The idea of
using microorganisms to unlock the energy present
in waste products has been around since the 1980s,
but its application has been held back by problems
such as the inefficiency of the bacteria used
at converting waste sugars to electricity. Now,
all that could change in the light of work published
in Nature Biotechnology describing an efficient
biofuel cell that uses the recently isolated bacterium
Rhodoferax ferrireducens.
Biofuel cells
harness the ability of bacteria to remove electrons
from organic compounds and transfer them to an
electron acceptor. In the case of biofuel cells,
the acceptor is a graphite anode and the electrons
that are transferred produce an electric current
that can power a so- called 'bacterial battery'.
But the bacteria tested so far for this application
have had drawbacks, such as inefficiency in ustng
the electrons available from their substrates
or a requirement for unstable electron-shuttling
compounds to transfer electrons to the anode,
reducing the useful life of the fuel cell. Now,
Derek Lovley and his colleague Swades Chaudhuri
have overcome these problems using an R. ferrireducens
biofuel cell with glucose as a substrate. They
obtained an electron-transfer efficiency of over
80% - a substantial improvement on the average
efficiency of -10% using other bacteria. R.
ferrireducens can also transfer electrons
directly to the anode, bypassing the need for
electron-shuttling compounds, which cuts costs
and enables a longer-term use of the fuel cell.
Another advantage
of using R. ferrireducens in biofuel
cells is its ability to produce electricity from
a range of substrates - as well as glucose, it
can strip electrons from other carbohydrates such
as xylose, which is generated in large quantities
in the production of paper.
The amount of
current that Lovley and Chaudhuri generated from
the R. ferrireducens fuel cell was too
small to have a practical use at the moment, and
modifications to the design are needed to improve
on this. Steps such as changing the material used
to make the anode and increasing its surface area
should increase the power generated, bringing
us one step closer to using bacterial batteries
as an efficient way of disposing of waste biomass.
(Courtesy: article published
in Nature Reviews Microbiology).
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