Taxonomic Comments

The trend towards the use of 16S rDNA sequences in the taxonomy of anoxygenic phototrophic bacteria has indicated that many genera, such as Chromatium, Thiocapsa, and Amoebobacter, which are phenotypically relatively heterogeneous are also phy-logenetically heterogeneous. However, this has also led to a tendency to rely heavily on the 16S rDNA sequences and to reduce many phenotypic parameters to being "unreliable". 16S rDNA sequence analysis of the type strain of Pfennigia purpurea (DSM 4197) indicates that this strain has a high degree of sequence similarity to Lamprocystis roseopersicina DSM 229. However, two 16S rDNA sequences have been deposited as AJ223235 and Y12366, both being from the type strain of Pfennigia purpurea DSM 4197, although they are sufficiently different to infer that they come from different species. Thus, while Pfennigia purpurea (DSM 4197;

Oval to spherical cells, 1.9-3.8 X 2.0-4.5 lm. May form large aggregates (up to 40 cells). Gas vacuoles occur in the central part of the cytoplasm. The intracytoplasmic membrane system is of the vesicular type. Nonmotile. Gram negative. Photolitho-trophic under anaerobic conditions in the light; chemoautotro-phic under microaerobic conditions in the dark. Hydrogen sulfide, thiosulfate, and S0 serve as electron donors. Globules of S0 appear in cells during oxidation of sulfide or thiosulfate to sulfate. Major photosynthetic pigments are bacteriochlorophyll a and the carotenoid okenone. Isolated from the chemocline of freshwater lakes.

Type species: Pfennigia purpurea (Eichler and Pfennig 1988)

*Editorial Note: The type species of Pfennigia, P. purpurea, has been transferred to the genus Lamprocystis as L. purpurea (Eichler and Pfennig 1988) Imhoff 2001b comb. nov.

GenBank accession no. AJ223235) shows less than 1% 16S rDNA sequence divergence from Lamprocystis roseopersicina (DSM 229; GenBank accession no. AJ006063), the degree of sequence divergence between the latter and Pfennigia purpurea (DSM 4197; GenBank accession no. Y12366) may be more than 3%. In the first case, it would be appropriate to examine the possibility that Pfennigia purpurea (DSM 4197; Y12366) and Lamprocystis roseoper-sicina (DSM 229; AJ006063) are members of the same species, whereas in the latter case their membership in the same genus is questionable. These two possibilities cannot be decided based on currently available sequence data. It should be pointed out that it is implicit in the evaluations of Guyoneaud et al. (1998b), Imhoff et al. (1998b), or Puchkova et al. (2000) that species sharing 5% or less 16S rDNA sequence divergence belong in the same genus. However, this is usually without adequate supporting data or in the light of other phenotypic data being "unreliable". In other genera, sequence similarities may be higher than 95% and rely on supporting phenotypic data (see, for example, Lincoln et al., 1999).

List of species of the genus Pfennigia

1. Pfennigia purpurea (Eichler and Pfennig 1988) Tindall 1999, 1308VP (Amoebobacter purpureus Eichler and Pfennig 1988, 399.)

pur.pui1 ea. L. fem. adj. purpurea purple or purple-red.

The characteristics are as given for the genus. The mol%o G + C of the DNA ts: 63.4-64.1 Type strain: ThSch12, DSM 4197.

GenBank accession number (16S rRNA): AJ223235, Y12366.

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