Methane bacteria possess pressure valve

Microbiologists from the University of Nijmegen have discovered that a methane-forming archaeabacterium sometimes deliberately allows hydrogen ions to leak out of its cell. At high hydrogen concentrations in particular, the cell membrane works as a sort of pressure valve. The waste of energy seems to be of vital importance for the microorganism.

The researchers examined how a bacterium adapts to changing circumstances. The study focussed on the behaviour of the relatively simple methane producing microorganism Methanothermobacter thermoautotrophicus. In order to grow, this so-called archaeabacterium obtains hydrogen from the environment. However, the quantity of hydrogen, that is the food available, can vary considerably. The methane bacterium seems to use this to its advantage.

At high hydrogen concentrations, thus an excess of food, the bacterium grows as quickly as possible. In so doing the organism loses energy but at this point in time plenty of energy is available anyway. Furthermore, this wastage is a bonus as it results in the difference between the hydrogen ion concentrations inside and outside of the cell becoming smaller. Under these circumstances this is desirable, as otherwise a range of processes in the cell might cease to continue.

The observations confirm the prediction made in a mathematical model. That model, constructed by the Nijmegen research group, not only predicted that the methane bacteria would waste energy, but also how that would occur. At high hydrogen concentrations the microorganism would allow hydrogen ions to leak through the cell membrane. In this case the cell membrane would act as a sort of excess pressure valve.

The model summarises about 2000 different reactions in a small number of biochemical and thermodynamic equations. The researchers have now subjected the model and the assumptions on which it is based to extensive experimental testing. As had been assumed, the important reactions in the methane-forming process proceeded without energy loss.

Despite its relative simplicity, the model seems to accurately predict the behaviour of the microorganism. This implies that apparently complicated processes can in fact be determined by simple thermodynamic principles.

The researchers expect that this is not only the case for methane-forming bacteria but might also apply to other forms of life. This means that the research is not only interesting for microbiologists, but also for chemists, physicians, botanists and zoologists.

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