Non-motile. Gram-negative. Colonies are salmon-pink to orange-red in color. Photohetero- trophic. Anaerobic. Found in mud and in fresh water. The type species is Rhodomicrobium vnnnielii Duchow and Douglas. 1. Rhodomicrobium vannielii Duchow and Douglas, 1949. (Duchow and Douglas, Jour. Bact., 58, 1949, 409; also see Murray and Douglas, Jour. Bact., 59, 1950, 157; and Volk and Pennington, Jour. Bact., 59, 1950, 169.) van.niel'i.i. M.L. gen. noun vannielii of van Niel; named for C. B. van Niel, an American bacteriologist. Mature cells are ovoid, measuring 1.2 by 2.8 microns; immature cells are spherical. Non-motile. The cells are connected by filaments which are approximately 0.3 mi- cron in diameter and from one to several times the length of a mature cell. A mature cell may produce as many as three daughter cells: one by formation of a primary fila- ment from the pole of the cell, and one or two more by lateral outgrowths of new fila- ments from the primary filament upon which the first daughter cell is borne. Be- cause of the tendency of the cells to remain attached to the filament, the predominant growth habit is that of an aggregate con- taining many cells. Gram-negative. Agar: In shake tubes, colonies are dark orange-red, irregular, 2 to 3 mm in diameter and have a rough, convoluted surface. Broth: Turbid in young cultures, becom- ing granular and flocculent; salmon -pink to deep orange-red, depending on the den- sity of growth. Photoheterotrophic. Cells contain bac- teriochlorophyll and carotenoid pigments. Growth occurs in the presence of light in a mineral medium containing an organic hy- drogen donor and bicarbonate; organic growth factors are not required. Suitable hydrogen donors are ethanol, propanol, butanol, acetate, propionate, butyrate, valerate, caproate, lactate and malate. Glucose, mannose, fructose, mannitol, citrate, tartrate, formate, thiosulfate and sulfide are not utilized. Anaerobic. Optimum temperature, between 25° and 30° C. Source: Isolated from mud and water from Washington State. Habitat: Commonly found in mud, pond, lake and stream waters. FAMILY II. PASTEURIACEAE LAURENT, 1890, EMEND. HENRICI AND JOHNSON, 1935. (Laurent, Compt. rend. Acad. Sci., Paris, 3, 1890, 754; Henrici and Johnson, Jour. Bact., 30, 1935, 84.) Pas.teu.ri.a'ce.ae. M.L. fem.n. Pasteuria type genus of the family; -aceae ending to denote a family; M.L. fem.pl.n. Pasteuriaceae the Pasteuria family. Stalked bacteria with spherical or pear-shaped cells; if cells are elongated, the long axis of the cell coincides with the axis of the stalk. Stalks may be very short or absent, but when present they are usually very fine and at times arranged in whorls attached to a common holdfast. Cells multiply by longitudinal fission and/or by budding. Mostly peri- phytic; one species is parasitic. The descriptions of the members of this family are largely based upon microscopic exam- inations of collected materials such as parasitized daphnias (fresh-water Crustacea) or glass slides submerged at various depths for about two weeks in Lake Alexander, Minne- sota (Henrici, Jour. Bact., 25, 1932, 277). A few crude cultures were obtained in two liquid media: one containing a mineral solution with precipitated cellulose and ammonium salts as a source of nitrogen, the other being a solution of MgS04 and K2HPO4 in tap water to
