Kinetic fractionation of stable isotopes in speleothems : laboratory and in situ experiments

In recent years, stalagmites have become an important archive for paleoclimate. Several studies about stable isotope records in stalagmites show a simultaneous enrichment of d18O and d13C along individual growth layers, which is associated with kinetic isotope fractionation. However, to deduce paleoclimatic information from calcite which is precipitated under these non-equilibrium-conditions,it is important to improve the understanding of kinetic isotope fractionation in dependence of local conditions like temperature and drip rate. Within this research work, laboratory experiments with synthetic carbonates were carried out under controlled conditions. The d18O and d13C evolution of the precipitated calcite were studied for different experiment parameters such as the initial composition of the solution, temperature and drip rate. In addition, in situ experiments were carried out in two cave systems in Sauerland (Bunkerhöhle and B7-Höhle). The modern calcite collected at three drip sites was compared with the calcite obtained from the laboratory experiments. All experiments show a distinct isotopic enrichment along the precipitated calcite. Lower drip rates, higher temperatures and higher initial supersaturation with respect to calcite result in a greater total isotopic enrichment and in a lower slope of the linear correlation d18O(d13C). The latter indicates a larger oxygen isotope buffering from the water reservoir. From a comparison with theoretical models it can be concluded that the conversion reactions between the bicarbonate and the carbon dioxid and the exchange reactions between the oxygen isotopes in the bicarbonate and the water reservoir occur faster than predicted from present publications, particularly in case of higher temperatures (23°C). Thus, for higher temperatures other effects might play a role not yet considered in theoretical models

ROS-driven cellular methane formation: Potential implications for health sciences

Abstract Recently it has been proposed that methane might be produced by all living organisms via a mechanism driven by reactive oxygen species that arise through the metabolic activity of cells. Here, we summarise details of this novel reaction pathway and discuss its potential significance for clinical and health sciences. In particular, we highlight the role of oxidative stress in cellular methane formation. As several recent studies also demonstrated the anti-inflammatory potential for exogenous methane-based approaches in mammalians, this article addresses the intriguing question if ROS-driven methane formation has a general physiological role and associated diagnostic potential

Genomics and metagenomics of trimethylamine-utilizing Archaea in the human gut microbiome

International audienceThe biological significance of Archaea in the human gut microbiota is largely unclear. We recently reported genomic and biochemical analyses of the Methanomassiliicoccales, a novel order of methanogenic Archaea dwelling in soil and the animal digestive tract. We now show that these Methanomassiliicoccales are present in published microbiome data sets from eight countries. They are represented by five Operational Taxonomic Units present in at least four cohorts and phylogenetically distributed into two clades. Genes for utilizing trimethylamine (TMA), a bacterial precursor to an atherosclerogenic human metabolite, were present in four of the six novel Methanomassiliicoccales genomes assembled from ELDERMET metagenomes. In addition to increased microbiota TMA production capacity in long-term residential care subjects, abundance of TMA-utilizing Methanomassiliicoccales correlated positively with bacterial gene count for TMA production and negatively with fecal TMA concentrations. The two large Methanomassiliicoccales clades have opposite correlations with host health status in the ELDERMET cohort and putative distinct genomic signatures for gut adaptation