FAMILY I. AZOTOBACTERACEAE 285 



Distinctive characters: Tolerance of acid- because the organisms in the new genus 



ity; wide limits of pH tolerated; abundant differ in morphology and physiology in 



slime production; large globules of f;it important respects from the organisms in 



within cells. the genus Azotobacier proper. Further 



Relationships to other species: Derx comparative studies should be made before 



(Kon. Nederl. Akad. v. Wetensch., Amster- this separation is accepted, 



dam, Proc. Sect. Sci., 53, 1950, 145; Ann. Source: Isolated from soils of India and 



Bogoriensis, 1, 1950, 1) has made this species Java, 



the type species of a new genus, Beijerinckia, Habitat : Soils. 



FAMILY II. RHIZOBIACEAE CONN, 1938. 

 (Jour. Bact., 36, 1938, 321.) 



Rhi.zo.bi.a'ce.ae. M.L. neut.n. lihizobium type genus of the family; -aceae ending to 

 denote a family; M.L. fem.pl.n. Rhizohiaceae the Rhizobium family. 



Cells without endospores, rod-shaped, sparsely flagellated (one polar or lateral flagellum 

 or 2 to 4 peritrichous ones); some species are non-motile. Usually Gram-negative. One 

 genus {Chromobacterium) produces a violet pigment. Grow aerobically on ordinary culture 

 media containing glucose. Glucose and sometimes other carbohydrates are utilized without 

 appreciable acid formation. Saprophytes, symbionts and pathogens; the latter are usually 

 plant pathogens forming abnormal growths on roots and stems. 



Key to genera of family Rhizobiaceae. 



I. Cells capable of fixing free nitrogen when growing symbiotically on the roots of Legu- 

 minosae. 



Genus I. Rhizobium, p. 285. 

 II. Either plant pathogens which attack roots or produce hypertrophies on stems or free- 

 living non-chromogenic soil or water forms. Do not fix nitrogen. 



Genus II. Agrobaderiujn, p. 288. 

 III. Usually free-living soil and water forms which produce a violet chromogenesis. 



Genus III. Chromobacterium, p. 292. 



Genus I. Rhizobium Frank, 1889.* 



(Phytomyxa Schroeter, in Cohn, Kryptogamen-Flora von Schlesien, 3, 1886, 134; Frank, 

 Ber. d. deutsch. bot. Gesellsch., 7, 1889, 380.) 



Rhi.zo'bi.um. Gr. noun rhiza a root; Gr. noun bins life; M.L. neut.n. Rhizobium that 

 which lives in a root. 



Rods which measure 0.5 to 0.9 bj^ 1.2 to 3.0 microns. Motile when young, commonly chang- 

 ing to bacteroidal forms (a) upon artificial culture media containing alkaloids or glucosides, 

 or in which aciditj^ is increased, or (b) during symbiosis within the nodule. Gram-negative. 

 Aerobic. Heterotrophic, growing best with extracts of yeast, malt or other plant materials. 

 Nitrites may be produced from nitrates. Nitrites are not utilized. Gelatin is not liquefied 

 or is very slightly liquefied after long incubation. Optimum temperature, 25° C. This group 

 is capable of producing nodules on the roots of Leguminosae and of fixing free nitrogen during 

 this symbiosis. 



The type species is Rhizobium leguminosarum Frank. 



*Original revision by Dr. and Mrs. O. N. Allen, Universit}^ of Wisconsin, Madison, Wis- 

 consin, January, 1938; further revision by Dr. O. N. Allen, September, 1953. 



