Variation of carbon isotope fractionation in hydrogenotrophic methanogenic microbial cultures and environmental samples at different energy status

Methane is a major product of anaerobic degradation of organic matter and an important greenhouse gas. Its stable carbon isotope composition can be used to reveal active methanogenic pathways, if associated isotope fractionation factors are known. To clarify the causes that lead to the wide variation of fractionation factors of methanogenesis from H2 plus CO2 ( ), pure cultures and various cocultures were grown under different thermodynamic conditions. In syntrophic and obligate syntrophic cocultures thriving on different carbohydrate substrates, fermentative bacteria were coupled to three different species of hydrogenotrophic methanogens of the families Methanobacteriaceae and Methanomicrobiaceae. We found that C-isotope fractionation was correlated to the Gibbs free energy change (¿G) of CH4 formation from H2 plus CO2 and that the relation can be described by a semi-Gauss curve. The derived relationship was used to quantify the average ¿G that is available to hydrogenotrophic methanogenic archaea in their habitat, thus avoiding the problems encountered with measurement of low H2 concentrations on a microscale. Boreal peat, rice field soil, and rumen fluid, which represent major sources of atmospheric CH4, exhibited increasingly smaller , indicating that thermodynamic conditions for hydrogenotrophic methanogens became increasingly more favourable. Vice versa, we hypothesize that environments with similar energetic conditions will also exhibit similar isotope fractionation. Our results, thus, provide a mechanistic constraint for modelling the 13C flux from microbial sources of atmospheric CH4

Environmental vulnerability of the global ocean plankton community interactome

Marine plankton form complex communities of interacting organisms at the base of the food web, which sustain oceanic biogeochemical cycles, and help regulate climate. Though global surveys are starting to reveal ecological drivers underlying planktonic community structure, and predicted climate change responses, it is unclear how community-scale species interactions will be affected by climate change. Here we leveraged Tara Oceans sampling to infer a global ocean cross-domain plankton co-occurrence network – the community interactome – and used niche modeling to assess its vulnerabilities to environmental change. Globally, this revealed a plankton interactome self-organized latitudinally into marine biomes (Trades, Westerlies, Polar), and more connected poleward. Integrated niche modeling revealed biome-specific community interactome responses to environmental change, and forecasted most affected lineages for each community. These results provide baseline approaches to assess community structure and organismal interactions under climate scenarios, while identifying plausible plankton bioindicators for ocean monitoring of climate change

The fostering of cross-disciplinary science as a result of the IPY: “connectivity” created by the Canada Three Oceans project

The fourth International Polar Year (IPY), which ended in March 2009, represented a ca. 50% increase in the funding of polar science, a major expansion of the observing effort across polar and subpolar seas, the deployment of a wide range of new and complex observing techniques and a gratifying new degree of international collaboration in their use. As a result, the IPY has revolutionized our polar data sets to provide our first real glimpse of the ocean–atmosphere–cryosphere operating as a complete system. Here we focus on one particular aspect of the emerging results—the “connectivities” that may develop between individual research projects over time, developing the complexity of our understanding in real if unexpected ways as new findings emerge, ramify and mesh within projects or between them. For simplicity, we illustrate this valuable but unpredictable process by using one particular Arctic–sub-Arctic project—Canada Three Oceans—as our initial reference point and attempting to trace out a small subset of its inter-connections across space, time, projects and disciplines