The Electric Microbe
#1

The Electric Microbe
Vishnu.R & Ramesh K.R
Department Of Electronics and Instrumentation Engineering
Noorul Islam College Of Engineering

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Abstract
Electric microbe is the latest invention which is used to generate electricity from mud and
wastewater. Bacteria have always gotten a bad rap. But we should be thankful for one especially
talented microbe, Geobacter, which has tiny hair like extensions called pili that it uses to
generate electricity from mud and wastewater.

Introduction:
Scientists have discovered a tiny biological
structure that is electrically conductive, which could
help clean up groundwater and produce electricity
from renewable resources. The conductive
structures, known as "microbial nanowires," are
produced by a microorganism known as Geobacter.
The very small nanowires are only 3-5 nanometers
in width (20,000 times finer than a human hair), but
quite durable and more than a thousand times long
as they are wide.
Geobacter are the subject of intense investigation
because they are potentially useful agents in the
bioremediation of groundwater contaminated with
pollutants such as toxins, radioactive metals or
petroleum. They also have the ability to convert
human and animal wastes or renewable biomass
into electricity. This new research shows
how Geobacter transfers electrons outside the cell
onto metals or electrodes to achieve these
processes. These results help us understand how
Geobacter can live in environments that
Lack oxygen and carry out such unique phenomena
as removing organic and metal pollution from
groundwater.

Previous studies showed that Geobacter produces
fine, hair like structures, known as pili, on just one
side of the cell. A team in 2009 speculated that
the pili might be miniature wires extending from
the cell that would permit Geobacter to carry out its
unique ability to transfer electrons outside the cell
onto metals and electrodes. This was confirmed in a
study using an atomic force microscope which
found the pili were highly conductive. Such long,
thin conductive structures are unprecedented in
biology. This completely changes our concept of
how microorganisms can handle electrons, and it
also seems likely that microbial nanowires could be
useful materials for the development of extremely
small electronic devices. Manufacturing nanowires
from more traditional materials such as metals,
silica, or carbon is difficult and expensive.
However, it is easy to grow billions
of Geobacter cells in the laboratory and harvest the
microbial nanowires that they produce. The
researchers added that by altering the DNA
sequence of the genes that encode for microbial
nanowires, it may be possible to produce nanowires
with different properties and functions.
The remarkable and unexpected discovery of
microbial structures comprising microbial nanowires that may enable a microbial community
in a contaminated waste site to form mini-power
grids could provide new approaches to using
microbes to assist in the remediation of DOE waste
sites; to support the operation of mini-
environmental sensors, and to nano-manufacture in
novel biological ways. This discovery also
illustrates the continuing relevance of the physical
sciences to today's biological investigations," said
Aristides Patrinos of the U.S. Department of
Energy, which funds the Geobacter research.

Background of The Invention:
The basic hydrogen PEM fuel cell consists of two
catalyst-loaded electrodes separated by a proton
exchange membrane (PEM). Molecular oxygen
supplied to the catalytically active cathode is
dissociated and reduced to O2- (an energetically
favored process). Molecular hydrogen supplied to
the anode is dissociated and the hydrogen atoms
oxidized to protons (H.sup.+), giving Up their
electrons to the anode. Those electrons propagate
through the external circuit to the cathode,
delivering work in the process. The protons
generated at the anode meanwhile diffuse through
the PEM to combine with the reduced oxygen,
producing water and heat as the waste products.
Both the anode and cathode (in addition to the
requirement that they be electrically conductive) are
engineered with specific catalysts, commonly Pt, to
facilitate the molecular dissociations and the
respective electron transfers.

Conversion of Organic Matter To
Electricity:

Recent studies have greatly expanded the range of
microorganisms known to function either as
electrode-reducing microorganisms at the anode or
as electrode-oxidising microorganisms at the
cathode. Microorganisms that can completely oxide
organic compounds with an electrode serving as the
sole electron acceptor are expected to be the
primary contributors to power production.
Several mechanisms for for electron transfer via
outer-surface c-type cytochromes,long range
electron transfer via microbial nanowires, electron
flow through a conductive biofilm matrix
containing cytochromes, and soluable electron
shuttles. Which mechanisms are most important
depand on the microorganisms and the thickness of
the anode biofilm. Emerging systems biology
approaches to the study, design, and evolution of
microorganisms interacting with electrodes are
expected to contribute to improved microbial fuel
cells.

Conclusions:
Although the microbiology of microbe-electrode
interactions is fascinating from a purely biological
perspective, most research in this area is ultimately
justified by the hope of increasing the power output
of microbial fuel cells or developing additional
microbe-electrode applications. Just as there is a
wide phylogenetic diversity of microorganisms
capable of extra cellular electron transfer to Fe(III),
it is likely that there is an equally diverse range of
microorganisms capable of interacting with
electrodes. If the appropriate strategies can be
capable of higher rates of electron transfer between
microorganisms and electrodes than currently
available strains. Genome-scale metabolic modeling
coupled with genetic engineering may yield strains
that can enhance current production. The capacity
to produce current production is a promising
approach for increasing the power output of
microbial fuel cells. Further more, as the
understanding of the range of reactions that
microorganisms can carry out with electrodes
serving either as the electron donor or the electron
acceptor continues to expand the applications of
microbe-electrode interaction and production of
commodity chemicals may eclipse Power
production as the most promising uses of this
technology.
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