Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - NOVAMOX (Novel niches for anaerobic methane oxidation and their biogeochemical sigificance)

Teaser

Motivated by a series of recent discoveries, NOVAMOX provides the first comprehensive biogeochemical and microbial ecological analysis of methane consumption in anoxic freshwater systems and oceanic oxygen minimum zones, environments where such processes to date were largely...

Summary

Motivated by a series of recent discoveries, NOVAMOX provides the first comprehensive biogeochemical and microbial ecological analysis of methane consumption in anoxic freshwater systems and oceanic oxygen minimum zones, environments where such processes to date were largely ignored. We hypothesize that anaerobic microbial methane oxidation pathways are important sinks in for methane in these environments, thereby affecting methane emissions and the cycling of nitrogen, iron, and sulfur, as the cycling of these elements is coupled either directly or indirectly to methane oxidation. With the development of new incubation and sensing techniques necessary to detect the processes in their environment, we will identify and quantify active pathways of anaerobic methane oxidation, identify the organisms that catalyse these transformations, analyse their environmental distribution, characterize kinetic controls of their growth and metabolic activity, and analyse the isotopic signatures they may leave behind. The project will generate robust estimates of the biogeochemical significance of anaerobic methane oxidation in these overlooked niches, and provide a quantitative mechanistic framework for analysis of the role of these processes in Earth’s biogeochemical evolution as well as for their implementation in forecasts of global change. The project will also provide fundamental new insights to the ecology of the highly specialized microorganisms involved in methane oxidation, for use in potential biotechnological applications.

Work performed

To date, we have pursued the project as planned with intensive studies in both oceanic oxygen minimum zones (OMZs; oceanic waters where oxygen is depleted and anaerobic processes prevail) and freshwater systems. We have studied methane cycling in the eastern tropical North Pacific and in the adjacent Golfo Dulce, Costa Rica, where waters with OMZ-like conditions are easily accessed. Our studies provide the first evidence for active methane consumption by anaerobic oxidation in the OMZ waters. The eastern tropical North Pacific holds the largest accumulation of methane in the open ocean, and our results imply that this methane pool is highly dynamic, and that consumption by anaerobic methane-oxidizing microbes is the main methane sink, substantially attenuating the transport of methane to surface water and eventually to the atmosphere. We have identified several different types of microbes that likely contribute to methane consumption. This work required the development of highly sensitive methods to measure the microbial processes in the water column. While our measurements were so far conducted on samples recovered to the laboratory, we have also worked on development of a system for incubation in situ, i.e. directly within the water column, in order to avoid potential artefacts resulting from sample recovery. We have performed the first field tests and look forward to obtaining the first rate measurements.

In freshwater systems, we have determined rates of anaerobic methane oxidation at a range of different locations and explored how process rates depend on environmental parameters. We find that methane is oxidized anaerobically in diverse habitats and with an array of different oxidants including nitrate, nitrite, ferric iron, and sulfate. We also find that anaerobic methane oxidation in some settings efficiently traps methane and prevents its emission to the atmosphere. We have identified a group of microbes that appears to be of particular importance for oxidizing methane with iron and/or sulfate as electron acceptor, and we are exploring the ecophysiology of these organisms with both biogeochemical and molecular biological techniques.

Final results

Our findings in the oceanic oxygen minimum zones essentially launch methane cycling in anoxic waters as a new important field of research in marine biogeochemistry. The results not only demonstrate that methane is actively consumed, but also provide strong indications of a large and unknown source of methane in OMZs. We will pursue this further until the end of the project, and are currently expanding our investigations to other oxygen depleted waters in order to establish a general understanding of anaerobic methane cycling in anoxic marine waters with identification of the key microorganisms involved.

Our results from freshwater systems demonstrate a wide distribution of anaerobic methane oxidation, which can be coupled to a diverse array of electron acceptors. The determination of the kinetics of these processes allows us to construct mathematical models to estimate the extent to which they attenuate methane fluxes, and how this function may vary in response to environmental change. We will also identify the organisms that carry out the processes, which may reveal candidates of biotechnological interest.