Chapter 9 Substrate oxidation and NAD+ reduction by phototrophic bacteria

Abstract

This chapter discusses substrate oxidation and NAD + reduction by phototrophic bacteria. Anoxygenic phototrophic bacteria (anoxyphotobacteria) cannot use water as an electron donor during photosynthesis. This is in contrast to the oxygenic photosynthesis carried out by higher plants, algae and cyanobacteria, in which water is oxidized to 0. The phototrophic bacteria rely instead on the oxidation of reduced inorganic and simple organic compounds to supply the reducing equivalents needed for the biosynthesis of cellular material via such processes as CO 2 fixation and N 2 fixation. The five families of phototrophic bacteria differ widely with respect to their energy and carbon metabolism and can be divided into two major groups on the basis of their principal electron donors. In the organotrophs, organic compounds are the favored electron donors, while the lithotrophs are characterized by the oxidation of reduced sulphur compounds. Photo-organotrophic growth with a variety of organic compounds is common for the purple non-sulfur bacteria and the green gliding bacteria. In these bacteria, oxidation of substrates that are more reduced than cell material requires the presence of a terminal electron acceptor that is more oxidized than the cell material synthesized. Photolithotrophic growth with reduced inorganic compounds of greatest importance, reduced sulfur compounds) characterizes the purple sulphur bacteria and the green sulfur bacteria.