Biochemistry of the chemolithotrophic oxidation of inorganic sulphur

A historical review is presented of the elucidation of the mechanisms of oxidation of inorganic sulphur compounds and of electron transport in the thiobacilli. A unitary mechanism, consistent with current knowledge, is proposed. The significance of polythionates is discussed. The relations between oxidation mechanisms, substrate-level and electron transport-dependent phosphorylation, energy-dependent NAD+ reduction and efficiency of growth are assessed in order to evaluate the efficiency of energy conservation in different species. The unresolved problems are identified for the benefit of those planning further assaults on the last redoubts of the thiobacilli.