Key to the genera of familij Spirochaetaceae. I. No obvious periplast membrane and no cross striations present. Genus I. Spirochaeta, p. 893. II. Periplast membrane present. Cross striations present in stained specimens. A. Free-living in marine ooze. Genus II. Sapros-pira, p. 894. B. Parasitic on lamellibranch molluscs. Cristae are prominent. Genus III. Cristispira, p. 895. Genus I. Spirochaeta Ehrenberg, 1833. (Ehrenberg, Abhandl. Berl. Akad., 1833, 313; Spirochoeia Dujardin, Hist. nat. des Zoophytes infusoires, Paris, 1841, 209; Spirochaete Cohn, Beitr. z. Biol. d. Pflanz., 1, Heft 1, 1872, 180.) Spi.ro. chae'ta. Gr. noun spira a coil, spiral; Gr. noun chaete hair; M.L. fem.n. Spiro- chaeta spiral hair. Flexible, undulating, spiral-shaped rods with or without flagelliform, tapering ends. The protoplast is wound spirally around a well defined axial filament; there is no obvious periplast membrane and there are no cross striations. The primary spiral is permanent. Motility is by a creeping motion along the surface of supporting objects. Presumably Gram- negative. Non-parasitic. Found free-living in fresh- or sea-water slime, especially in the presence of hydrogen sulfide; common in sewage and foul waters. The type species is Spirochaeta plicatilis Ehrenberg. Key to the species of genus Spirochaeta. I. Large spirals with rounded ends. 1. Spirochaeta plicatilis. 2. Spirochaeta marina. 3. Spirochaeta eurystrepta. II. Smaller spirals with pointed ends. 4. Spirochaeta stenostrepta. 5. Spirochaeta daxensis. 1. Spirochaeta plicatilis Ehrenberg, 1838. (Die Infusionstierchen, 1838, 83.) pli.ca'ti.lis. L. adj. plicatilis flexible. Cylindrical, spiral-shaped rods, 0.5 to 0.75 by 100 to 500 microns, with blunt ends. There are several, large, inconstant, irregu- lar waves. Spiral amplitude: 2.0 microns, regular; spiral depth: 1.5 microns, regular. A flexible, elastic, axial filament, consisting of chitin or of a cutin-like substance, is distinct in stained specimens; this filament is resistant to trypsin digestion. Multiplica- tion is by transverse fission. Stain violet with Giemsa's stain and gray with iron- hemotoxylin. Cytoplasmic spirals stain with eosin, rubin, etc. Cells contain volutin granules and fat inclusions. Gram-negative (Dyar, Jour. Bact., 54, 1947, 490). Dyar (ibid., 483), who used recent micro- scopic and staining techniques in her stud- ies, questions the presence of axial filaments and the absence of distinct periplast mem- branes and of prominent cross striations in this species. Although not cultivable on ordinary lab- oratory media, Dyar (ibid., 483) succeeded in obtaining good growth of pure cultures on a blood-enriched agar medium which contained a dilute decoction of decaying leaves from a hydrogen sulfide spring; the hydrogen sulfide was found to be apparently unnecessary for growth. Bile salts (10 per cent) : Cells become shadowy and pale but do not dissolve. Saponin (10 per cent): Cells live for 30 minutes; later they become shadowy but do not dissolve. Grows best under low o.xygen tension.
