MOSS LANDING, California—Monterey Bay Aquarium Research Institute (MBARI)
microbiologists report in the 20 July 2001 issue of the journal Science on new
techniques that combine the identification of microorganisms with their
biogeochemical activity. In the study, the researchers used the new approach to
identify marine microbes that consume methane, an important greenhouse gas.

“The method is providing a new window into the microbial world. Now it’s possible to
determine both the identity and function of naturally occurring microbes, at the level of
single cells. We don’t even have to grow them in the laboratory to do it,” said Ed
DeLong, leader of the research group.

“Until recently no one knew which microbes were involved in the oxidation of methane
in anoxic marine sediments,” adds Victoria Orphan, first author of the Science paper.
“By combining molecular and stable isotope techniques, we found a way to link
specific microbes to this important ocean process.”

In collaboration with Christopher House of Pennsylvania State University and
researchers from Woods Hole Oceanographic Institution and the University of
California, Los Angeles, the MBARI group used a remotely operated vehicle to collect
marine sediments from deep sea methane seeps in the Eel River Basin off California.
Molecular probes were used to identify archaea and sulfate-reducing bacteria in the
sediments. These microorganisms, 0.5 to 2 micrometers in diameter, can live without
oxygen and have not been grown in culture. First the scientists applied RNA probes,
then they used secondary ion mass spectrometry to determine stable carbon isotope
ratios of the individual microbe cells and cell aggregates. This method distinguished
microbes that use methane as a carbon source from those using carbon derived from
photosynthesis or other organic carbon sources.

The researchers showed that the archaea and bacteria cells could be identified
individually within the cell aggregates. The two kinds of microbes form a partnership
to extract energy from methane in the absence of oxygen. The methane-oxidizing
archaea at the core of the aggregate transfer carbon compounds to their
sulfate-reducing bacterial partners in the outer layers of the aggregate. Since nearly
80 percent of the methane in marine sediments is removed by these
methane-consuming microbes, the discovery provides new insight into a critical
process. Orphan and her colleagues are excited by the implications of this research,
as these techniques can be used to simultaneously identify environmentally important
microorganisms and characterize their metabolic activities in nature.


Note to media: Images available upon request.

Contact: Gail Piper de Mesa


Monterey Bay Aquarium Research Institute

Related links

  • 20 July 2001: Methane-Consuming Archaea Revealed by Directly Coupled Isotopic and Phylogenetic Analysis, Science, [summary – can be viewed for free once registered. A subscription fee is required for full access.]

    “Microorganisms living in anoxic marine sediments consume more than 80% of the methane produced in the world’s oceans. In addition to single-species aggregates, consortia of metabolically interdependent bacteria and archaea are found in methane-rich sediments. “

  • 20 July 2001: Biogeochemistry: ‘Inconceivable’ Bugs Eat Methane on the Ocean Floor, Science, [summary – can be viewed for free once registered. A subscription fee is required for full access.]

    “Most of the methane that rises toward the surface of the ocean floor vanishes before it even reaches the water. A team of researchers has provided the clinching evidence for where all that methane goes: It is devoured by vast hordes of mud-dwelling microbes that belong to a previously unknown species of archaea. These methane-eating microbes–once thought to be impossible–now look to be profoundly important to the planet’s carbon cycle.”