Taxonomic note: transfer of Amoebobacter purpureus to the genus Pfennigia gen. nov., as Pfennigia purpurea comb. nov., on the basis of the illegitimate proposal to make Amoebobacter purpureus the type species of the genus Amoebobacter

This taxonomic note addresses a nomenclatural problem created by Guyoneaud et al. (1998) during reclassification of sulfur bacteria. When Amoebobacter roseus (the original type species of genus Amoebobacter) was transferred to genus Thiocapsa, the authors illegitimately proposed elevating Amoebobacter purpureus to type species of the remaining genus Amoebobacter. According to the Bacteriological Code, type species cannot be arbitrarily changed—the type is permanently associated with a genus name. This proposal violated Rule 23a(ii) and is therefore illegitimate. To resolve this conflict while acknowledging that A. purpureus warrants separate classification from the reclassified species, Tindall proposes transferring Amoebobacter purpureus to a new genus Pfennigia gen. nov., creating the combination Pfennigia purpurea comb. nov. The organism is a Gram-negative, photolithotrophic purple sulfur bacterium that uses sulfide, thiosulfate, or elemental sulfur as electron donors, with bacteriochlorophyll a as its major photosynthetic pigment. It belongs to the Thiocapsa–Thiolamprovum phyletic group within Proteobacteria gamma-subclass with 63.4–64.1 mol% G+C DNA content.

Key findings

• Guyoneaud et al.'s proposal to make Amoebobacter purpureus the type species of genus Amoebobacter violates the Bacteriological Code, as type species cannot be arbitrarily designated
• Amoebobacter purpureus is transferred to the new genus Pfennigia as Pfennigia purpurea comb. nov.
• Pfennigia purpurea is a photolithotrophic purple sulfur bacterium with vesicular photosynthetic membranes and bacteriochlorophyll a
• The organism belongs to the Thiocapsa–Thiolamprovum phyletic group within the gamma-subclass Proteobacteria