Taxonomic Comments

Purple sulfur bacteria having the morphology first described by Winogradsky for Thiopedia rosea are widely distributed in sulfide-containing ponds and lakes (Utermohl, 1925; Eichler and Pfennig, 1991). Fine-structure studies of Thiopedia-like cell material collected from a purple bacteria bloom in a small forest pond (Michigan, USA) revealed the presence of at least two cell types with different internal membrane systems (Hirsch, 1973). One type contained a vesicular membrane system, while the other type contained a membrane system that consisted of stacks of disk-shaped lamellae. Thin section micrographs of the type strain of Thiopedia rosea, showing a vesicular membrane system, were published by Remsen (1978).

The description of T. rosea given here is based on information from five strains described by Eichler and Pfennig (1991). Little information on this species was previously available. It should be noted, however, that the properties of the five isolates differ in some aspects from earlier descriptions. Winogradsky (1888) indicated a cell diameter of 1-2 |m and Pfennig (1989c) reported cells being 1.2-1.6 X 1.5-2.0 |m and requiring vitamin B12. The latter property was not substantiated by Eichler and Pfennig (1991) and cells were reported to be 2.0-2.5 X 2.5-3.0 |m by these authors.

Unfortunately, the ability of Thiopedia to multiply in rectangular platelets, as characteristically observed in many natural habitats, is gradually lost over periods of months or years in pure culture. Therefore, it is not a taxonomically reliable character. Because the formation of rectangular platelets was considered a genus-specific property, distinguishing Thiopedia from other Chro-matiaceae species (Pfennig and Traper, 1989), recognition of the taxonomic unreliability of this property raises questions about the existence of the genus Thiopedia. Further studies are needed to show whether Thiopedia rosea is a close relative of Thiolampro-vum pedioforme, which also forms rectangular platelets (Eichler and Pfennig, 1986), or Thiocapsa species, that do not form large platelets, but may form tetrads of cells.

Further Reading

Eichler, B. and Pfennig, N. 1986. Characterization of a new platelet-forming purple sulfur bacterium, Amoebobacter pedioformis sp. nov. Arch. Microbiol. 146: 295-300. Eichler, B. and Pfennig, N. 1991. Isolation and characteristics of Thiopedia rosea (neotype). Arch. Microbiol. 155: 210-216. Hirsch, P. 1973. Fine structure of Thiopedia spp. In Drews (Editor), Abstracts of the Symposium on Prokaryotic Photosynthetic Organisms, Freiburg. p. 184-185. Pfennig, N. 1973. Culture and ecology of Thiopedia rosea. In Drews (Editor), Abstracts of the Symposium on Prokaryotic Photosynthetic Organisms, Freiburg. p. 75-76. Remsen, C.C. 1978. Comparative subcellular architecture of photosyn-thetic bacteria. In Clayton and Sistrom (Editors), The Photosynthetic Bacteria, Plenum Press, New York. p. 31-60. Utermohl, H. 1925. Limnologische Phytoplanktonstudien. Arch. Hydro-biol. Suppl. 5: 251-277.

List of species of the genus Thiopedia

1. Thiopedia rosea Winogradsky 1888, 85AL ro'se.a. L. adj. rosea rose-colored, pink.

Cells spherical to ovoid, 2.0-2.5 X 2.5-3.0 |im, with regular arrangements in rectangular platelets of up to 64 or more cells (Fig. BXII.y.16). Nonmotile and contain gas vesicles in the central part of the cells. Individual cells colorless, color of cell suspensions bright purple-red. Internal pho-tosynthetic membranes of vesicular type. Photosynthetic pigments are bacteriochlorophyll a and carotenoids with okenone as major component.

Obligately phototrophic and strictly anaerobic. Photo-lithoautotrophic growth with sulfide and S0 as electron donors. Sulfide concentrations above 0.6 mM are growth inhibitory. In the presence of sulfide and bicarbonate, the following substrates are photoassimilated: acetate, pyruvate, butyrate, valerate (not more than 0.03% (w/v) of each to be added), and glucose. Some strains also utilize succinate, fumarate, malate, and fructose (0.05%). Ammonium salts serve as nitrogen source. Reduced sulfur compounds required as sulfur source. Assimilatory sulfate reduction does not occur. Growth enhanced by the addition of 100 |M dithionite to growth media.

Mesophilic planktonic freshwater bacterium with optimum growth at 23°C and pH 7.3-7.5.

Habitat: anoxic and sulfidic water of stratified freshwater lakes.

Type strain: 4711, DSM 1236 (neotype strain; no type strain available).

FIGURE BXII.y.16. Thiopedia rosea strain 4211 cultured photoautotroph-ically with sulfide and acetate. The light areas inside the cells are the gas vacuoles. In some of the platelets, synchronously dividing cells can be recognized. Phase-contrast micrograph. Bar = 10 |m.
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