Novel microbial communities of the Haakon Mosby mud volcano and their role as a methane sink

Mud volcanism is an important natural source of the greenhouse gas methane to the hydrosphere and atmosphere1, 2. Recent investigations show that the number of active submarine mud volcanoes might be much higher than anticipated (for example, see refs 35), and that gas emitted from deep-sea seeps might reach the upper mixed ocean6, 7, 8. Unfortunately, global methane emission from active submarine mud volcanoes cannot be quantified because their number and gas release are unknown9. It is also unclear how efficiently methane-oxidizing microorganisms remove methane. Here we investigate the methane-emitting Haakon Mosby Mud Volcano (HMMV, Barents Sea, 72° N, 14° 44' E; 1,250 m water depth) to provide quantitative estimates of the in situ composition, distribution and activity of methanotrophs in relation to gas emission. The HMMV hosts three key communities: aerobic methanotrophic bacteria (Methylococcales), anaerobic methanotrophic archaea (ANME-2) thriving below siboglinid tubeworms, and a previously undescribed clade of archaea (ANME-3) associated with bacterial mats. We found that the upward flow of sulphate- and oxygen-free mud volcano fluids restricts the availability of these electron acceptors for methane oxidation, and hence the habitat range of methanotrophs. This mechanism limits the capacity of the microbial methane filter at active marine mud volcanoes to <40% of the total flu

A novel hydrogen oxidizer amidst the sulfur-oxidizing Thiomicrospira lineage

Thiomicrospira species are ubiquitously found in various marine environments and appear particularly common in hydrothermal vent systems. Members of this lineage are commonly classified as sulfur-oxidizing chemolithoautotrophs. Although sequencing of Thiomicrospira crunogena's genome has revealed genes that encode enzymes for hydrogen uptake activity and for hydrogenase maturation and assembly, hydrogen uptake ability has so far not been reported for any Thiomicrospira species. We isolated a Thiomicrospira species (SP-41) from a deep sea hydrothermal vent and demonstrated that it can oxidize hydrogen. We show in vivo hydrogen consumption, hydrogen uptake activity in partially purified protein extracts and transcript abundance of hydrogenases during different growth stages. The ability of this strain to oxidize hydrogen opens up new perspectives with respect to the physiology of Thiomicrospira species that have been detected in hydrothermal vents and that have so far been exclusively associated with sulfur oxidation

Potential influence of sulphur bacteria on Palaeoproterozoic phosphogenesis

All known forms of life require phosphorus, and biological processes strongly influence the global phosphorus cycle. Although the record of life on Earth extends back to 3.8 billion years ago and the advent of biological phosphate processing can be tracked to at least 3.5 billion years ago,the earliest known P-rich deposits appeared only 2 billion years ago. The onset of P deposition has been attributed to the rise of atmospheric oxygen 2.4–2.3 billion years ago and the related profound biogeochemical shifts which increased the riverine input of phosphate to the ocean and boosted biological productivity and phosphogenesis. However, the P-rich deposits post-date the rise of oxygen by about 300 million years. Here we use microfabric, trace element and carbon isotope analyses to assess the environmental setting and redox conditions of the 2-billion-year-old P-rich deposits of the vent- or seep-influenced Zaonega Formation, northwest Russia. We identify phosphatized microorganism fossils that resemble modern methanotrophic archaea and sulphur-oxidizing bacteria, analogous to organisms found in modern seep settings and upwelling zones with a sharp redoxcline. We therefore propose that the P-rich deposits in the Zaonega Formation were formed by phosphogenesis mediated by sulphur bacteria, similar to modern site, and by the precipitation of calcium phosphate minerals on microbial templates during early diagenesis