A 35-fold enhancement in photocurrent generation of Synechocystis sp. PCC 6803 by outer membrane deprivation

Abstract

Biophotovoltaics (BPV) is an emerging technology developed to utilize reducing equivalents produced by photosynthetic organisms. It generates electrical power by exploiting a phenomenon called extracellular electron transfer (EET), where reducing equivalents are transferred extracellularly to exogenous electron acceptors. Although cyanobacteria have been extensively studied in BPV because of their high photosynthetic activity and ease of handling, their extremely low EET activity remains a limitation. In this study, we achieved a 35-fold enhancement in photocurrent generation of the cyanobacterium Synechocystis sp. PCC 6803 by deprivation of the outer membrane, where electrons are suggested to stem from NADPH; this, along with a significantly higher rate of exogenous ferricyanide reduction, verified that low permeability of the outer membrane contributues to low cyanobacterial EET activity. Moreover, outer membrane deprivation enhanced extracellular derivation of reducing equivalents serving as respiratory substrates for other heterotrophic bacteria, making it promising and useful for effective derivation of reducing equivalents.