Taxonomic Comments

The temperature range for growth of Thermochromatium tepidum restricts development of this bacterium to hot springs and other thermal environments with sulfide and light (Madigan, 1984; Castenholz and Pierson, 1995). The successful adaptation to growth at high temperatures was regarded as a taxonomically relevant property of Thermochromatium tepidum, which is also phy-logenetically distinct from mesophilic freshwater Chromatiaceae species. Therefore, Chromatium tepidum was transferred to the new genus Thermochromatium (Imhoff et al., 1998b).

Further Reading

Imhoff, J.F., Suling, J. and Petri, R. 1998. Phylogenetic relationships among the Chromatiaceae, their taxonomic reclassification and description of the new genera Allochromatium, Halochromatium, Isochro-matium, Marichromatium, Thiococcus, Thiohalocapsa, and Thermochromatium. Int. J. Syst. Bacteriol. 48: 1129-1143. Madigan, M.T. 1986. Chromatium tepidum sp. nov., a thermophilic photosynthetic bacterium of the family Chromatiaceae. Int. J. Syst. Bacteriol. 36: 222-227.

List of species of the

1. Thermochromatium tepidum (Madigan 1986) Imhoff, Suling and Petri 1998b, 1140VP (Chromatium tepidum Madigan 1986, 226.)

te'pi.dum. L. neut. adj. tepidum lukewarm.

Cells are rod shaped, 1-2 X 2.8-3.2 |m, occasionally motile by flagella. Photosynthetic pigments are bacterio-chlorophyll a, esterified with phytol, and carotenoids of the normal spirilloxanthin group, with rhodovibrin and spiril-loxanthin as predominant components.

Strictly anaerobic and obligately phototrophic. Growth occurs photolithoautotrophically in mineral media supplemented with sulfide as electron donor. Hydrogen and thi-osulfate not utilized as electron donors. Acetate and py-ruvate photoassimilated in the presence of sulfide. Citric

Thermochromatium acid cycle intermediates, other than acetate, fatty acids, and sugars not utilized. Ammonia, urea, and glutamine serve as nitrogen sources. No growth factors required. Poly-b-hy-droxybutyrate is a storage material.

Thermophilic freshwater bacterium with optimum growth at 48-50°C, no growth below 34°C or above 57°C. Optimum pH is 7.0. NaCl is not required for growth and is inhibitory at concentrations above 1% (w/v).

Habitat: Sulfide-containing hot springs of neutral to alkaline pH at temperatures from 35 to 60°C. The mol% G + C of the DNA is: 61.5 (Tm). Type strain: MC, ATCC 43061, DSM 3771. GenBank accession number (16S rRNA): M59150.

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