Genus XV Thiocystis Winogradsky 1888 60aL emend Imhoff Suling and Petri 1998b 1138

Johannes F. Imhoff

Thi.o.cys'tis. Gr. n. thios sulfur; Gr. n. cystis the bladder, a bag; M.L. fem. n. Thiocystis sulfur bag.

Cells are rod shaped or ovoid to spherical, before cell division often diplococcus-shaped, motile by flagella, occurring singly or in pairs; may grow in irregular aggregates surrounded by slime, multiply by binary fission. Gram negative, belong to the Gam-maproteobacteria, and contain internal photosynthetic membranes of vesicular type in which the photosynthetic pigments bacterio-chlorophyll a and carotenoids are located.

Photolithotrophic growth occurs under anoxic conditions in the light with sulfide and S0 as electron donors. Thiosulfate and hydrogen may also be used. During oxidation of sulfide, S0 is transiently stored inside the cells in the form of highly refractile globules. Sulfate is the final oxidation product. In the presence of sulfide and bicarbonate, simple organic substrates can be pho-toassimilated. Some species grow chemoautotrophically or che-moorganotrophically under microoxic to oxic conditions in the dark. Storage materials: polysaccharides, poly-b-hydroxybutyrate, S0, and polyphosphates.

Ubiquitous, mesophilic bacteria with optimum growth at 25-35°C and pH 6.5-7.6, that can be isolated from freshwater, brackish water, and marine environments.

Habitat: anoxic sulfide-containing water and mud of fresh water ponds and lakes, as well as brackish water and marine environments exposed to light.

Type species : Thiocystis violacea Winogradsky 1888, 65.

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