Electron Gradients in Biofilms
Microbes play a key role in determining the chemical form of metal and radioactive contaminants in the environment. They shuttle electrons back and forth with metal ions, often over long distances. Researchers at the University of Minnesota have found new evidence for how this happens by examining how the thickness of a biofilm produced by Geobacter sulfurreducens affects electron transfer. They used spectroscopic methods involving ultraviolet and visible light with a potentiometric system that exposes the biofilm to a controlled voltage. The investigators discovered that a gradient of electrons developed if the biofilm grew beyond a few cell thicknesses. This gradient was identified when an increased potential, i.e., an increased pull on the electrons produced by a more positive electrode, could not increase the rate electrons traveled out of the thicker biofilm. Unlike thin biofilms where only a small percentage of cytochromes retained electrons, the thicker biofilm showed a substantial number of cytochromes still retained electrons, even when subjected to increased voltage. These results will be helpful in developing new interaction models of metallic contaminants with microbial communities in the environment, particularly in light of the fact that previous studies have led to significantly different descriptions of how the electron transfer process works.
Liu, Y., and D. R. Bond. 2012. “Long-Distance Electron Transfer by G. sulfurreducens Biofilms Results in Accumulation of Reduced c-Type Cytochromes,” ChemSusChem 5(6), 1047–1053. DOI: 10.1002/cssc.201100734.