Fluorescence detected magnetic resonance (FDMR) of green sulfur photosynthetic bacteria Chlorobium sp.

Fluorescence Detected Magnetic Resonance (FDMR) spectra have been measured for whole cells and isolated chlorosomal fractions for the green photosyntheic bacteria Chlorobium phaeobacteroides (containing bacteriochlorophyll e, and isorenieratene as major carotenoid) and Chlorobium limicola (containing bacteriochlorophyll c, and chlorobactene as major carotenoid). The observed transition at 237 MHz (identical in both bacteria) and > 1100 MHz can be assigned, by analogy with published data on other carotenoids, to the 2E and D + E transitions, respectively, of Chlorobium carotenoids. Their zero field splitting (ZFS) parameters are estimated to be: |D|=0.0332 cm^–1 and |E|=0.0039 cm^–1 (chlorobactene), and |D|=0.0355 cm^–1 and |E|=0.0039 cm^–1 (isorenieratene). In the intermediate frequency range 300–1000 MHz the observed transitions can be assigned to chlorosomal bacteriochlorophylls c and e, and to bacteriochlorophyll a located in the chlorosome envelope and water-soluble protein. The bacteriochlorophyll e triplet state measured in 750 nm fluorescence (aggregated chlorosomal BChl e) is characterised by the ZFS parameters: |D|=0.0251 cm^–1 and |E|=0.0050 cm^–1.Abbreviations BChl - bacteriochlorophyll - BPh - bacteriopheophytin - Chl. - Chlorobium - F(A)(O)DMR - fluorescence (absorption) (optical) detected magnetic resonance - FF - fluorescence fading - ISC - intramolecular intersystem crossing - RC - reaction center - ZFS - zero field splitting