Electron Transport Chains of Phototrophically and Chemotrophically Grown Chloroflexus Aurantiacus

Summary

The photosynthetic gliding green bacterium Chloroftexus aurantiacus is capable of both phototrophic and chemotrophic growth (Sprague et at., 1981). Cells grown under phototrophic conditions contain BChl a associated with the cytoplasmic membrane plus antenna BChl c located in chlorosomes attached to the cytoplasmic side of the cell membrane (Pierson and Castenholz, 1976). During chemotrophic growth chlorophyll synthesis is repressed and the number of chlorosomes decline (Sprague et at., 1961). Synthesis of pigment-binding polypeptides and of electron carrier proteins such as Cyt “c554” the immediate electron donor to the reaction center P870^-, has been shown to be controlled by O₂ tension in Chloroftexus (Foster et al., 1965; Bruce et al., 1982; Wynn et al., 1987). Other aspects of the cytochrome content of Chloroftexus, particularly the Cyt b:Cyt c ratio and the presence of heme a, have been shown to vary with growth conditions (Bruce et at., 1982; Wynn et at., 1987; Pierson, 1985; Zannoni and Ingledew, 1986; Zannoni, 1986). We have characterized the membrane-bound components of the electron transfer chains of both phototrophicatly and chemotrophicalLy grown Chloroftexus. Particular attention has been placed on the cytochrome and iron-sulfur center content of chemotrophically grown cells, cultured under conditions of vigorous aeration in the dark (Foster et al., 1966; Wynn et al., 1987). Cells grown under these conditions are completely free of BChl c and contain < 0.02% of the BChl a found in cells grown anaerobicalLy in the Light.