SEX IN BAG ll'.RIA— GENETIC S lUDIES 25 



cally much simpler than the intact cell; in E. colt, no unit other than 

 the cell has been shown to be active in recombination. 



A search for recombination in Sahnonella typhimur'mm, a species 

 distantly related to E. coli, has led to the discovery of another mode 

 of transduction. In this system occasional bacteriophage particles ap- 

 pear to become fortuitously contaminated with genetic fragments 

 from the host cells on which they are grown, and to be able to trans- 

 duce these fragments to new cells which they may invade without 

 killing them. The fragments retain their activity, and somehow enter 

 the genetic organization of the new host. In this way, for example, 

 flagellar antigenic traits from S. ty phivmrium may be introduced into 

 cells of 5". typhi to give a hybrid serotype or species not previously 

 described (Zinder and Lederberg, 1952). The possibilities that sexual 

 recombination may occur in Sabnofiella or that a genetic transduc- 

 tion may be found in E. coli are not unlikely, in view of the taxo- 

 nomic relationship of these bacteria. It is from a superposition of these 

 phenomena in a single species that we may expect to learn the most 

 about each of them. At present, however, they appear to be quite 

 distinct. 



To sum up the present status of our knowledge of sexuality in 

 E. coli, it has been shown that in mixed cultures under suitable condi- 

 tions a small but significant number of cells of certain strains of this 

 organism undergo a process of recombination of genes governing a 

 wide variety of characters. This process apparently involves a cell-to- 

 cell contact, and presumptively copulation, or conjugation, with 

 zygote formation. Analysis of the recombination products indicates 

 that the genes are present in linear order on one or more chromo- 

 somes. In essence, then, certain strains of E. coli, especially K-12, are 

 capable of a sexual process, analogous in so far as it has yet been 

 analyzed to that of other organisms. 



It is to be hoped and expected that sexual phenomena will not 

 be limited to E. coli among the bacteria. It is likewise to be hoped 

 that the significance of suggestive cytological phenomena in bacteria 

 such as apparent conjugation tubes (DeLamater, 1951), star-body 

 formation (Braun and Elrod, 1946), filterable L-forms (KHeneberger- 

 Nobel, 1951) and large bodies (Dienes, 1946; Stempen and Hutchin- 

 son, 1951) can be further evaluated by genetic analysis involving the 

 recombination and tracing of suitable genetic markers. 



The future also holds not only promise of correlation of genetic 



