Energetics of overall metabolic reactions of thermophilic and hyperthermophilic Archaea and Bacteria

Abstract

Thermophilic and hyperthermophilic Archaea and Bacteria have been isolated from marine hydrothermal systems, heated sediments, continental solfataras, hot springs, water heaters, and industrial waste. They catalyze a tremendous array of widely varying metabolic processes. As determined in the laboratory, electron donors in thermophilic and hyperthermophilic microbial redox reactions include H2, Fe(2+), H2S, S, S2O3(2-), S4O6(2-), sulfide minerals, CH4, various mono-, di-, and hydroxy-carboxylic acids, alcohols, amino acids, and complex organic substrates; electron acceptors include O2, Fe(3+), CO2, CO, NO3(-), NO2(-), NO, N2O, SO4(2-), SO3(2-), S2O3(2-), and S. Although many assimilatory and dissimilatory metabolic reactions have been identified for these groups of microorganisms, little attention has been paid to the energetics of these reactions. In this review, standard molal Gibbs free energies (DeltaGr(0)) as a function of temperature to 200 degrees C are tabulated for 370 organic and inorganic redox, disproportionation, dissociation, hydrolysis, and solubility reactions directly or indirectly involved in microbial metabolism. To calculate values of DeltaGr(0) for these and countless other reactions, the apparent standard molal Gibbs free energies of formation (DeltaG(0)) at temperatures to 200 degrees C are given for 307 solids, liquids, gases, and aqueous solutes. It is shown that values of DeltaGr(0) for many microbially mediated reactions are highly temperature dependent, and that adopting values determined at 25 degrees C for systems at elevated temperatures introduces significant and unnecessary errors. The metabolic processes considered here involve compounds that belong to the following chemical systems: H-O, H-O-N, H-O-S, H-O-N-S, H-O-C(inorganic), H-O-C, H-O-N-C, H-O-S-C, H-O-N-S-C(amino acids), H-O-S-C-metals/minerals, and H-O-P. For four metabolic reactions of particular interest in thermophily and hyperthermophily (knallgas reaction, anaerobic sulfur and nitrate reduction, and autotrophic methanogenesis), values of the overall Gibbs free energy (DeltaGr) as a function of temperature are calculated for a wide range of chemical compositions likely to be present in near-surface and deep hydrothermal and geothermal systems.

Comparative Study of Guaymas Basin Microbiomes: Cold Seeps vs. Hydrothermal Vents Sediments

“…Supporting the positive correlation between these lineages and the temperatures measured in the sediments (Figure 5 and Figure S1), cultivated representatives of these lineages are thermophiles, growing at temperatures from 50 to 90 • C (Amend and Shock, 2001). A higher level of endemism was detected in the deepest microbial mat sediment layers where the highest in situ temperatures were measured, as previously reported (Mackay et al, 2011).…”

Molecular evidence of Late Archean archaea and the presence of a subsurface hydrothermal biosphere

“…A bacterial and archaeal subsurface biosphere now is believed to have a near-global extent, being found in marine sediments; in the fractures and vents near midoceanic spreading centers; within older, cooled basaltic crust beneath the oceans; in deep aquifers of basalts and granitic batholiths; and in deep oil reservoirs of continental settings (51)(52)(53). Our results provide molecular fossil evidence for the existence of archaea in Late Archean sedimentary environments and in subsurface hydrothermal settings.…”

“…Based on the solubility of Au-(HS) Ϫ , gold precipitation is thought to have occurred at cooler temperatures and/or lower pressure (49). The envelope of cooled, high sulfur and reduced, carbon-rich fluids surrounding this region of high heat flow would provide favorable conditions for hyperthermophilic communities of archaea and bacteria (50,51). Continued burial likely would convert a subsurface biosphere's biomass into the observed secondary addition of hydrocarbons (Fig.…”

BIOSIGNATURE GASES IN H2-DOMINATED ATMOSPHERES ON ROCKY EXOPLANETS

“…Reactant and product concentrations can include ocean pH (concentration of H + ) in reactions that generate or consume protons. ΔG 0 values are taken from Amend & Shock (2001). The term P m e is an empirically determined microbial maintenance energy consumption rate that is the minimum amount of energy an organism needs per unit time to survive in an active state (i.e., a state in which the organism is ready to grow).…”