A company called Living Power System has developed a process wherein electricity — at this stage, enough to run relatively low-power devices like LED lights — is generated from soil. In s sort of a living fuel cell, microbes growing across an electrode planted in the earth generate an electron flow as they metabolize nutrients in the soil.
http://www.news.com/8301-10784_3-9809164-7.html

It’s another example of a biotech energy generation mechanism besides the more familiar microbes-digesting-switchgrass to generate ethanol.