Genus XVI Thiodictyon Winogradsky 1888 80AL Johannes F Imhoff

Thi'o.dic' ty.on. Gr. n. thios sulfur; Gr. n. dictyon a net; M.L. neut. n. Thiodictyon sulfur net.

Cells are rod shaped with rounded ends, sometimes appearing spindle-shaped, multiply by binary fission, nonmotile under all conditions, may form aggregates in which the cells are arranged end-to-end in an irregular netlike structure, the shape of which is variable. May also form clumps that are more compact or break up into individual cells. Contain large, irregularly shaped gas vesicles in the central part of the cell. Gram negative, belong to the Gammaproteobacteria, and contain internal photosynthetic membranes of vesicular type with bacteriochlorophyll a and ca-rotenoids as photosynthetic pigments.

Obligately phototrophic and strictly anaerobic. Photolithoau-totrophic growth under anoxic conditions in the light with sulfide and S0 as electron donors. During oxidation of sulfide, S0 is transiently stored in the peripheral part of the cell that is free of gas vesicles. Final oxidation product is sulfate. In the presence of sulfide and bicarbonate, simple organic substrates are pho-toassimilated.

Habitat: mud and stagnant water of ponds and lakes containing hydrogen sulfide; common as planktonic bacterium in the sulfide-containing hypolimnion of freshwater lakes.

Type species: Thiodictyon elegans Winogradsky 1888, 82.

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