A study undertaken by scientists from Oregon State University (OSU) has revealed that ocean’s most abundant organism, SAR11 has the ability to generate methane as a by-product. Methane is produced in the oceans with low levels of oxygen as a result of ‘anaerobic biogenesis’. However, it was a mystery as to how surface waters of Pacific and Atlantic oceans which are abundant with oxygen, possess so large amount of methane. This phenomenon is termed as ‘marine methane paradox’.
The research showed that certain strains of SAR11 (smallest free-living cell), when starved for phosphorous transformed into a compound known as methylphosphonic acid. The organism then produces enzymes that can break this compound, thus separating phosphorous and methane.
Earlier research had shown that adding methylphosphonic acid or MPn to seawater produces methane but no one knew how. A research was then led by David Karl of the University of Hawaii and OSU's Angelique White in which they found an organism called Trichodesmium that could break down MPn by separating phosphorous. However, Trichodesmium are rare in the marine environment and thus unlikely to be the only source of vast methane deposits in the surface waters.
The duo then approached Steve Giovannoni, a professor of microbiology at OSU, who discovered and identified SAR11 in 1990. In a series of experiments, the team tested the capacity of different SAR11 strains to consume MPn and cleave off methane. In the ensuing tests, it was revealed that some did produce a methane by-product while some did not. They finally arrived at a conclusion that phosphate starved bacterioplankton have the capability of producing methane in oxygen rich waters.