Microbiologists and geochemists have shown that marine methane oxidation coupled to sulfate respiration can be performed by a single microorganism, a member of the ancient kingdom of the Archaea, and doesn't need to be carried out in collaboration with a bacterium, as previously thought.
Vast amounts of methane are stored under the ocean floor. Anaerobic oxidation of methane coupled to sulfate respiration (AOM) prevents the release of this potent greenhouse gas into the atmosphere. Although the process was discovered 35 years ago it has remained a mystery how microorganisms perform this reaction. A decade ago, it was discovered that two different microorganisms are often associated with AOM. It was proposed that these two microorganisms perform different parts of the AOM reaction. One, an archaeon, was supposed to oxidize methane and the other, a bacterium, was supposed to respire sulfate. This implied the existence of an intermediate compound to be shuttled from the methane oxidizer to the sulfate respirer.
Now, a team has shown that the archaeon not only oxidizes methane but can also respire sulfate and does not necessarily need the bacterial partner. It appears that the archaeon does not employ the common enzyme toolbox that other known sulfate-respiring microorganisms use, but relies on a different, unknown pathway.
In this model, methane oxidation and sulfate respiration to elemental sulfur (or all the way to sulfide) is performed by the methanotrophic archaea (ANME). The associated bacteria (DSS) are disproportionators (sulfur fermentors), which take up produced elemental sulfur in the form of disulfide and turn it into sulfate and sulfide. Dark circles represent iron- and phosphorus-rich precipitates found in the bacteria. Credit: Jana Milucka, MPI f. Marine Microbiology
The basis for this shift in thinking is the observation that elemental sulfur is formed and accumulates in the methane-oxidizing archaeon. “Using chromatographic and state-of-the-art spectroscopic techniques we found surprisingly high concentrations of elemental sulfur in our cultures,” says Professor Marcel Kuypers from the Max Planck Institute for Marine Microbiolog, “The single-cell techniques showed that the sulfur content in the methane-degrading archaeon was much higher than in the bacterium. Our experiments show that this sulfur is formed during sulfate respiration.”
What does the bacterium do if the archaeon does both sulfate respiration and methane oxidation? “The bacteria actually make a living off of the elemental sulfur produced by the archaea,” explains Jana Milucka, first author of the study. “The bacteria grow by splitting the elemental sulfur into sulfate and hydrogen sulfide. This is a form of fermentation, like the process that produces alcohol.”
The enrichment of the microorganisms responsible for marine AOM, archaea in red and bacteria in green from the Isis Mud Volcano in the Mediterranean Sea has taken 8 years of continuous incubation. Without these cultures it would not have been possible to trace down the complex sulfur cycling involved in AOM. Credit: Jana Milucka, MPI for Marine Microbiology
“Until now we have always had trouble explaining the occurrence of elemental sulfur in oxygen-free sediments,”, notes co-author Tim Ferdelman, scientist at the MPI Bremen. ”Our discoveries not only provide a mechanism for marine methane oxidation but also cast a new light on the carbon and sulfur cycling in marine, methane-rich sediments.”
Citation: Jana Milucka, Timothy G. Ferdelman, Lubos Polerecky, Daniela Franzke, Gunter Wegener, Markus Schmid, Ingo Lieberwirth, Michael Wagner, Friedrich Widdel, Marcel M. M. Kuypers, 'Zerovalent sulfur is a key intermediate in marine methane oxidation', Nature, 2012. 8 November, 2012. Doi: 10.1038/nature11656
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- How A Former Naturopath Can Help Unravel The Trickery of Alternative Medicine
- Can A New Rule Trigger A Second EU Referendum? Petition Signatures Over 9.7% Of Total Votes Cast
- Better Brains With Beer
- Beneficial Bacteria May Protect Breasts From Cancer
- Some Celiac Disease May Be Due To Viruses
- Finding All-Hadronic Top - Again
- Cross Talk Between Hormone Receptors Has Unexpected Effects
- "However you might be interested to know, we have an interesting system in the Scottish Government..."
- "Right sorry that's probably based on my earlier version of the article and facebook posts. I got..."
- "There's the issue of the population. Even the Puerto Ricans that I work with have a low opinion..."
- "Good for you! Glad to see you've seen the light and are even going so far aa to pursue a degree..."
- "In today's world that is a problem. When the country founded by your ancestors is no longer..."
- Chemistry Can Help Roast the Perfect Coffee Bean
- What Happens To A Soccer Player’s Brain After Missing A Penalty Kick
- It’s Back to Shots for Flu Prevention
- ACSH Applauds Media Awareness of the Fentanyl Crisis
- Counting Bites Examined, to Help Decrease Food Intake
- The Safe And Unsafe Nutty Treats For Your Pup