Sulfur bacteria, photosynthesis

Flowever, many photosynthetic bacteria, such as purple sulfur and green sulfur bacteria contain special bacteriochlorophyll compounds (not chlorophyll a) and carry out anoxygenic photosynthesis without producing oxygen ... 

A study of photosynthetic organisms other than green plants has revealed that certain bacteria, such as the purple sulfur bacteria, utilize H2S instead of H20 as a reductant in photosynthesis. The product obtained is elemental sulfur instead of oxygen ... 

Prokaryote heterotrophs precursors of cyanobacteria. Stromatolites. Sulfur bacteria Beginning of photosynthesis Traces... 

The Fe-S Reaction Center (Type I Reaction Center) Photosynthesis in green sulfur bacteria involves the same three modules as in purple bacteria, but the process differs in several respects and involves additional enzymatic reactions (Fig. 19-47b). Excitation causes an electron to move from the reaction center to the cytochrome bei complex via a quinone carrier. Electron transfer through this complex powers proton transport and creates the proton-motive force used for ATP synthesis, just as in purple bacteria and in mitochondria. 

Role of H2S in Some Photosynthetic Bacteria Illuminated purple sulfur bacteria carry out photosynthesis in the presence of H20 and 14C02, but only if H2S is added and 02 is absent. During the course of photosynthesis, measured by formation of [14C]carbohydrate, H2S is converted to elemental sulfur, but no 02 is evolved. What is the role of the conversion of H2S to sulfur Why is no 02 evolved ... 

Hydrogen sulfide is also subject to phototrophic oxidation in anaerobic environments. The photosynthetic sulfur bacteria Chromatiaceae, Ectothiorho-dospimceae, and Chlorobiaceae can photoreduce C02 while oxidizing H2S to S, in a striking analogy with the photosynthesis of eukaryotes ... 

When purple non-sulfur bacteria switch from photosynthesis in the light to respiration in the dark, the content of BChl a or is diminished, and the synthesis of cytochrome oxidase is increased [101]. In some bacteria, such as Rb. sphae-roides, two oxidases are formed, Cyt aa [90] and Cyt o. In most others (e.g. R. rubrum) only Cyt o is formed [97]. Work during the past decade has revealed a strong similarity between the electron transfer pathways in purple non-sulfur bacteria and in the mitochondrial inner membrane [92]. 

Many phototrophs do not produce O2 as a waste product. Such anoxygenic phototrophs are comprised of purple sulfur, purple nonsulfur, green sulfur, and green nonsulfur bacteria. Although purple sulfur bacteria are typically found in anoxic zones of lakes and sediments, many are capable of photosynthesis under oxic conditions (Van Gemer-den, 1993). Most fix N2 and store S° intra- or extracellularly, and some are capable of chemo-lithoautotrophic growth. Extreme halophilic, sulfi-dic, and mildly thermophilic environments harbor... 

A variant of photosynthesis occurs in certain environments where sulfide (S2-) is present and anaerobic conditions exist (i.e., there is no molecular oxygen, 02, present). In this case, sulfide can be used as a reductant in place of water, and the photosynthetic process is performed by colored (green or purple) sulfur bacteria ... 

Fig. 10. Top Charge recombination reactions in photosystem I (left) and in the reaction center of green-sulfur bacteria (right). Bottom Flash-induced absorbance changes and kinetics of charge recombination in the dark. [The left panel is reproduced from Fig. 3 (A). Data in lower, right panel are taken from Kusumoto, Inoue and Sakurai (1995) Spectroscopic studies of bound cytochrome c and an iron-sulfur center in a purified reaction center from the green sulfur bacterium Chlorobium tepidum. Photosynthesis Res 43 109.

Evolution of photosynthesis was one of the most important biological events of the early Earth s history. Anaerobic pbotosyntbetic bacteria, like tbe modem green and purple sulfur bacteria, would have been tbe first pbotosyntbetic organisms. There is no remarkable evidence of tbe development of these organisms before 3.0-3.5 billion years ago, however, the process of anaerobic photosynthesis is thought to have occurred before this time. The following speculations can prove this hypothesis. 

Anoxic photosynthesis utilizes light energy, but does not produce oxygen. Green and purple bacteria of the sulfur and nonsulfur kind are anoxic photosynthesizers. The sulfur bacteria oxidize sulfide to elemental sulfur and can even oxidize it further to sulfate. 

The green sulfur bacteria (Chlorobium) are only distantly related to other phyla of bacteria. The fact that they utilize photosynthesis shows, however, that photosynthesis must have developed at an early stage of bacterial evolution. 

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