A method to stably immobilize microbes on electrodes was developed. Resting cells of Methylobacterium extorquens AM1(MeAM1) were caged within multiwalled carbon nanotubes (mwNTs)by adding the cells to a water dispersion of MWNTs then allowing the resulting mixture to dry on electrodes. The MeAM1-MWCNTs electrode thus obtained displayed excellent activities in the bidirectional bioelectrocatalysis due to formate dehydrogenase (s) in the resting cells; formate oxidation and carbon dioxide reduction proceeded at steady-state catalytic current densities of 0.6 +/- 0.1 and -0.8 +/- 0.1 mA cm(-2), respectively, using methyl viologen as mediator under very mild conditions (pH 7.0, atmospheric pressure, and 37 degrees C). In addition, the catalytic signal was stable for more than one week under continuous operation.