ORDER III. HYPHOMICROBIALES DOUGLAS, Ordo Nov, 



Hy.pho.mi.cro.bi.a'les. M.L. fem.pl. n. Hyphomicrobiaceae type family of the order; 

 -ales ending to denote an order; M.L. fem.pl.n. Hyphomicrohiales the Hyphomicrobiaceae 

 order. 



Multiplication is by budding or by budding and longitudinal fission. Buds may be sessile 

 or may be borne at the tip of a slender filament which arises from the pole of a mature cell 

 or from a filament connecting two cells. Cells may occur singly or in pairs but are found more 

 commonly in aggregates. In some types the aggregates consist of groups of cells attached 

 to a surface by stalks which appear to radiate from a common holdfast; in others the ag- 

 gregates consist of free-floating cell groups in which the cells are attached to one another 

 by the filament engendered in the budding process. Branching of the filament may result 

 in groups which contain several hundred cells. Cells are ovoid, ellipsoidal, spherical or 

 pyriform. If motile, the cells possess a single polar flagellum. Specialized resting stages have 

 not been found. Gram-negative so far as known. Metabolism may be heterotrophic or 

 photosynthetic. Found in the mud and water of fresh-water ponds and streams; also para- 

 sitic on fresh-water Crustacea. 



Key to the Families of Order Hyphomicrobiales. 



I. Buds borne upon filaments. 



Family I. Hyphomicrobiaceae, p. 276. 

 II. Buds sessile. 



Family II. Pasteuriaceae, p. 278. 



FAMILY I. HYPHOMICROBIACEAE BABUDIERI, 1950. 

 (Rendiconti dell'Istituto Superiore di Sanita, 13, 1950, 589.) 



Hy.pho.mi.cro.bi.a'ce.ae. M.L. neut.n. Hyphomicrobium type genus of the family; 

 -aceae ending to denote a family; M.L. fem.pl.n. Hxjphomicrobiaceae the Hyphomicrobium 

 family. 



These organisms occur mainly as free-floating groups in which the cells are attached to 

 one another by a slender, sometimes branched, filament. Daughter-cell formation is initi- 

 ated by the outgrowth of a filament from the pole of a mature cell or from some point on a 

 filament connecting two mature cells. The daughter cell is formed by enlargement of the tip 

 of the filament. Gram-negative. 



Key to the genera of family Hyphomicrobiaceae. 



I. Chemoheterotrophic. Motile. 



Genus I. Hyphomicrobium, p. 277. 



* New material prepared by and old material rearranged by Prof. H. C. Douglas, Depart- 

 ment of Microbiology, School of Medicine, University of Washington, Seattle, Washington, 

 December, 1953. 



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