Electricity from cellulose
Microbes taken from a cow’s rumen are able to power a microbial fuel cell by digesting cellulose, which is widely available as a potential fuel.
By using bacteria and fungi from the stomachs of cows, researchers from the Ohio State University have created one of the first microbial fuel cells (MFCs) to generate electricity by digesting cellulose, the primary constituent of plants. The development is notable because although cellulose is widely available as a potential substrate for powering MFCs, it is remarkably hard to break down.
A team of students and faculty capitalized on the ability of cows and other ruminants to break down cellulose in their rumens, the first of several stomachs. The bacteria and fungi in rumen fluid are a key source of the cellulolytic enzymes that metabolize cellulose. In these experiments, the organisms, which included bacteria, fungi, and protozoa, were able to generate electricity without requiring the addition of other chemicals, known as exogenously added redox mediators, to generate electricity by transferring electrons from metabolic processes to the electrode. The need to replenish used-up redox mediators is a major limitation of many prototype MFCs.
The researchers have not yet identified any of the organisms in the microbial consortium that powered their MFC, but Hamid Rismani-Yazdi, one of the students involved in the project, says that maximum energy generation apparently involved cooperation among several species of bacteria and, possibly, fungi. When they inhibited the growth of many species of bacteria by adding penicillin and streptomycin, broad-spectrum antibacterials, the researchers found that electricity production was reduced but not eliminated. This suggests that either antibiotic-sensitive and -resistant bacterial species cooperate or that fungi play a role, says Ann Christy, associate professor of food, agricultural, and biological engineering, and a coauthor on a paper about the MFC presented at the American Chemical Society meeting held in Washington, D.C., in August.
The researchers hope to determine whether rumen fungi are electrochemically active and whether they produce soluble redox mediators. To date, Christy says that no researchers have shown that anaerobic fungi can power MFCs. The development could lead to a whole new class of microorganisms with unique abilities for use in the fuel cells, she adds.
