Our paper applies a novel molecular and isotopic-based approach to gain new insight into the anaerobic oxidation of methane, a globally significant process consuming up to 80% of methane produced in the world’s oceans. Although this microbially-driven process has been recognized for decades, the responsible microorganisms were unknown, with no cultured representatives shown to be capable of net oxidation of methane under anaerobic conditions. Recently, the application of culture-independent methods to this problem has led to a number of important discoveries, including the identification of uncultured groups of putative methane-oxidizing microorganisms recovered directly from the environment. These advancements have sparked renewed interest in this process by microbiologists and geologists alike. In addition to significantly contributing to our understanding of the anaerobic oxidation of methane, this paper also introduces a new powerful technique that enables the direct linking of microorganisms from nature to certain biogeochemical cycles and has been cited by others developing similar methodologies.

Yes, it describes a new discovery as well as a new methodology that may be applicable to studies in microbial ecology/ geomicrobiology. In this work, we developed a novel approach for assessing the function of specific, phylogenetically identified microorganisms recovered directly from the environment. This was accomplished by combining two distinct methods- whole cell fluorescent in situ hybridization and secondary ion mass spectrometry (FISH-SIMS). The first is a culture-independent technique used to visually identify environmental microorganisms by staining their ribosomal RNA, and the second is geochemical technique capable of measuring stable carbon isotope values in microsamples. The two techniques together allowed us to identify anaerobic methane-consuming microorganisms in nature by directly determining the stable carbon isotope composition of their biomass.

This work was an ideal collaboration. As a Ph.D. student working with Ed DeLong at MBARI, Victoria was investigating the diversity of microorganisms associated with anaerobic methane oxidation in methane seep environments, while Chris had recently finished a project using the SIMS instrument to obtain geochemical information from microfossils. We met through another collaborator, Kai-Uwe Hinrichs, of the Woods Hole Oceanographic Institution, who was characterizing lipid biomarkers related to methane oxidizing microorganisms from methane seep sediments. Together, our team was able to identify microorganisms from the environment and test whether or not they had grown on methane.

Victoria J. Orphan,
National Research Council Associate,
NASA Ames Research Center,
Moffett Field, CA 94035

Christopher H. House,
Assistant Professor,
Department of Geosciences,
Pennsylvania State University,
University Park, PA 16802