Vinegar microbes: "cell turbine" as an energy source

Initial type of cellular respiration detected in acidic bacteria

Fno complex of anaerobic bacterium Acetobacterium woodii. © Volker Müller
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Acetic acid-forming bacteria are, according to many researchers, among the first living beings on earth. They draw their energy from the conversion of carbon dioxide, which they use to reduce hydrogen to activated acetic acid. But where does this biochemically well-researched process release energy? Frankfurt bioscientists have now succeeded in solving this puzzle.

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In the membrane of Acetobacterium woodii they found an enzyme that transports sodium ions out of the cell against an energy gradient. The sodium ions pass back into the cell via a "turbine" in the cell membrane - ATP synthase. Passage releases energy in the form of ATP.

"The discovery of this new type of electron-transport driven membrane pump, the ferredoxin: NAD oxidoreductase, could not only be an archetype for today's electron transport pumps, as we find them in mitochondria, " reports Professor Volker Müller from the Goethe University Frankfurt am Main his doctoral student Eva Biegel in the current issue of the "Proceedings of the National Academy of Sciences" (PNAS).

Pump explains the lifestyle of many microbes

"This pump also explains the lifestyle of many other microorganisms, " says Müller. It is therefore not surprising that the genes coding for it are found in the genomes of over 100 different prokaryotes. Many of them live in the strict absence of oxygen, and it is likely that ferredoxin: NAD oxidoreductase, or Fno for short, is also used for energy conservation. display

Fno also occurs in bacteria that live in the air. Their cellular function there is still misunderstood. "We assume that the turbine is going in the other direction there, using the electrochemical energy across the membrane to pump electrons against the energy gradient, " Biegel suspects. This is the case, for example, with nitrogen fixation or the sensing of oxidative stress, both functions also require Fno.

Researchers reveal biochemical process

According to the scientists, the biochemical process looks like this: hydrogen is oxidized by the enzyme hydrogenase and the electrons are transferred to the protein ferredoxin. Both contain iron and sulfur, elements that were abundant in primordial soup. The reduced ferredoxin is the fuel for a membrane-bound turbine, the ferredoxin: NAD oxidoreductase (Fno). This enzyme transmits, again via iron-sulfur centers, the electrons to the acceptor NAD +, and from there the electrons flow into the cell interior for CO2 fixation.

According to the researchers, the Fno turbine uses the energy of the "down-hill", ie electrons flowing with energy, to "climb" sodium ions out of the cell interior to pump. The sodium ions then flow downhill through another turbine, the ATP synthase, which uses the released energy to generate ATP.

(idw - Goethe-University Frankfurt am Main, 06.10.2010 - DLO)