Bioenergetic Strategies of the Sulfate-Reducing Bacteria

Abstract

It has become evident that the basic chemiosmotic mechanisms that govern electron transfer-coupled phosphorylation, including photophos-phorylation and oxidative phosphorylation, must have evolved under anoxic conditions existent in the early environment of earth. In this anaerobic environment there does not appear to have been a single major energy source, and it is possible that a diversity of bioenergetic systems evolved around specific redox couples, such as H₂/S°, H₂/CO₂, CO/SO₄²⁻, etc. Thermodynamically, these reactions do not provide for biosynthesis of large amounts of ATP, and growth of most anaerobes is generally viewed as being severely limited by ATP availability. With the advent of photosynthetic systems and subsequent generation of an oxygen atmosphere, evolution became focused upon higher-yielding, ATP-generating systems involving light and oxygen, resulting in loss of the rich diversity of anaerobic bioenergetic systems from the metabolic potential of most photosynthetic and aerobic prokaryotes and eukaryotes.