  Since the 1970's, when the Viking spacecrafts carried out experiments aimed
to the detection of microbial metabolism on the surface of Mars, the search for
nonspecific methods to detect life in situ has been one of the goals of
astrobiology. It is usually required that the methodology can detect life
independently from its composition or form, and that the chosen biological
signature points to a feature common to all living systems, as the presence of
metabolism. In this paper we evaluate the use of Microbial Fuel Cells (MFCs)
for the detection of microbial life in situ. MFCs are electrochemical devices
originally developed as power electrical sources, and can be described as fuel
cells in which the anode is submerged in a medium that contains microorganisms.
These microorganisms, as part of their metabolic process, oxidize organic
material releasing electrons that contribute to the electric current, which is
therefore proportional to metabolic and other redox processes. We show that
power and current density values measured in MFCs using microorganism cultures
or soil samples in the anode are much larger than those obtained using a medium
free of microorganisms or sterilized soil samples, respectively. In particular,
we found that this is true for extremophiles, usually proposed to live in
extraterrestrial environments. Therefore, our results show that MFCs have the
potential to be used to detect microbial life in situ.
