title: Photocurrent generation by immobilized cyanobacteria via direct electron transport in photo-bioelectrochemical cells.
abstract: Cyanobacteria possess unique and exciting features among photosynthetic microorganisms for energy conversion applications. This study focuses on production of direct electricity using a cyanobacterium called Nostoc sp. (NOS) as a photo-biocatalyst immobilized on carbon nanotubes on the anode of photo-bioelectrochemical cells. By illuminating with light (intensity 76 mW cm(-2)) the NOS immobilized on a carbon nanotube (CNT) modified electrode generated a photocurrent density of 30 mA m(-2) at 0.2 V (vs. Ag/AgCl). The contribution of different photosynthetic pigments in NOS to the light capture was analyzed and chlorophyll-a was found to be the major contributor to light capture followed by phycocyanin. Further investigation using a set of inhibitors revealed that the electrons were redirected predominantly from PSII to the CNT through the plastoquinone pool and quinol oxidase. A rudimentary design photosynthetic electrochemical cell has been constructed using NOS/CNT on the anode and laccase/CNT on the cathode as catalysts. The cell generated a maximum current density of 250 mA m(-2) and a peak power density of 35 mW m(-2) without any mediator. By the addition of 1,4-benzoquinone as a redox mediator, the electricity generation capability was significantly enhanced with a current density of 2300 mA m(-2) and a power density of 100 mW m(-2). The power densities achieved in this work are the highest among 'non-engineered' cyanobacteria based electrochemical systems reported to date.
authors.affiliation: Nano Electrochemistry Laboratory, College of Engineering, The University of Georgia, Athens, GA 30602, USA. rama@uga.edu.
authors.forename: Narendran
authors.initials: N
authors.lastname: Sekar
authors.forename: Yogeswaran
authors.initials: Y
authors.lastname: Umasankar
authors.forename: Ramaraja P
authors.initials: RP
authors.lastname: Ramasamy
mesh_terms: D016227:Benzoquinones / Q000737:chemistry; D001674:Bioelectric Energy Sources; D018914:Cells, Immobilized / Q000166:cytology / Q000502:physiology; D004560:Electricity; D004566:Electrodes; D004579:Electron Transport; D008027:Light; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000648:ultrastructure; D046937:Nostoc / Q000166:cytology / Q000502:physiology*; D010084:Oxidation-Reduction; D010788:Photosynthesis
chemical_list: D016227:Benzoquinones; D037742:Nanotubes, Carbon; C004532:quinone