Greenhouse gas paradox

Global warming is a contentious issue, with different groups voicing opposing opinions on if, how and at what rate the warming is occurring. The general consensus is that with increased industrialization, greenhouse gas emissions have also increased, resulting in the formation of a so-called ‘greenhouse effect’. The origin of greenhouse gases is therefore of great interest to the scientific community.

Large sections of the worlds oxygenated ocean waters are supersaturated with methane, even though the only ‘significant’ biological source of methane are a group of marine microbes that inhabit deoxygenated waters. This unidentified source of methane constitutes up to 4% of the global methane budget¹.

A group of scientists in the USA¹ has published data suggesting a new source of ocean methane from an unsuspecting source, the marine archaeon Nitrosopumilus maritimus. It has been previously suggested in response to phosphate starvation that ocean microbes breakdown methylphosphonic acid resulting in the release of methane as a by-product. Until now, the source of methylphosphonic acid has remained undetected and its biosynthesis considered a physical impossibility when considering known and defined biochemical pathways within marine ecosystems.

Using a combination of nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography–mass spectrometry (LC–MS) the group demonstrated that the marine archaeon Nitrosopumilus maritimus encodes a metabolomic pathway for methylphosphonate biosynthesis and it produces methylphosphonate esters that are contained within the cell of the microbe. This approach identified a source of methylphosphonic acid precursor. Furthermore, metagenomic data indicated that methylphosphonate biosynthesis is relatively common in marine microbes, providing a plausible explanation for the methane paradox.

1. William W. Metcalf et al, Science, 1104–1107, DOI:10.1126/science.1219875, (2012)

This story originally appeared in The Column. Click here to view that issue.