Purple sulfur bacteria were observed in warm thermal
springs as early as 1897 (13). From recent surveys of
photosynthetic procaryotes that inhabit thermal springs it is
clear that purple bacteria which resemble Chromatium are
present at temperatures between 40 and 60"C, especially in
springs containing significant levels of hydrogen sulfide
(1-3). The first pure culture of a purple bacterium capable of
growth at temperatures above 50°C was obtained by me and
was identified as a Chromatium species by its rod-shaped
morphology, assemblage of pigments, and ability to oxidize
sulfide and store elemental sulfur intracellularly (8). Because
the characteristics of this organism are unique among pub-
lished descriptions of purple sulfur bacteria (family
Chromatiaceae), the new organism is more thoroughly char-
acterized in this paper and is described as a new species