Precise structure of proteins, which allow certain bacteria to move electrical charges outside the cell membrane

Batteries of tomorrow might have a heart “alive”. A team of University of East Anglia (UEA) 1 in the UK, in collaboration with Pacific Northwest National Laboratory, U.S., presented the first precise structure of proteins, which allow certain bacteria to move electrical charges outside the cell membrane.

The discovery, published in Proceedings of the National Academy of Sciences (PNAS 3), is an important step forward in the development of revolutionary applications. Specifically, the researchers hope to succeed “bind” these bacteria to electrodes, with the purpose of development of efficient bio-batteries or even use for remediation of areas contaminated with heavy metals. “It is an exciting step forward on the road to deciphering how certain bacterial species moving electrons inside and outside the cells, “said Tom Clarke, coordinator of the School of Biological Sciences, University of East Anglia.

Who are these strange bacteria-electricians? Researchers have focused on some copies of Shewanella oneidensis, a bacterium present in soil and lake sediments, which can survive under anaerobic conditions, meaning without oxygen. These bacteria adopt a respiration cellular system based on electron transfer which come into contact with metals. Acceptance of electrons by metals, a chemical process called “reduction”, provides bacteria the energy required.

Clarke and colleagues studied the bacteria in question since 2009 when they discovered that Shewanella can build filaments of proteins, separated by iron atoms. These filaments, with nanometric dimensions, is acting like electrical wires, being able to carry electrons outside the cell membrane. In their new study, scientists have used sophisticated techniques of X-ray crystallography to study in detail the structure of this protein bio-circuit, focusing on membrane proteins present in bacteria.

Precisely the molecular structure of these proteins, measuring a few millionths of a millimeter, subsequently allowed researchers to develop several models to describe the dynamics of electron transfer. “Identifying the precise molecular structure of key proteins involved in this process is essential for the future use of microbes as a source of electricity, ” said Clarke. Applications of this bacteria is not restricted to achieve bio-batteries. Shewanella oineidensis convert heavy metals into non-soluble form, preventing dissolution in water, and groundwater contamination.