Biological methane production under putative Enceladus-like conditions.

The detection of silica-rich dust particles, as an indication for ongoing hydrothermal activity, and the presence of water and organic molecules in the plume of Enceladus, have made Saturn's icy moon a hot spot in the search for potential extraterrestrial life. Methanogenic archaea are among the organisms that could potentially thrive under the predicted conditions on Enceladus, considering that both molecular hydrogen (H2) and methane (CH4) have been detected in the plume. Here we show that a methanogenic archaeon, Methanothermococcus okinawensis, can produce CH4 under physicochemical conditions extrapolated for Enceladus. Up to 72% carbon dioxide to CH4 conversion is reached at 50 bar in the presence of potential inhibitors. Furthermore, kinetic and thermodynamic computations of low-temperature serpentinization indicate that there may be sufficient H2 gas production to serve as a substrate for CH4 production on Enceladus. We conclude that some of the CH4 detected in the plume of Enceladus might, in principle, be produced by methanogens.

Profiling of Indigenous Microbial Community Dynamics and Metabolic Activity During Enrichment in Molasses-Supplemented Crude Oil-Brine Mixtures for Improved Understanding of Microbial Enhanced Oil Recovery.

Anaerobic incubations using crude oil and brine from a North Sea reservoir were conducted to gain increased understanding of indigenous microbial community development, metabolite production, and the effects on the oil-brine system after addition of a complex carbon source, molasses, with or without nitrate to boost microbial growth. Growth of the indigenous microbes was stimulated by addition of molasses. Pyrosequencing showed that specifically Anaerobaculum, Petrotoga, and Methanothermococcus were enriched. Addition of nitrate favored the growth of Petrotoga over Anaerobaculum. The microbial growth caused changes in the crude oil-brine system: formation of oil emulsions, and reduction of interfacial tension (IFT). Reduction in IFT was associated with microbes being present at the oil-brine interphase. These findings suggest that stimulation of indigenous microbial growth by addition of molasses has potential as microbial enhanced oil recovery (MEOR) strategy in North Sea oil reservoirs.

Growth of methanogens under defined hydrogen conditions.

Hydrogen (H(2)) is a primary electron donor for methanogenesis and its availability can have profound effects on gene expression and the physiology of energy conservation. The rigorous evaluation of the effects of hydrogen conditions requires the comparison of cultures that are grown under hydrogen limitation and hydrogen excess. The growth of methanogens under defined hydrogen conditions is complicated by the dynamics of hydrogen dissolution and its utilization by the cells. In batch culture, gassing and agitation conditions must be carefully calibrated, and even then variations in growth rate and cell density are hard to avoid. Using chemostats, continuous cultures can be achieved whose nutritional states are known, while growth rate and cell density are invariant. Cultures whose growth is limited by hydrogen can be compared to cultures whose growth is limited by some other nutrient and are therefore under hydrogen excess.

Transcriptional responses of the deep-sea hyperthermophile Methanocaldococcus jannaschii under shifting extremes of temperature and pressure.

Growth and transcriptional profiles of the deep-sea methanarchaeon Methanocaldococcus jannaschii were studied under sudden up-shifts of temperature and pressure. Application of 500 atm of hyperbaric pressure shifted the optimal growth temperature upwards by about 5 degrees C in a high temperature-pressure bioreactor, and increased the specific growth rate threefold at 88 degrees C. In contrast, pressure-shock from 7.8 to 500 atm over 15 min, the first such pressure up-shift reported for a piezophile, did not accelerate growth. High-pressure heat-shock from 88 to 98 degrees C, a condition relevant to the turbulent in situ surroundings of deep-sea hydrothermal vents, resulted in termination of growth. Transcriptional profiles for cells grown at 88 degrees C and 500 atm, heat-shocked at 500 atm, and pressure-shocked to 500 atm, shared a subset of genes whose differential expression was attributed to elevated pressure. In the pressure-shock case, this transcriptional response was evident despite the absence of a piezophilic growth response. In all, despite the piezophilic capacity and high-pressure origins of M. jannaschii, the core pressure response was remarkably limited and consisted of differential expression of genes encoding three hypothetical proteins and a gene involved in DNA recombination.

Methane production by methanogens following an aerobic washing procedure: simplifying methods for manipulation.

The recent discovery of methane in the martian atmosphere is arguably one of the most important discoveries in the field of astrobiology. One possible source of this methane could be a microorganism analogous to those on Earth in the domain Archaea known as methanogens. Methanogens are described as obligately anaerobic, and methods developed to work with methanogens typically include anaerobic media and buffers, gassing manifolds, and possibly anaerobic chambers. To determine if the time, effort, and supplies required to maintain anaerobic conditions are necessary to maintain viability, we compared anaerobically washed cells with cells that were washed in the presence of atmospheric oxygen. Anaerobic tubes were opened, and cultures were poured into plastic centrifuge tubes, centrifuged, and suspended in fresh buffer, all in the presence of atmospheric oxygen. Washed cells from both aerobic and anaerobic procedures were inoculated into methanogenic growth media under anaerobic conditions and incubated at temperatures conducive to growth for each methanogenic strain tested. Methane production was measured at time intervals using a gas chromatograph. In three strains, significant differences were not seen between aerobically and anaerobically washed cells. In one strain, there was significantly less methane production observed following aerobic washing at some time points; however, substantial methane production occurred following both procedures. Thus, it appears that aerobic manipulations for relatively short periods of time with at least a few species of methanogens may not lead to loss of viability. With the discovery of methane in the martian atmosphere, it is likely that there will be an increase in astrobiology-related methanogen research. The research reported here should simplify the methodology.