Detection of chemically-induced dynamic electron polarisation (CIDEP) in whole cells and membrane fractions of Chlorobium limicola f. thiosulphatophilum

Chemically-induced dynamic electron polarisation (CIDEP) in photosynthesis was first observed as strongly-polarised transient electron paramagnetic resonance (EPR) signals in spinach chloroplasts at room temperature. These polarised signals (e.g., non-Boltzmann population of the electron spin sub-levels) are proposed to arise from the photosystem I reaction centre via generation of a nascent radical pair during electron transfer from the excited singlet state of the primary electron donor P700. The authors report EPR transients exhibiting CIDEP in whole cells and membrane fractions of the green sulphur bacterium C.l. f. thiosulphatophilum at cryogenic temperatures. These signals do not arise from reaction centres analogous to those found in purple photosynthetic bacteria, as the preparations were not exposed to SDS, other detergent or denaturing agent. These results show that a reaction centre in green photosynthetic bacteria resembles photosystem I of cyanobacteria and higher plants.