Page:Bergey's manual of determinative bacteriology.djvu/72

 in a medium rich in calcium ions, so that calcium carbonate is precipitated as the alkalinity increases, has not yet been established but seems possible. In that case the identity of this species with Rhabdomonas rosea would become evident. Source: From a pond near Graz, Austria.

Habitat: Fresh water.

Rho.do.the'′ce. Gr. noun rhodum the rose; Gr. noun thece box (capsule); Rhodothece the rose capsule.

Sulfur purple bacteria, occurring singly, not aggregated in families. Cells spherical, each surrounded by a rather wide capsule which is, however, rarely visible without special staining. Motility not observed. Contain bacteriochlorophyll and carotenoid pigments, coloring the cells reddish. Capable of photosynthesis in the presence of hydrogen sulfide; the cells then store sulfur globules, arising as an intermediate oxidation product of the sulfide.

In view of the experiences of Bavendamm and others that a number of representatives of the sulfur purple bacteria, characterized by typical colonial aggregates when found in nature, may develop as single cells in pure culture, it is quite conceivable that the genus Rhodothece is identical with some other genus, e.g., Thiopedia or Lamprocystis, and that these genera represent different growth forms induced by environmental conditions.

The type species is Rhodothece pendens Molisch.

1. Rhodothece pendens Molisch, 1907. (Die Purpurbakterien, Jena, 1907, 19.)

pen′dens. L. part. adj. pendens hanging.

Cells spherical, frequently occurring as diplococci, occasionally as very short chains or clumps of 3 to 5 individuals. 1.8 to 2.5 microns in diameter. Produce rather abundant slime. Cells embedded in individual capsules which are rarely visible without staining (India ink). Characteristic is the regular occurrence of pseudovacuoles (aerosomes) which are supposed to keep the cells suspended in liquid media. Refractive phenomena due to the pseudovacuoles and to the sulfur globules distort the cell shape under ordinary illumination so that bacteria appear as polygons rather than round cells. Usually 2 aerosomes and 2 sulfur globules per cell. Color not observable in individual bacteria. Cell groups are rose-red. Motility not observed.

Habitat: Mud and stagnant water containing hydrogen sulfide and exposed to light. Not reported from sulfur springs. Illustrations: Molisch, Die Purpurbakterien, Jena, 1907, Pl. II, fig. 13-14.

Chro.ma′ti.um. Gr. noun chromatium color, paint.

Cells occur singly, more or less ovoid, bean- or vibrio-shaped or short rods. The last-mentioned are often thick-cylindrical with rounded ends. Motile by means of polar flagella. Contain bacteriochlorophyll and carotenoid pigments, coloring the cells various shades of red. Capable of photosynthesis in the presence of hydrogen sulfide and storing elemental sulfur as an incomplete oxidation product in the form of globules inside the cells.

At present the genus contains twelve described species. Differentiation of these species has, in the past, been based almost entirely upon size and shape of individual cells, often with complete disregard for the variability of these criteria. The unsatisfactory and arbitrary nature of such a classification has occasionally been pointed out, and with much justification. Winogradsky (Schwefelbacterien, Leipzig, 1888, 98) mentions the many transitional stages that can be observed between Chromatium okenii and Chromatium weissei; Strzeszewski (Bullet. Acad. Sci., Cracovie, Sér. B, 1913, 321) holds that it is impossible to distinguish, on the basis of sizes or otherwise, between Chromatium weissei and Chromatium minus. Such contentions, derived from observations on material from natural collections or