The Role of Type IV Pili of Synechocystis sp. PCC 6803 in Extracellular Electron Transfer

Abstract

The objective of this research was to determine whether the Type IV pili of Synechocystis sp. PCC 6803 are involved in electron donation to the extracellular environment. In conjunction with the current theories and published observations from other research groups, the findings presented in this research are suggestive of interplay between both the photosynthetic and respiratory electron transport chains and the pili. Gene deletion studies also advocate possible cytochrome intermediates interacting within the electron transport chain of both the photosynthetic and respiratory complexes, involved in donating electrons to the pili. The construction and implementation of four novel instruments has been outlined in this project, consisting of: (1) a small battery powered spectrophotometer capable of measuring turbidity of liquid culture, (2) solid-grown-culture density plate-reader, (3) chlorophyll concentration fluorometer and (4) an apparatus that measures voltage indicative of electron donation to an iron electrode. The physiological characterisation component of this project explored the function of the Type IV pili in Synechocystis sp. PCC 6803 in facilitating electron donation to extracellular acceptors. A link has been observed between oxidized iron minerals and the presence of these pili and cytochromes suggesting that they may provide the organism with a utility for sensing iron scarcity. An additional phenotype implies a function of these pili in protecting against oxidative stress by dissipation of excess excitation energy. Together these observations indicate the potential of electron donation by Type IV in Synechocystis sp. 6803, which may be exploited in the future to convert solar energy into electricity.