Published online 15 September 2010 | Nature | doi:10.1038/news.2010.469
Corrected online: 21 September 2010

News

Microbe carries minimalism to extremes

Heat-loving organisms survive on surprisingly meagre rations.

black smoker vent'Extremophile' microbes in deep ocean vents have been found to live on energy produced by formate oxidation.P. Rona/ OAR/National Undersea Research Program (NURP); NOAA

Whether the world ends in fire or ice, drought or nuclear war, the last organisms standing will be the extremophiles — microbes that thrive in radioactive ponds, glaciers, acidic conditions and boiling sea water.

Researchers report in this week's issue of Nature that Thermococcus onnurineus, a single-celled organism known as an archaeon living in deep-sea vents, has another enviable ability. It is the first microbe found to survive on the meagre energy provided by a very simple respiratory pathway: the conversion of formate (HCOO) and water into hydrogen and bicarbonate1.

"They've described a single organism that can make a living right at the thermodynamic edge," says Edward DeLong, a microbiologist at the Massachusetts Institute of Technology in Cambridge, who was not involved in the study. "It really does help us push the envelope a little further on how few substrates microbes can live on."

To grow and metabolize, organisms need energy in the form of ATP. They synthesize this by converting compounds from the environment into other molecules by way of reduction–oxidation, or redox, reactions. These shuffle electrons between atoms or molecules, generating minute amounts of energy. About 70 kilojoules (kJ) is required to make each mole of ATP.

During respiration, animals derive roughly 2,000 kJ per mole of glucose from a redox reaction that converts glucose and oxygen into carbon dioxide and water. Plants, meanwhile, undergo photosynthesis, deriving energy from sunlight-fuelled redox reactions that convert carbon dioxide and water into oxygen and organic compounds. Bacteria and archaea enjoy greater flexibility and, if there is no oxygen available, can derive ATP from redox reactions involving other compounds, such as sulphur or methane.

The use of formate is a different story, particularly when paired with hydrogen ions, or protons, rather than a strong electron acceptor like oxygen. In this case, the reaction yields negligible energy at room temperature.

In 2008, researchers reported that bacteria can derive energy from the conversion of formate and water into hydrogen and bicarbonate if they are cultured alongside other microbes that facilitate the reaction by consuming the hydrogen waste product2. The scientists proposed that in extremely limited, anoxic environments, microbes benefit from such partnerships.

Going it alone

However, the team responsible for the current work, led by Sung Gyun Kang at the Korea Ocean Research & Development Institute in Ansan, show that T. onnurineus, found 1,650 metres below sea level, in hydrothermal vents near Papua New Guinea, can grow on formate without the help of bacteria when incubated at 80 ºC. Temperatures in hydrothermal vents inhabited by Thermococcus can reach 90 ºC — hot enough to quickly burn human skin.

The standard conditions assuming room temperature in thermodynamic calculations don't represent the natural environment for this biological system, explains Kang. According to his calculations, at 80 ºC the oxidation of formate, and acceptance of its electrons by protons, yields 8–20 kJ per mole.

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"That's still very little energy, but apparently enough to synthesize ATP," says Costantino Vetriani at Rutgers University in New Brunswick, New Jersey. "And that's pretty remarkable because formate is a very simple molecule, and a proton is the simplest of all electron acceptors," he says. "It's a very, very simple pathway for energy synthesis."

The reaction by T. onnurineus is dependent on genes that encode proteins able to break apart formate and transport it along with protons and electrons. Other Thermococcus species have similar genes, and are likewise capable of such a bare-bones existence.

Bacteria and archaea probably inhabited Earth long before oxygen became a major component of the atmosphere. "If you accept that life arose in anaerobic conditions," says Vetriani, "it could imply that this capability was a very early system." 

Corrected:

An earlier version of this story incorrectly stated that animals derive roughly 2,000 kJ per molecule of glucose.
  • References

    1. Kim, Y. J. et al. Nature, 467, 352-355 (2010). | Article
    2. Dolfing, J. et al. Appl. Environ. Microbiol. 74, 6126-6131 (2008). | Article | PubMed | ChemPort |

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  • #60920

    Despite the fact that I agree that microbes are self-aware, I think that using a term like cognition is stretching the boundaries.

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