Guide

Main Module | Energy from Mud? Thank a Microbe!
15
Background
backGrouNd
Other organisms, particularly certain types of bacteria, are able to respire without
oxygen being present. This is called anaerobic (without oxygen) respiration.
Organisms that metabolize when oxygen is not present are called anaerobes. When
oxygen is not present the electrons are taken up by elements other than oxygen,
particularly metals like iron and sulfur.
For most organisms these processes happen
inside the organisms’ cells but there is one
type of bacteria that can actually give off
electrons to something outside of their
cells! These special bacteria are called
electrogenic bacteria. It is these electrogenic
bacteria that are the key to how a microbial
fuel cell works!!
Electrogenic bacteria occur naturally and are abundant in nearly all types of soil,
mud, sewage and waste water which is why microbial fuel cells can be made pretty
much anywhere,
Two common types of electrogenic bacteria are: Shewanella (Mr. Clean), and
Geobacter (The Iron-Breather):
ChemistryConnection!
Metals and other materials
change their chemical form when
used as electron acceptors, and
become less toxic.
QuickRecap!
1. When Microbes
breakdown organic
matter in anaerobic
(lacking oxygen)
environments, materials
such as sulfur and iron
are used as electron
acceptors.
2. Certain bacteria give off
their electrons outside of
their body.
3. Metals and other
materials change their
chemical form when used
as electron acceptors and
become less toxic.
Shewanella (Mr. Clean)
Known for their versatility, Shewanella
species can be found almost everywhere on
earth, from mountain dirt to ocean sediments.
Due to their unique ability to expel electrons to
compounds outside their bodies, Shewanella can
metabolize a variety of substances and link together
through conductive appendages, transferring
electrons to their neighbors. They can even metabolize
toxic compounds containing radioactive Uranium!
eaer (he rnreaher)
Geobacter species have the ability to respire
iron compounds and use them in a way similar
to the way humans respire oxygen. In fact, they
prefer to live in environments where there is no oxygen,
such as deep underground or within ocean sediments.
Like Shewanella, due to their ability to expel electrons,
they can metabolize many environmental pollutants,
including petroleum and Uranium, and have been used
to help clean up pollution.
Geobacter (The Iron-Breather)