34. Arthrobacter 



One culture labeled Arthrobacter citreus was received from 

 Dr. L. E. Sacks of U.S.D.A., Albany, California (Fig. 36). The 

 culture grew well on simple media with a lemon yellow, water 

 insoluble pigment. The organism was gram positive, very pleo- 

 morphic and showed some motility in moist preparation. The 

 motility was nonprogressive and consisted mainly of spinning and 

 wiggling. 



Flagellar Characteristics 

 The one culture of A. citreus examined showed mainh' straight 

 flagella (or very small amplitude flagella) with nonpolar or peri- 

 trichous arrangement. Most individuals showed only one flagel- 

 lum. One organism only was seen with a normal flagellum. How- 

 ever, reports in the literature show Arthrobacter simplex with both 

 normal (wavelength about 2 microns) and curly (wavelength 

 about 1 micron ) flagella so the strain of A. citreus studied may not 

 have had the most typical flagellation of the genus. 



3 5 . Listeria 



All strains of Listeria are classified into the one species Listeria 

 monocytogenes. The organism is peritrichously flagellated, and 

 well flagellated if cultured at low temperatures such as 20° C, but 

 very poorly flagellated if cultured at 37° C. At 38° C. flagella are 

 not produced. In cultures at 37° C. a single flagellum may be 

 found on a small proportion of the organisms which led to the 

 early reports that the organism was polar monotrichous. 



Of all the bacteria the author has encountered Listeria has 

 shown the greatest genetic instability, or mutability, in regard to 

 flagellar shape and function (see Fig. 37). This apparent mutabil- 

 ity may partly be due to the fact that a large number of strains 

 (eighty-one) were studied, since a large proportion (85%) of 

 the strains did not show any variants. The cultures were all old 

 stock strains and this in itself appears to contribute to genetic 

 instability. All of the cultures included in this study were received 

 from Dr. A. M. Griffin of George Washington University. 



Flagellar Characteristics 

 The flagella of Listeria showed four distinct shapes: normal, 

 small ampfitude, straight, and coiled. Variants with each type of 

 flagella were isolated in pure culture. Curiously enough the var- 



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