606 ORDER IV. EUBACTERIALES 



regard Arthrohacler Fischer (Jahrb. f. vvissen. Bot., 27, 1895, 141) as a nomen dubiurn, no 

 species having been named as belonging to the genus by Fischer. Under these circumstances 

 Arthrohacler Fischer would appear to be illegitimate. Conn and Dimmick (op. cil., 1947, 

 300) revived Fischer's name for the organisms they describe as they feel it to be an ap- 

 propriate name. Fischer defined Arthrohacler as including all non-flagellate, rod-shaped 

 bacteria which produce "arthrospores" as recognized by De Bary. While the real meaning 

 of arthrospores is somewhat uncertain, it sometimes has been used for the coccoid bodies 

 developed by the species placed in Arthrohacler as defined here. 



In young cultures the cells appear as rods which may vary in size and shape from straight 

 to bent, curved, swollen or club-shaped forms; snapping division may show angular cell 

 arrangement. Short filament formation with rudimentary budding may occur, especially 

 in richer liquid media. Gram-negative or Gram-variable. Coccoid cells are characteristically 

 observed in cultures after one or more days; these coccoid cells persist as the predominant 

 form in older cultures and are Gram-negative to Gram-positive. Larger coccoid cells (cys- 

 tites), which give rise to one or more rod-shaped cells on fresh transfer, also occur. Gen- 

 erally non-motile. Growth on solid media soft or viscous; growth in liquid media generally 

 not profuse. Most species liquefy gelatin. Little or no acid from carbohydrates. Nitrites 

 generally produced from nitrates. Indole not produced. Aerobic. Most species show little or 

 no growth at 37°C. Typically soil organisms. 



The type species is Arthrohacler glohifonnis (Conn) Conn and Dimmick. 



Key to the species of genus Arthrobacter. 



I. Utilize nitrates or ammonium salts as a sole source of nitrogen; utilize citrate as a sole 

 organic nutrient. 



A. Non-chromogenic. 



1. Starch hydrolyzed; little or no growth at 37° C. 



a. Growth not viscous in liquid or on solid media; moderate growth on aspara- 

 gine agar. 



1. Arthrohacter glohiformis. 



aa. Growth viscous in most liquid or solid media; profuse growth on asparagine 

 agar. 



2. Arthrohacler pascens. 



2. Starch not hydrolyzed; grows well at 37° C. 



3. Arthrohacter simplex. 



B. Chromogenic. 



1. Starch h3'drolyzed; nitrites produced from nitrates. 



a. Grows profusely on nicotine agar producing a diffusible blue pigment; some 

 strains produce yellow pigment on plain agar. 



4. Arthrobacter oxydans. 



aa. Poor growth on nicotine agar, and no blue pigment is produced; yellow pig- 

 ment on plain agar. 



5. Arthrohacler aurescens. 



2. Starch not hydrolyzed; nitrites not produced from nitrates; yellow pigment on 

 plain agar. 



6. Arthrobacter ureafaciens. 



II. Do not utilize nitrates or ammonium salts as a sole source of nitrogen; citrates not 

 utilized. 



A. Non-chromogenic; weak diastatic action; agar colonies punctiform. 



7. Arthrobacter lumescens. 



B. Chromogenic; no diastatic action; agar colonies 1 to 2 mm in diameter. 



1. Yellow pigment produced on plain agar; gelatin liquefied; grows at 10° C. 



8. Arthrohacter citreus. 



