"The geochemistry is interesting in itself, but there are also potentially useful implications which may derive form this work," said study leader Dr James Byrne from the University of Tubingen, Germany. The flow of electrons is critical to the existence of all life and the fact that magnetite can be considered to be redox active opens up the possibility of bacteria being able to exist or survive in environments where other redox active compounds are in short supply in comparison to magnetite.
In our study we only looked at iron metabolising bacteria, but we speculate that it might be possible for other non-iron metabolising organisms to use magnetite as a battery as well - or if they can be made to use it, through genetic engineering. Researchers from Tubingen, the University of Manchester, and Pacific Northwest National Laboratory, US, incubated the soil and water dwelling purple bacteria Rhodopseudomona palustris with magnetite and controlled the amount of light the cultures were exposed to.
Using magnetic, chemical and mineralogical analytical methods, the team showed that in light conditions which replicated the day-time, phototrophic iron-oxidising bacteria removed electrons from the magnetite, thereby discharging it. During the night-time conditions, the ironreducing bacteria took over and were able to dump electrons back onto the magnetite and recharge it for the following cycle. This oxidation/reduction mechanism was repeated over several cycles, meaning that the battery was used over repeated day-night cycles.
Whilst this work has been on iron-metabolising bacteria, it is thought that in the environment the potential for magnetite to act as a battery could extend to many other types of bacteria which do normally not require iron to grow, e.g. fermenters. The study was published in the journal Science.