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 end- 

 ing 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 com- 

 monly 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. 



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. 



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. 

 Family III. Achromobacteraceae, p. 296. 



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