Cable Bacteria Are Living Batteries

Summary

Under a cloudless August sky, I sailed upon an InterCity train from København station to Aarhus, an 8th-century Viking settlement that is now the second largest city in Denmark. After disembarking, I trekked toward the local university to a door marked INSTITUT FOR BIOLOGI. Upon entering, I was greeted by Ian Marshall, a lanky Australian professor with graying hair, who ushered me into his first floor laboratory.Dimly lit, the room was thick with the scent of wet earth. Large plastic buckets lined the walls, each filled with mud dredged from a nearby lake. Water-filled tanks sat on benches, bristling with a tangle of electrical probes and wires. Glass vials packed with dark sediment nestled in bubbling incubators. The room looked less like a biology lab and more like a cross between a hardware shop and a swamp; an engineered environment designed to coax electricity from mud.Marshall beckoned me to a microscope. Peering through the eyepiece, I saw fine, translucent filaments swaying gently against a dark backdrop. “What is this?” I asked. “It looks like hair.” Marshall chuckled. “That’s them — the cable bacteria,” he said. “If you watch closely, you’ll see them twitching.” I stared harder. The filaments shifted.The Institut for Biologi at Aarhus University, with bikes parked in front. Photo by the author.A quiet street in Aarhus. Photo by the author.Although Aarhus University is not widely known outside Denmark (it wasn’t founded until the 1920s), it was here where scientists first identified the properties of the cable bacteria that I watched through Marshall’s microscope — a microbe that has revised much of what biologists know about bioenergetics.A team of Aarhus scientists first discovered cable bacteria in a nearby lake in 2012. These microbes stack together, thousands of cells end to end, to form centimeters-long chains. One tip of this microbial chain oxidizes sulfide in the mud, stripping it of electrons. Once freed, those electrons then race up the chain tow...