28. Agrobacterium 



The genus Agrobacterium in Bergey's Manual is grouped 

 together with Rhizobium and Chromobacterium in the family 

 Rhizobiaceae. The more typical species of Agrobacterium such as 

 Agrobacterium tumefaciens, Agrobacterium rhizo genes, and Agro- 

 bacterium radiobacter are very similar, both physiologically and 

 morphologically, to the peritrichously flagellated species of Rhizo- 

 bium. Chromobacterium, however, is so radically different that the 

 author sees little justification for grouping it in the same family as 

 Agrobacterium and Rhizobium. 



Cultures 



Sixteen cultures of Agrobacterium were studied over a period 

 of several years. Eight strains of various species came from Morti- 

 mer P. Starr of the University of California, two strains from Joel 

 Hildebrant of the University of Wisconsin, and the others from 

 various sources. All the cultures were carefully checked physio- 

 logically. Typical species of Agrobacterium oxidize, but do not 

 ferment, carbohydrates. The oxidation of sucrose by these bacteria 

 seems particularly noteworthy. With the exception of Agrobac- 

 terium. gypsophilae, Starr TG-101, all cultures were physiologically 

 typical of the genus. This culture of A. gypsophilae was a poorly 

 flagellated, peritrichous rod which fermented carbohydrates. It 

 could be a species of Erwinia but not Agrobacterium. 



Flagellar Characteristics 



The cultures studied were rather poorly flagellated with the 

 majority of the individuals without flagella. One or two flagella 

 per flagellated individual was most common with a few individuals 

 having three to four flagella but rarely more. The arrangement of 

 the flagella was peritrichous. In common with other poorly flagel- 

 lated peritrichous rods the flagella show a strong tendency to 

 originate at or near the somatic poles. The general appearance of 

 the flagella of A, tumefaciens, A. radiobacter, and A. rhizogenes 

 was very similar, and no variants were observed. The average 

 wavelength of A. tumefaciens was 1.45 microns, of A. radiobacter 

 1.49 microns, and of A. rhizogenes 1.47 microns. These wave- 



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