ent. The sheaths become brittle and glass- like in appearance by deposition of ferric hj^droxide in a hard colloidal form. Prings- heim (Endeavour, 11, 1952, 209) states that under these conditions it is identical with Leptothrix ochracea, which looks ochre-like in bulk but never brown under the micro- scope. Source: Originally found in polluted waters. May become a real nuisance in sewage purification plants of the activated sludge type (Lackey and Wattie, op. cit., 1940, 975) and in streams polluted with sul- fite liquor from pulp and paper mills (Lackey, Mimeographed Rept., U. S. Pub. Health Ser., 1941). Habitat: Stagnant and running water, especially sewage-polluted streams. Widely distributed throughout the world in fresh water.
2. Sphaerotilus dichotomus (Cohn, 1875) Migula, 1900. (Cladothrix dichotoma Cohn, Beitr. z. Biol. d. Pflanz., 1, Heft 3, 1875, 185; Migula, Syst. d. Bakt., 2, 1900, 1033.) di.cho'to.mus. Gr. adj. dichotomus di- vided, forked. The identity of this species as distinct from Sphaerotilus natans has been ques- tioned. In his text, Cohn reports the di- ameter of the trichomes to be 0.3 micron. This clearly is an error as his figures at 600X show the diameter of the trichomes to be greater than the diameter of Bacillus anthracis spores shown at the same mag- nification. Such spores are 1.3 to 1.5 microns in diameter. Zikes (Cent. f. Bakt., II Abt., 43, 1915, 529) gives the following differential charac- ters : Cells smaller than those of Sphaerotilus natans, 1.5 to 2.5 microns; false branching constant; grows best in high concentrations of meat extract; will grow in ordinary pep- tone solutions; can utilize inorganic nitro- gen; liquefies gelatin slowly. Source: Isolated by Cohn from water con- taining Myconostoc. Habitat: Comparatively unpolluted fresh water capable of sustaining algae.
3. Sphaerotilus fluitans (Migula, 1895) Schikora, 1899. {Streptothrixfluitans Migula, in Engler and Prantl, Die natiirl. Pflanzen- fam., 1, la, 1895, 38; Schikora, Ztschr. f. Fischerei, 7, 1899, 1-28.) flu'i.tans. L. part. adj. fluitans floating. Verj thin, attached trichomes as much as 1 cm in length. The trichomes are sur- rounded by a soft sheath from which almost spherical conidia issue, usually attaching themselves to the exterior of the sheath where they multiply. Source: Found attached to pieces of wood and stems of plants in running water. Habitat: Fresh water.
Genus II. Leptothrix Kützing, 1843.
(Kützing, Phycologia Generalis, 1843, 198; not Leptotrichia Trevisan, Reale Ist. Lombardo di Sci. e Lettere, Ser. 2, 12, 1879, 138.)
Lep'to.thrix. Gr. adj. leptus fine, small; Gr. noun thrix hair; M.L. fem.n. Leptothrix fine hair.
Trichomes of cylindrical, colorless cells with a sheath at first thin and colorless, later thicker, yellow or brown, encrusted with iron or manganese oxide. The oxides may be dissolved by dilute acid, whereupon the inner cells show up well. If the sheath contains manganese oxide, it does not dissolve completel}^ in weak acids. When examined under the electron microscope, the sheath shows an alveolar structure. Multiplication is by cell division with individual cells occasionally slipping out of the sheath as reproductive cells. These are sometimes motile with a tuft of flagella. False branching may occur. Gram-negative and not acid-fast so far as known. Usually found in fresh water.
The type species is Leptothrix ochracea Kützing.
Key to the species of genus Leptothrix.
I. Trichomes straight, not spirally twisted.
- A. Trichomes free-floating and unbranched. Sheath thin.
