A spark from the compost heap.

It is time to take a shine to Geobacter sulfurreducens. This little microbe, when grown in a microbial fuel cell containing graphite rods, can produce a stable, low-level electrical current, according to a team from the University of Massachusetts, reporting in the Journal of Applied and Environmental Microbiology. The good thing is that they do not need a toxic mediator to keep them going.
"These findings greatly expand the potential for using microorganisms to convert organic matter to electricity," they say.