FAMILY I. CHLAMYDOBACTERIACEAE 263 



Genus I. Sphaerotilus, p. 263. 

 II. Trichomes surrounded by sheaths impregnated with oxides of iron or manganese which 

 dissolve in strong h.ydrochloric acid. Free-living or sessile. 



A. Individual trichomes, each with a sheath. 



Genus II. Leptothrix, p. 264. 



B. Sheaths contain more than one trichome; the trichomes are sometimes in a fan-like 

 arrangement. 



Genus III. Toxothrix, p. 269. 



Genus I. Sphaerotilus Kiitzing, 1833. 



(Kiitzing, Linnaea, 8, 1833, 385; Cladothrix Cohn, Beitr. z. Biol. d. 

 Pflanz., 1, Hefts, 1875, 185.) 



Sphae.ro'ti.lus. Gr. noun sphaera a sphere; Gr. noun tilus anything shredded, flock, 

 down; M.L. mas.n. Sphaerotilus sphere down. 



Attached or free-floating, colorless trichomes showing false branching, though this may 

 be rare in some species. When e.xamined under the electron microscope, the sheath shows a 

 homogeneous structure. Sheath may become j'ellowish or brown with the deposition of iron 

 oxide. The deposition of iron is dependent on environmental factors, not on the ph3'siologi- 

 cal ability to store iron. Trichomes consist of rod-shaped or ellipsoidal cells surrounded by 

 a firm sheath. Multiplication occurs both by non-motile conidia and by motile swarm cells, 

 the latter with a subpolar tuft of flagella. Gram-negative so far as known. Found in fresh 

 water. 



The systematic positions of the species placed in Sphaerotilus, Leptothrix and related ge- 

 nera are uncertain. Pringsheim (Phil. Trans. Roy. Soc. London, Series B, 233, 1949, 605, 

 and Biol. Reviews, 24, 1949, 200) would combine some of the species now placed in Lepto- 

 thrix with Sphaerotilus nutans and broaden the definition of Sphaerotilus to include other 

 species here placed in Leptothrix and Clonothrix. However, Beger and Bringmann (Zent. f. 

 Bakt., II Abt., 107, 1953, 318) indicate differences in the structures of the sheaths of Sphaero- 

 tilus and Leptothrix and give other reasons why it may be better to keep the earlier groupings 

 as they have been. 



The type species is Sphaerotilus natui^s Kiitzing. 



1. Sphaerotilus natans Kiitzing, 1833. nitrogen, does not grow in the ordinary pep- 



(Kiitzing, Linnaea, 8, 1833, 385; not (Sp/jae?o- tone solution, grows best with low concen- 



tilus natans Sack, Cent. f. Bakt., II Abt., trations of meat extract (Zikes, Cent. f. 



65, 1925, 116.) Bakt., II Abt., 4S, 1915, 529). See Stokes 



na'tans. L. part. adj. wafa/is swimming. (Jour. Bact., 67, 1954, 278) for a recent study 



Colorless, slimy trichomes which attain of the cultural and physiological charac- 



a length of several millimeters. The tri- teristics of this species, 



chomes are ensheathed, show false branching Distinctive characters: This species 



and are either free-floating or attached at thrives in great tassels on solid substrata 



one end by means of a small disc. The indi- covered by dirty running water. These tas- 



vidual cells are cylindrical, 1 by 2 to 6 mi- sels are composed of trichomes of bacterial 



crons, and vacuolated (Lackey and Wattie, cells held together by slim}^, tubular 



U. S. Pub. Health Ser., Pub. Health Repts., sheaths. The latter maj' become softened 



55,1940,975). and dissolved, releasing Pseudomonas-hke 



]\Iultiplication occurs through the forma- swarm cells. The same organism grows in 



tion of conidia within the sheath of the a quite different state in quiet waters 



vegetative cells, from which thej' swarm out with only a little organic matter, forming 



at one end, swim about for a time, then branched structures occurring in trichomes, 



attach themselves to objects and develop the sheaths of which are not slimy. A third 



into delicate trichomes. form is produced when ferrous compounds 



Gelatin rapidly liquefied, requires organic and very little organic substance are pres- 



