FAMILY II. RHIZOBIACEAE 293 



lost (Sneath, Jour. Gen. Microbiol., 13, 1955, p. I, has recently reported that these organ- 

 isms are highly sensitive to traces of hydrogen peroxide in the medium). They have a ten- 

 dency to produce mucous, gummy, gelatinous or even leather^' growths (Corpe, Jour. Bact., 

 65,1953,470). 



The separation of the true violet chromogens into three species is in accord with the 

 recommendations of Cruess-Callaghan and Gorman (Sci. Proc. Royal Dublin Soc, 21, 

 1938, 213). Their conclusions were based on a study of 18 named cultures from culture col- 

 lections and 6 freshly isolated cultures. Others have studied this same problem. For ex- 

 ample, Hans and Bicknell (Bact. Proc. 53rd Gen. Meeting Soc. Amer. Bact., San Francisco, 

 1953, 33) agree that only a few species should be recognized. Eltinge (personal communica- 

 tion, Sept., 1955), after a study of a collection of 88 cultures, reports that the group may 

 readily be separated into cultures that will grow at 4° but not at 37° C. and cultures that 

 will not grow at 4° but do grow at 37° to 42° C. This seems to be one of the most constant 

 of the differences in characters, and it is used in the classification drawn up by Cruess-Cal- 

 laghan and Gorman. 



There is a partial correlation between the growth-temperature relationships and the 

 ability to reduce nitrate (Eltinge, Antonie van Leeuwenhoek, £2, 1956, 139). Some cultures 

 (Chromobacterium violaceum) that may give a negative test for nitrite production actually 

 reduce the nitrate so rapidly with the production of free gas that they have sometimes 

 been reported in the literature as failing to reduce nitrate. Other cultures merely reduce 

 the nitrate to nitrite (Chromobacterium janthinum) , while still other cultures do not attack 

 nitrate at all. 



Corpe (Jour. Bact., 62, 1951, 515) found that he could readily isolate these organisms by 

 adding sterile rice grains to moistened soil. The latter observation confirms an earlier ob- 

 servation by Beijerinck (Folia Microbiologica, 4, 1916, 207) who added wheat bran or fibrin 

 to tap-water infusions in order to develop these violet bacteria. Starchy substances appear 

 to stimulate growth, as all grow abundantly on potato with a yellow growth that usually 

 turns to a dark violet or purple. 



A number of organisms have been classed as species of Chromobacterium because they 

 develop a bluish chromogenesis without regard to the fact that their pigments are not chem- 

 ically the same as violacein. The majority of these cultures are polar flagellate and have 

 been shown to belong to the genus Pseudomonas. Frequently these blue pigments are water- 

 soluble and have a tendencj^ to become rose-colored. 



The violet organisms differ in important respects from the organisms placed in Serratia. 

 The latter produce prodigiosin and belong with the coliform group. The violet organisms 

 show the same type of gummy colony growth that is characteristic of many of the species 

 found in Rhizobiaceae , their carbohydrate metabolism is like that of the species in this fam- 

 ily, and they possess the same unusual type of monotrichous to peritrichous flagellation. 

 The position of the violet bacteria in the family Rhizobiaceae appears to be a natural one. 



In recent j^ears these violet bacteria have been found in fatal septicemias in man and 

 animals (see Sippel, Medina and Atwood, (good bibliography). Jour. Amer. Vet. Med. 

 Assoc, 124, 1954, 467; Audebaud, Ganzin, Ceccaldi and Merveille, Ann. Inst. Past., 87, 1954, 

 413; and Black and Shahan, Jour. Amer. Med. Assoc, 110, 1938, 1270). These pathogenic 

 organisms have frequently been identified as Chromobacterium violaceum Bergonzini be- 

 cause they produce a violet pigmentation. However, by definition, this species does not 

 grow at 37° C. In the early literature C. janthinum Zopf was sometimes regarded as a sepa- 

 rate species, while in other cases C. violaceum and C. janthinuvi were regarded as identical. 

 Inasmuch as both Schroeter and Bergonzini, the investigators who first described C. vio- 

 laceum, grew their organisms at room temperature, and inasmuch as descriptions list them 

 as growing at room temperature while C. janthinum is normally described as growing best at 

 room temperature, Cruess-Callaghan and Gorman emended the descriptions of these two 

 species in such a way as to make C. violaceum the organism which will not grow at 37° C. 

 while they describe C. janthinum as growing at 37° C. In view of these emended descrip- 



