Sulfur and light?: History and "Thiology" of the phototrophic sulfur bacteria

This chapter describes how our present knowledge of sulfur metabolism of phototrophic sulfur bacteria accumulated through several major steps of experimental progress. Among these are the following: discovery of microbial cells with conspicuous inclusions ("purple" bacteria and colorless ones); verification that such inclusions consist of sulfur; detection of phototactic behavior in purple bacteria; enrichment cultures ("Winogradsky columns"), consequent detection of sulfide requirement and of the liquid stage of sulfur inclusions, "globules"; identification of the pigments as bacteriochlorin (now chlorophylls) and bacterioerythrin (now carotenoids); discovery of Chlorobium, a green bacterium that deposits sulfur globules outside its cells; discovery of photosynthesis in purple non-sulfur bacteria; postulation of a photosynthetic metabolism in purple sulfur bacteria by combination of photosynthesis and chemosynthesis; evidence that the red ("purple") and green sulfur bacteria perform anaerobic photosynthesis (carbon dioxide fixation) dependent on the oxidation of reduced sulfur compounds; discovery of Ectothiorhodospira, a halophilic phototrophic purple sulfur bacterium that deposits sulfur globules outside its cells; systematic development of enrichment and pure culture media and techniques for the Chromatiaceae and Chlorobiaceae; the first specific studies on sulfur metabolism in purple bacteria on whole cells and crude extracts; purification of adenosine 5'-phosphosulfate reductase and reverse siroheme sulfite reductase; finding and purification of sulfide quinone reductase; discovery and characterization of the dsr gene cluster in Allochromatium vinosum; isolation and gene sequence of the sulfur globule encoating periplasmic proteins in Chromatiaceae; determination of the inner structure of the sulfur globules by X-ray absorption near-edge spectroscopy in phototrophic and chemotrophic sulfur bacteria; characterization of sulfite oxidoreductase; characterization of the thiosulfate-oxidizing (Sox) multienzyme complex in Allochromatium vinosum.