It was already known that microorganisms other than ANME develop nanowires, but it was not yet known whether ANME did too. Welte: 'We have been searching for these answers for so long, and now we can see that these microorganisms feed electricity back to an electrode via their self-made nanowires. We already strongly suspected this would be the case, and have now been able to visualise it beautifully under a special microscope.'
Welte's research revealed that ANME love growing on an electrode through which a small voltage is passing. In fact, they enjoy it so much that they grow much faster there than they do in the wild. 'ANME divide once a month when they're out in ditches and trenches, but on the electrodes in our lab, they divide once every five days. So that works very well.'
Hydrogen
In Welte's lab, the microorganisms grow in a small vessel containing water. They are fed methane and attach themselves to an electrode in the water, where they multiply. They also send electrons to the electrode, which means they generate a small amount of current. This current could be used, for example, to produce hydrogen, although, according to Welte, this is still a long way off. 'In theory, the microorganisms can generate electricity from methane using a small amount of voltage, much more efficiently than, for example, a electrolyzer can. That could be a practical application in about twenty years' time, but for now, we are mainly looking at how these ANME work at a fundamental level.'
The researchers also succeeded in culturing the ANME in such a way that 95 per cent of the microbial community consisted of these ANME. This had never been achieved before. 'If you have such a pure culture, you can study these microorganisms much more effectively than when everything is growing together. We achieved this through collaboration with various partners, including researchers from Yale.'
Future
Welte points out that this technique could become highly relevant in the future. 'As natural resources run out, we will have to find new, energy-efficient ways to generate electricity. This could be achieved by using microorganisms. But at present, the technique is still far too expensive and complex. Hopefully, it can be made more efficient in the future. With this research, we've taken another small step in that direction.'
Image created by Cornelia Welte, (c) Cong Shen and Nikhil Malvanker.
