Photosystems of plants or photosynthetic microorganisms have a function to split water molecules to produce electrons. This paper describes a trial to draw photosynthetically generated electrons out from the microorganisms to produce electricity by using a electron transfer mediator. Such devices, which we call microbial fuel-cells, enable us to convert light energy to electricity directly. A microbial fuel-cell containing a marine alga and 2-hydroxy-1, 4-naphthoquinone as a mediator has been discussed and the conversion efficiency from light energy to electricity has been estimated from the comparison between output current and the amount of oxygen evolved.
