Isolated photosystems and sub-cellular photosynthetic fractions may be able to directly reduce the anode if the biological redox components are close enough to the electrode for electron transfer to occur.[1] In contrast to organisms such as dissimilatory metal reducing bacteria, algae and cyanobacteria are poorly adapted for extracellular electron export - no molecular mechanisms enabling direct reduction of an insoluble extracellular electron acceptor have been conclusively identified. Nevertheless, a low rate of anode reduction has been observed from whole photosynthetic organisms without the addition of exogenous redox-active compounds.[2][11] It has been speculated that electron transfer occurs through the release of low concentrations of endogenous redox mediator compounds.