Summary
In Chromatium strain 6412 storage carbohydrate synthesized in the light, gradually disappeared in the dark. Simultaneously, poly-β-hydroxybutyric acid (PHB) was produced, CO2 was released and intracellular elemental sulfur was reduced to sulfide. Expressed on a molar base, the ratio between storage carbohydrate monomer (as glucose) consumed, sulfur reduced, PHB monomer produced, and sulfide released was approximately 1 : 3 : 1 : 3. This indicates that sulfur acts electron acceptor in the conversion of storage carbohydrate to PHB. Assuming that in the dark storage carbohydrate is broken down to pyruvate via the Embden-Meyerhoff pathway, whereafter PHB is synthesized from pyruvate via acetyl-CoA and acetoacetyl-CoA, the conversion of storage carbohydrate to PHB results in a net gain of 3 ATP per glycosyl unit converted. Since Thiorhodaceae are photolithotrophs, these processes would provide the organisms with maintenance energy during dark periods. They also explain motility of Chromatium in the dark.
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van Gemerden, H. On the ATP generation by Chromatium in darkness. Archiv. Mikrobiol. 64, 118–124 (1968). https://doi.org/10.1007/BF00406970
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DOI: https://doi.org/10.1007/BF00406970