Differentiation of the species of the genus Chromatium

The most significant known difference between C. okenii and C. weissei is the cell width (Table BXII.y.4 of the chapter describing the family Chromatiaceae).

List of species of the genus Chromatium

1. Chromatium okenii (Ehrenberg 1838) Perty 1852, 174AL (Monas okenii Ehrenberg 1838, 15.)

o.ken'i.i. M.L. gen. n. okenii of Oken, named for L. Oken, a German naturalist.

Cells straight or slightly curved rods, 4.5-6.0 X 8-16 |im, occasionally longer, motile by a polar tuft of flagella which is 1.5-2 times the cell length and visible by brightfield (Fig. BXII.y.5) or phase-contrast microscopy. In the pres-

ence of sulfide and light, globules of elemental sulfur appear evenly distributed within the cell. Color of individual cells and of cell suspensions is purple-red. Photosynthetic pigments are bacteriochlorophyll a and the carotenoid oke-none.

Strictly anaerobic and obligately phototrophic. Sulfide-reduced media required. Sulfide and S0 used as photosyn-thetic electron donors. In the presence of sulfide and bi-

carbonate, acetate and pyruvate are photoassimilated. Not utilized: thiosulfate, molecular hydrogen, sugars, sugar alcohols, alcohols, higher fatty acids, amino acids, benzoate, formate, and most intermediates of the tricarboxylic acid cycle. Assimilatory sulfate reduction is absent. Nitrogen sources: ammonium salts, and urea. Vitamin B12 required.

Mesophilic freshwater bacterium with optimum growth at 20-35°C and pH 7.0 (range 6.5-7.3).

Habitat: water and sediment surface layers of stagnant freshwater habitats such as ditches, ponds, and lakes, containing hydrogen sulfide and exposed to light.

Type strain: 1111, BN 6010, DSM 169.

GenBank accession number (16S rRNA): AJ223234, Y12376.

2. Chromatium weissei Perty 1852, 174AL

weis'se.i. M.L. gen. n. weissei ofWeisse, named forJ.F. Weisse, a German zoologist.

Cells are rod shaped, 3.5-4.5 X 7-14 |im. Nitrogenase activity is present. Other characteristics are as for C. okenii.

Type strain: DSM 171.

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