Apparent minimum free energy requirements for methanogenic Archaea and sulfate-reducing bacteria in an anoxic marine sediment

Abstract

Among the most fundamental constraints governing the distribution of microorganisms in the environment is the availability of chemical energy at biologically useful levels. To assess the minimum free energy yield that can support microbial metabolism in situ, we examined the thermodynamics of H2‐consuming processes in anoxic sediments from Cape Lookout Bight, NC, USA. Depth distributions of H2 partial pressure, along with a suite of relevant concentration data, were determined in sediment cores collected in November (at 14.5°C) and August (at 27°C) and used to calculate free energy yields for methanogenesis and sulfate reduction. At both times of year, and for both processes, free energy yields gradually decreased (became less negative) with depth before reaching an apparent asymptote. Sulfate‐reducing bacteria exhibited an asymptote of −19.1±1.7 kJ (mol SO2−4)−1, while methanogenic Archaea were apparently supported by energy yields as small as −10.6±0.7 kJ (mol CH4)−1.

Considering a Threshold Energy in Reactive Transport Modeling of Microbially Mediated Redox Reactions in an Arsenic-Affected Aquifer

“…These results are consistent with literature values, such as 11.8 kJ/mol e − for Fe-oxide reduction [29], 4.9 [29] and 2.4 [31] kJ/mol e − for sulfate reduction, and 2.7 [29] and 1.3 [31] kJ/mol e − for methanogenesis. That these threshold energy values are quite close and quite small indicates that the simpler "partial equilibrium" approach to modeling anaerobic redox processes is also viable.…”

“…The difference between the logK and the shifted logK in terms of Gibbs energy is the threshold energy, that is, in other words, the energy required in the system to make the reaction microbiologically feasible. Along the lines of Hoehler [31], followed by subsequent works [28,29], who proposed that the H 2 level may reflect the internal redox state of many different types of anaerobic microorganisms, regardless of the main electron donor used, TEAP reactions were rewritten in the PHREEQC database considering the H 2 as the reductant instead of electrons. This also enables a comparison of results with previous works [28,29,31], as well as checking if the modeled H 2 levels are reasonable compared to values typical for natural systems.…”

“…Only a few studies considered the role of bacteria in mediating reactions in reactive transport modeling [28][29][30], through the implementation of a threshold energy for the occurrence of TEAPs [28,29]. This threshold energy represents the minimum Gibbs energy required by bacteria to conduct the reaction [31,32], in order to sustain their life functions. Jakobsen and Cold [29] considered a threshold energy for TEAPs in unidirectional reactions, whereas Jakobsen [28] improved this approach by implementing a threshold energy on both reaction direction for the redox reaction pair methanogenesis/methane oxidation.…”

Temporal evolution of methane cycling and phylogenetic diversity of archaea in sediments from a deep-sea whale-fall in Monterey Canyon, California

“…Pathways of organic carbon remineralization: the role of hydrogen Molecular hydrogen is an important energy source for the anaerobic biodegradation of organic materials (Reeve et al, 1997;Hoehler et al, 2001). Methanogenesis could, in theory, co-occur with sulfate reduction if there was an abundance of competitive substrates, such as hydrogen or acetate.…”

Cultivation-Based Characterization of Microbial Communities Associated with Deep Sedimentary Rocks from Taiwan Chelungpu Drilling Project Cores

“…The competition for organic acids or H 2 , therefore, regulates the distribution of each terminal electron accepting process and geochemical characteristics along the groundwater flow path. Metabolic reaction with more free energy yield decreases organic acids or H 2 to a threshold level below which other metabolic reactions with less free energy yield would not be able to acquire enough substrate for minimum maintenance (Hoehler et al 2001). Instead of being electron donor (presumably organic carbon) limited, the deep subsurface ecosystem might be limited by electron acceptors (Fredrickson and Onstott 2001).…”