Nature's little power plants

Natural History, Oct, 2005 by Rebecca E. Kessler

As if gobbling up some of humankind's worst pollutants--solvents, dry-cleaning chemicals, pesticides, and the like--weren't helpful enough, a certain microorganism has revealed yet another useful talent.

Harold D. May, a microbiologist at the Medical University of South Carolina in Charleston, and his colleagues were exploring the pollution-eating abilities of Desulfitobacterium, a genus of freshwater anaerobic bacteria, when he discovered that it also makes electricity.

What surprised May was not that bacteria can generate electricity; that has been known since 1912. But Desulfitobacterium is quite distinct from other electricity-generating bacteria. Until May's discovery, microbiologists thought only Gram-negative bacteria, with two cell membranes (an inner and an outer), could create a voltage, or electric potential difference, between the two membranes (proteins embedded in the outer membrane then may be able to conduct the electric current generated by the potential difference). Desulfitobacterium, however, is Gram-positive, with just one cell membrane that may or may not carry embedded proteins. So the bacterium must make electricity in a distinct way; the mechanism remains a mystery that May is still exploring.

Desulfitobacterium is also the only known electricity-producing microorganism that can form spores--inactive life stages that can withstand extreme drying, heat, and radiation. May imagines that a fuel cell powered by Desulfitobacterium could remain dormant for long periods before springing to life. Perhaps one could be made suitable for long-distance space travel. (Presented at the 105th General Meeting of the American Society for Microbiology, June 5-9, 2005)