ORDER IV. EUBACTERIALES BUCHANAN, 1917.
(Jour. Bact., 2, 1917, 102.)
Eu.bac.te.ri.a'les. Gr. pref. eu- well, true; Gr. neut.n. hacterium a small rod; -ales ending to denote an order; M.L. fem.pl.n. Euhacteriales the order of the true bacteria.
Simple, undifferentiated, rigid cells which are either spherical or straight rods. In some families, for e.xample Corynehacteriaceae, a certain amount of pleomorphism occurs. Only the simplest forms of branching occur, and these only rarely. There are many non-motile as well as motile species. The flagella are usually arranged peritrichously, but monotrichous species do occur in groups where the flagellation is normally peritrichous; such conditions appear to have been developed from ancestral peritrichous species. Tj'pical endospores occur in one family (Bacillaceae) . All of the species in certain families are definitely Gram-negative; in other families and groups, where the majority of species are Gram-positive, at least in certain stages of growth, species occur which lose their Gram stain so readily that they are generally classed as Gram-negative. Reproduction is by transverse fission; occasionally the cells divide in two or three planes perpendicular to each other, thereby forming tetrads or packets of eight cells. The pigments of chromogenic species are commonly non-water-soluble and of a carotenoid nature; other pigments do occur however, some of which show slight powers of diffusion into agar media. None of these pigments have the ability to carry out photosynthesis. The order includes saprophytes, parasites and many pathogenic species; the latter cause diseases of both animals and plants. Found in salt and fxesh waters, air, soil and in the bodies of animals and plants.
Key to the families of order Euhacteriales.
- I. Cells rod-shaped (rarely large, yeast-like cells). Gram-negative.
- A. Aerobic or facultatively anaerobic.
- 1. Large ovoid to rod-shaped cells which may be yeast-like in appearance. Free-living in soil. Fix free nitrogen.
- A. Aerobic or facultatively anaerobic.
Family I. Azofobacteraceae, p. 283.
- 2. Not as above.
- a. Heterotrophic rods which may not require organic nitrogen for growth. Usually motile by means of one to six flagella. Frequently form nodules or tubercles on roots of plants or show violet chromogenesis. Colonies usually large and slimy, especially on mannitol agar.
- 2. Not as above.
Family II. RMzobiaceae, p. 285.
- aa. Not as above.
- b. Straight rods which grow readily on ordinary peptone media. May or may not ferment sugars anaerobically with the production of organic acids.
- c. Glucose usually attacked oxidatively or not at all. Only rarely are species able to ferment glucose anaerobically. Produce little or no acid in litmus milk. May or may not reduce nitrates. Many yellow chromogens. Some species digest agar, others chitin. Primarily found as saprophytes in foods, in soil and in fresh and salt water.
- b. Straight rods which grow readily on ordinary peptone media. May or may not ferment sugars anaerobically with the production of organic acids.
- aa. Not as above.
Family III. Achromobacteraceae, p. 296.
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