A four-terminal non-linear dielectric spectrometer was constructed and used to demonstrate that the purple photosynthetic bacterium Rhodobacter capsulatus is able to transduce the energy from a sinusoidally modulated electrical field so as to produce harmonics. Harmonics were produced only by intact cells, and the pattern of harmonics produced depended on whether photosynthetic electron transport was occurring. Through the use of specific inhibitors it was possible to show that the photosynthetic electron transport chain, and not the F 0 F 1 -type H + ATP synthase, was the major contributor to the non-linear dielectric behaviour observed.
