Primary photochemistry in the facultatively aerobic green photosynthetic bacterium Chloroflexus aurantiacus.

Photochemical activity was examined in membrane fragments and a purified membrane preparation from Chloroflexus. Flash-induced absorption difference spectroscopy strongly suggests a primary donor (P(865)) that is more similar to the P(870) bacteriochlorophyll a dimer found in the purple photosynthetic bacteria than it is to P(840) found in the anaerobic green bacteria. Redox measurements on P(865) and an early acceptor also indicate a photochemical system characteristic of the purple bacteria. The membrane preparation contains a tightly bound type c cytochrome, c(554), that is closely coupled to the reaction center as indicated by its ability to rereduce photooxidized P(865). Chloroflexus thus appears to be distinct photochemically from other families of photosynthetic bacteria and may occupy an important role in photosynthetic evolution.