Effects of light on the electrical output of bioelectrochemical fuel‐cells containing Anabaena variabilis M‐2: Mechanism of the post‐illumination burst

Bioelectrochemical fuel‐cells containing Anabaena variabilis M‐2 and 2‐hydroxy‐1,4‐naphthoquinone (HNQ) produced electricity in the dark. The current output was increased substantially in the light and a burst of the output current occurred upon darkening. There is a linear relationship between the coulombic output in the burst and the preceding light period. Photosynthetic O2 evolution with HNQ as an electron acceptor and the light‐induced generation of the output current were completely inhibited by 1 × 10−4 mol dm−3 carbonyl cyanide m‐chlorophenylhydrazone (CCCP) but 4 × 10−5 mol dm−3 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) inhibited these activities only by 30–40%. Thus, HNQ accepts electrons mainly at the site between photosystem 2 reaction center and QB protein. In the presence of CCCP, the current output was decreased upon illumination and the burst occurred upon darkening. These results suggested that the source of electrons in the burst is a substance(s) accumulated within the Anabaena cells during the light period as a result of inactivation of an enzyme involved in the metabolism of producing output current in the dark.