface environments (Yavitt et al, 1987; Canfield et al, 1993; Chapelle, 1993; Lovley and Chapelle, 1995; Liesack et al, 2000). The rate that all of these potential electron donors are produced from complex organic material near an anode inserted in anoxic soils and sediments should be reflected in the amount of current production.
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