The authors note that on page E1484, right column, first full paragraph, line 8, "the anaerobic oxidation of methane with sulfate (AOM) (1)" should instead appear as "the anaerobic oxidation of methane (AOM) with sulfate (1)."Also on page E1484, right column, Eq. 2 and its explanation appeared incorrectly. The corrected equation and its corrected explanation appear below.[2](Index e indicates activity ratio applying for equilibrium, viz. ΔG = 0; {H 2 O} is taken as 1) and thus one of the least exergonic processes sustaining life (ΔG in situ is often between −20 and −40 kJ mol −1 ) (21-23). On page E1485, right column, third full paragraph, lines 4-9, "If the subsequent reactions occur with reversibility and are viewed from the molecular perspective (that is, regarding microstates stochastically) at a given moment, the larger fraction of the enzyme molecules of each reaction performs the forward reaction, whereas a smaller fraction simultaneously performs the reverse reaction" should instead appear as "If subsequent reactions occur with reversibility and if the involved population of enzyme molecules is viewed from the molecular perspective (that is, regarding microstates stochastically) within a time interval in the range of an enzymatic turnover, the forward reaction is catalyzed more frequently than the reverse reaction."On page E1487, right column, Eq. 11 within the footnote appeared incorrectly. The corrected equation appears below. ∂Last, Fig. 3 appeared incorrectly. The corrected figure and its corresponding legend appear below. These errors do not affect the conclusions of the article.www.pnas.org/cgi/doi/10.1073/pnas.1218683109 Fig. 3. Depiction of forward and back flux during the net reaction A → P in a steady state catalytic system with reversible but otherwise unknown internal reactions. Such a system can consist of an entire pathway (A) or a single enzymatic reaction (B; E + A → EA → P + E) (Figs. S4 and S5). All reactions, including uptake or binding and release, are reversible. Arrows indicate rates (velocities). The forward (v + ) and back (v − ) rates correspond to individual steps in a catalytic system. The index n refers to the number of forward and backward fluxes (B; n = 2 for a single enzymatic reaction) (Fig. S5). A description of abbreviations is given in Table S3. (A) Catalytic system: the fate of substrate and product is followed by the different labels (A (Fig. S5) in a steady state (pools of A and P are essentially constant). The sizes of the rates are indicated by lengths of arrows. The same net rate (v) is the difference of uptake (binding) and release of substrate (v +1 , v −1 ) and product (v +2 , v −2 ) as well as the difference between forward and back flux (f + , f − ). The rate constants for the reaction steps (k +1 , k −1 , k +2 , k −2 ) and the actual concentrations of E, A, and P determine v +1 , v −1 , v +2 , v −2 , respectively, as indicated, and the resulting f + , and f − , which can only be revealed by labeling (Eqs. S35 and S36). The vector model was calculated for a...

Abstract:The recovery of natural gas from CH 4 -hydrate deposits in sub-marine and sub-permafrost environments through injection of CO 2 is considered a suitable strategy towards emission-neutral energy production. This study shows that the injection of hot, supercritical CO 2 is particularly promising. The addition of heat triggers the dissociation of CH 4 -hydrate while the CO 2 , once thermally equilibrated, reacts with the pore water and is retained in the reservoir as immobile CO 2 -hydrate. Furthermore, optimal reservoir conditions of pressure and temperature are constrained. Experiments were conducted in a high-pressure flow-through reactor at different sediment temperatures (2 °C, 8 °C, 10 °C) and hydrostatic pressures (8 MPa, 13 MPa). The efficiency of both, CH 4 production and CO 2 retention is best at 8 °C, 13 MPa. Here, both CO 2 -and CH 4 -hydrate as well as mixed hydrates can form. At 2 °C, the production process was less effective due to congestion of transport pathways through the sediment by rapidly forming CO 2 -hydrate. In contrast, at 10 °C CH 4 production suffered from local increases in permeability and fast breakthrough of the injection fluid, thereby confining the accessibility to the CH 4 pool to only the most prominent fluid channels. Mass and volume balancing of the collected gas and fluid stream identified gas mobilization as equally important process parameter in addition to the rates of methane hydrate dissociation and hydrate conversion. Thus, the combination of heat supply and CO 2 injection in one supercritical phase helps to overcome the mass transfer limitations usually observed in experiments with cold liquid or gaseous CO 2 .

Novel high-pressure biotechnical systems that were developed and applied for the study of anaerobic oxidation of methane (AOM) are described. The systems, referred to as high-pressure continuous incubation system (HP-CI system) and high-pressure manifold-incubation system (HP-MI system), allow for batch, fed-batch, and continuous gas-phase free incubation at high concentrations of dissolved methane and were designed to meet specific demands for studying environmental regulation and kinetics as well as for enriching microbial biomass in long-term incubation. Anoxic medium is saturated with methane in the first technical stage, and the saturated medium is supplied for biomass incubation in the second stage. Methane can be provided in continuous operation up to 20 MPa and the incubation systems can be operated during constant supply of gas-enriched medium at a hydrostatic pressure up to 45 MPa. To validate the suitability of the high-pressure systems, we present data from continuous and fed-batch incubation of highly active samples prepared from microbial mats from the Black Sea collected at a water depth of 213 m. In continuous operation in the HP-CI system initial methane-dependent sulfide production was enhanced 10- to 15-fold after increasing the methane partial pressure from near ambient pressure of 0.2 to 10.0 MPa at a hydrostatic pressure of 16.0 MPa in the incubation stage. With a hydraulic retention time of 14 h a stable effluent sulfide concentration was reached within less than 3 days and a continuing increase of the volumetric AOM rate from 1.2 to 1.7 mmol L(-1) day(-1) was observed over 14 days. In fed-batch incubation the AOM rate increased from 1.5 to 2.7 and 3.6 mmol L(-1) day(-1) when the concentration of aqueous methane was stepwise increased from 5 to 15 mmol L(-1) and 45 mmol L(-1). A methane partial pressure of 6 MPa and a hydrostatic pressure of 12 MPa in manifold fed-batch incubation in the HP-MI system yielded a sixfold increase in the volumetric AOM rate. Over subsequent incubation periods AOM rates increased from 0.6 to 1.2 mmol L(-1) day(-1) within 26 days of incubation. No inhibition of biomass activity was observed in all continuous and fed-batch incubation experiments. The organisms were able to tolerate high sulfide concentrations and extended starvation periods.