Giving Bacteria An Electrifying ‘Armor’

Coating bacteria in a conductive polymer not only increases the efficiency of electron transfer but also helps them survive better in microbial fuel cells.

AsianScientist (July 10, 2017) – Wrapping live bacteria in a layer of conducting polymer can improve their ability to generate electricity. These findings have been published in Angewandte Chemie.

In the early the 20th century, scientists connected bacteria cells with electrodes to generate electricity. The principle is that, if no oxygen is present, the bacteria’s metabolism changes to produce protons and electrons instead of carbon dioxide and water. These electrons can be used for current generation in an electrochemical cell.

However, the power density of such microbial fuel cells has been unsatisfactory thus far. Much of the electrochemical potential of the bacteria is wasted because the electrons produced are not easily transmitted to the electrode.

To make the bacteria more conductive, Associate Professor Zhang Qichun and his colleagues from Nanyang Technological University explored the idea of encasing bacteria in a shell of an electron-conducting polymer called polypyrrole. This proved to be a challenge as the coated bacteria must still be viable for the fuel cell to work.

“The modification of bacterial cells with polypyrrole is anticipated to improve the electrical conductivity of bacterial cells without reducing their viability,” the authors explained.

The researchers used iron ions as the oxidative initiator to polymerize pyrrole monomers on the bacterium’s surface. The organism of choice was the proteobacterium Shewanella oneidensis, which is known for its metal toleration and both aerobic and anaerobic lifestyles.

Still living and active, the coated bacteria were tested for biocurrent generation with a carbon anode. Compared to their unmodified counterparts, they displayed a 23 times smaller resistance (which means, enhanced conductivity), a five-fold increase in electricity generation, and 14 times higher maximum power density of the anode in a microbial fuel cell.

Moreover, if the bacteria were fed with lactate, the authors observed a pronounced current, which did not happen when uncoated bacteria were used.

Zhang’s approach is a remarkable solution to the conductivity problem of a microbial anode. The authors believe that this coating scheme of live bacteria may add a new dimension to the exploration of microbial fuel cells, as well as general research on cell-surface functionalization.

The article can be found at: Song et al. (2017) Living and Conducting: Coating Individual Bacterial Cells with In Situ Formed Polypyrrole.


Source: Wiley; Photo: Shutterstock.
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