SUling 1996 112

Johannes F. Imhoff

Ha'io.rho'do.spi'ra. Gr. gen. n. halos of the salt; Gr. n. rhodon the rose; Gr. n. spira the spiral; M.L. fem. n. Halorhodospira the spiral rose from salt lakes.

Cells spirals or rods, 0.5-1.2 |m in diameter, motile by means of bipolar flagella, multiply by binary fission. Gram negative and belong to the Gammaproteobacteria. Internal photosynthetic membranes appear as lamellar stacks that are continuous with the cytoplasmic membrane. Photosynthetic pigments are bacterio-chlorophyll a or b and carotenoids.

Grow photoautotrophically under anoxic conditions with reduced sulfur compounds as electron donors, or photohetero-trophically with a limited number of simple organic compounds. Sulfide oxidized to S0, which is deposited outside the cells and may be further oxidized to sulfate.

Growth dependent on highly saline and alkaline conditions. Greater than 10% (w/v) total salt concentration required by all known species, some of which grow in saturated salt solutions.

Glycine betaine, ectoine, and trehalose accumulated as compatible solutes in response to salt and osmotic stress. Growth factors not required. Storage products are polysaccharides, poly-b-hy-droxybutyrate, and polyphosphate.

Halorhodospira species are found in hypersaline and extremely saline environments with slightly to extremely alkaline pH (up to pH 11-12) that contain sulfide and are exposed to light, such as salt flats, salt lakes, and soda lakes.

Type species: Halorhodospira halophila (Raymond and Sistrom 1969) Imhoffand Suling 1997, 915 (Effective publication: Imhoff and Suling 1996, 110) (Ectothiorhodospira halophila Raymond and Sistrom 1969, 125.)

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