Photo-induction of electrical current with the cyanobacteriumAgmenellum quadruplicatum PR-6

We investigated the possibility of eliciting a measurable photoinduced electrical current from the cyanobacteriumAgmenellum quadruplicatum PR-6 (Synechococcus PCC 7002). This proved virtually impossible for intact cells. However, treated PR-6 cells fixed in an alginate matrix on tin oxide as the active electrode in a three electrode electrochemical cell gave rise to a significant light response. Cell treatments involving toluene, chloroform or detergents were effective and gave current responses up to 250 nA. Drying the cyanobacterial matrix increased the current yield at least fifty-fold. These effects were observed for light wavelengths > 650 nm and were not influenced by inhibitors or enhancers of photosynthesis nor by sustained argon bubbling of the electrolyte.French pressure cell lysates facilitated distinction between two light induced current components. Lysates prepared without CaCl₂ gave current induction kinetics that were indistinguishable from those on chemically treated cells i.e. slowly rising to a stable maximum in 10–15 min. When CaCl₂ was present during lysis, a rapidly induced (<1 s) unstable component was observed. Toluenization of PR-6 either prior to or post lysing abolished the CaCl₂ related effect. CaCl₂ had no effect on current induction in strain PR-6008, which lacked the and subunits of phycocyanin and exhibited slow current induction kinetics.The observed effects are interpreted as responses of components of the photosystems of PR-6 rather than in terms of an integrated photosynthetic process.