SI X IN BACTERIA— EVIDENCI-: FROAI MORPHOLOGY 37 



Agrobiicterhmi tiivicjaciens, the causative agent of crown gall in 

 plants, produces star-shaped aggregates of cells in which the cells ap- 

 pear to radiate from a common center. Lohnis (1921) interpreted 

 such aggregates as conjunction. The term conjunction was used rather 

 than conjugation because frequently more than two cells unite and 

 there is no detectable sexual differentiation among them. The be- 

 havior of the nuclear material in such "stars" was studied with the 

 aid of the Feulgen reaction by Stapp (1942) and later by Braun and 

 EIrod (1946). These investigators suggest that nuclear material from 

 the component organisms fuses in the center of the aggregate; al- 

 though, as Braun and Elrod have pointed out, in many of the aggre- 

 gates the Feulgen-positive material remained confined to the cell but 

 concentrated in that part of the bacterium closest to the center of the 

 star. They, therefore, were reluctant to interpret the phenomenon as 

 conjugation because of the relatively few instances in which they 

 observed what appeared to be an actual fusion of nuclear material. 



Using the same method of approach, the study of fixed and 

 stained cells, DeLamater (1951) described the process of conjugation 

 in Bacillus megaterimn. Vegetative cells, considered to be haploid, 

 form conjugation tubes which are attached to only one cell or form 

 a connection between the ends of two cells. At times a pair of tubes 

 was observed connecting the ends of two cells or a loop-like struc- 

 ture formed on the side of a chain of rods connecting two cells of the 

 chain. The extension of a conjugation tube from the end of one cell 

 into the side of another in a different chain was taken as evidence that 

 two cells of distinct origin could fuse. The simultaneous fusion of 

 three rods was also observed on one occasion. The nuclei are de- 

 scribed as migrating in both directions through these tubes so that 

 both of the cells are usually "diploidized." Subsequently, it is claimed, 

 the nuclei fuse and the cells enlarge and multiply vegetatively as dip- 

 loids. 



DeLamater has observed conjugation tubes on blood agar base 

 plus 4 per cent human whole blood, on casein hydrolyzate medium, 

 and in all the various sugars in which secondary colonies form. It 

 was presumed that a relationship may exist between conjugation and 

 secondary colony formation. The results from one series of experi- 

 ments, however, show that, although secondary colonies can form on 

 media containing blood or serum from different animals, conjugation 

 tubes are formed only on media containing whole blood, plasma, or 



