During the last few years we have proven that viable bacterial cells can be electrochemically ”wired” to electrodes with flexible Os^2+/3+ functionalised polymers such as poly(1-vinylimidazole)₁₂-[Os(4,4’-dimethyl-2,2’-dipyridyl)₂Cl₂]^2+/3+ and poly(vinylpyridine) [Os(N,N’-dimethyl-2,2’-biimidazole)₃]^2+/3+. Our initial studies¹ in this field were made with the structurally rather simple gram-negative Gluconobacter oxydans, where we addressed redox enzymes from the cytoplasmic membrane yielding response for glucose, fructose, ethanol and glycerol. In further studies focus was on the structurally more complex gram-negative Pseudomonas putida and Pseudomonas fluorescens,^2,3 where response currents could be obtained both for substrates being metabolised in the cytoplasmic membrane (glucose) as well as in the cytosol of the cell (phenol). Recently we have also showed that introduction of a cytochrome to the cytoplasmic membrane of E. coli greatly facilitated the communication between these gram-negative bacterial cells and the osmium polymers.⁴ In the current study reported here⁵, we now use the gram-positive model organism B. subtilis, with a substantially thicker peptidoglycan cell wall, which at an early glance is expected to be more difficult to permeate by the osmium polymeric mediators. In B. subtilis the cell wall has a diameter of ≈35 nm. It constitutes a multilayered structure composed mainly of peptidoglycan and teichoic acids. The polyelectrolytic properties of the peptidoglycan and teichoic acids provide a continuum of anionic charge between the cytoplasmic membrane and the environment. These properties of the cell wall may facilitate the connection between the cells and the polycationic Os-polymer and further to the electrode. Using a B. subtilis strain which overproduces succinate:quinone oxidoreductase (respiratory complex II), we were able to improve the current response several fold using succinate as substrate. We believe that the approach taken in this work adds to the understanding of how gram-positive cells may communicate with their surroundings through electron conductive structures present in the layers of peptidoglycan/teichoic acids. This is also in line with the recent hypothesis raised by Ehrlich⁶ on that electron conducting structures are present in the periplasm of gram-positive bacteria (peptidoglycan, teichoic acids), which must be responsible for conveying electrons from the cytoplasmic membrane to the outer surface of the cell wall. Another recent publication that support such a theory is the work by Marshall and May⁷, who show that gram-positive Thermincola ferriacetica strain Z-0001 readily can grow onto a graphite electrode and exhibit direct electron transfer communication.

[1] Vostiar, I.; Ferapontova, E. E.; Gorton, L. Electrochem. Commun. 2004, 6, 621-626.

[2] Timur, S.; Haghighi, B.; Tkac, J.; Pazarlioglu, N.; Telefoncu, A.; Gorton, L. Bioelectrochemistry 2007, 71, 38-45.

[3] Timur, S.; Anik, U.; Odaci, D.; Gorton, L. Electrochem. Commun. 2007, 9, 1810-1815.

[4] Alferov, S.; Coman, V.; Gustavsson, T.; Reshetilov, A.; von Wachenfeldt, C.; Hägerhäll, C.; Gorton, L. Electrochim. Acta 2009, 54, 4979-4984.

[5] Coman, V.; Gustavsson, T.; Finkelsteinas, A.; von Wachenfeldt, C.; Hägerhäll, C.; Gorton, L. submitted.

[6] Ehrlich, H. L. Geobiology 2008, 6, 220-224.

[7] Marshall, C. W.; May, H. D. Energy Environ. Sci. 2009, 2, 699-705.

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