[Cir. 130— B] 



THE USE OF CONGO RED IN CULTURE MEDIA.^ 



By Karl F. Keixerman, Physiologist in Charge of 8oH-Bacteriologij and Plant- 

 Nutrition Investigationfi. 



INTRODUCTION. 



In an earlier publication - mention was made of the value of 

 a medium colored with congo red as a presumptive identifica- 

 tion of the organism Bacilhis tumefacieTis, which is the cause of 

 crown-gall of orchard trees, vines, etc., and which also produces 

 tumors upon the roots of tomatoes, sugar beets, carrots, clover, alfalfa, 

 and other plants. Certain strains of Bacillus tumefaciens if grown 

 upon a suitable nutrient agar distinctly colored with congo red 

 absorb the dye, thus staining the bacterial growth a vivid red and 

 at the same time bleaching the layer of the culture medium. The 

 absorption of the congo-red dye from the medium by the growing 

 colony is usually such a decisive and striking action with many 

 strains of Bacillus tumefaciens that it seemed desirable to test the 

 diagnostic value of congo-red media for the common saproj^hytic 

 bacteria. 



DESCRIPTION OF TESTS OF CULTURES. 



Through the courtesy of Prof. C.-E. A. Winslow 28 species of 

 bacteria were secured from the American Museum of Natural His- 

 tory, and these, together with two strains of Bacillus tumefaciens^ 

 were plated out in Petri dishes in quadruplicate and were also grown 

 in stab culture in various media. The fact that there had been 

 recently isolated new species of bacteria ^ which destroy cellulose 

 and which are also able to grow luxuriantly upon the usual standard 

 culture media, such as beef agar, beef gelatin, and milk, has sug- 

 gested the possibility that many of the common saprophytic bacteria 

 described by various authors might have the power of dissolving 

 cellulose. Although the determination of a cellulose-dissolving func- 

 tion has no connection whatever with the diajniostic value of consfo- 

 red media, for mechanical reasons it has been convenient to study 

 simultaneously the action of various species of bacteria upon cel- 

 lulose media as well as upon congo-red media. 



1 Issued June 21, 1913. 



2 Kellerman, Karl F. The relation of crown-gall to legume inoculation. U. S. Depart- 

 ment of Agriculture, Bureau of Plant Industry, Circular 76, 6 p., 1 pi., 1911. 



= Kellerman, Karl F.. and McBeth, I. G. The fermentation of cellulose. Centralblatt 

 fxir Bakteriologie [etc.], Abt. 2, Bd. 34, No. 18/22, pp. 48.5-494, 2 pi., 1912. 



McBeth, I. G., and Scales, F. M. The destruction of cellulose by bacteria and fila- 

 mentous fungi. U. S. Department of Agriculture, Bureau of Plant Industry, Bulletin 

 266, 50 p., 4 pi., 1913. 



[Cir. 130] 15 



