14 Perspecfives in Microbiology 



prophage. If lysogeny were just the power to produce 

 phage, things would be relatively simple. Instead, they are 

 relatively complicated — though more fascinating — because 

 the prophage not only confers on the microbe the power 

 to manufacture phage but also may modify some of the 

 bacterial properties. The prophage modifies the response 

 of the microbe to infection by homologous and sometimes 

 heterologous phages. And sometimes the prophage may 

 endow the bacterium with properties that are, so far as 

 we know, without any relation to phage development 

 proper. 



Before discussing metapoietic integrations, it may be 

 well to summarize the essentials of lysogeny. The life cycle 

 of a temperate bacteriophage comprises three main phases: 

 first, the infectious phase, during which the phage is in 

 the form of the mature phage particle; second, the patho- 

 genic, vegetative phase, during which the specific struc- 

 tures of the phage are produced and finally organized; 

 third, the lysogenic phase, during which the power to pro- 

 duce phage is perpetuated by the lysogenic system. During 

 these three phases the genetic material of the bacterio- 

 phage, namely, the germ of the phage particle, the gono- 

 phage of the vegetative phase, and the prophage of the 

 lysogenic phase, must necessarily be the same in so far as 

 main architecture or organization is concerned. But the 

 germ is inert; the gonophage is multiplying rapidly, and 

 phage proteins are produced as a result of its activity; the 

 prophage is apparently just replicating harmoniously and 

 synchronously with the bacterium, as if it were a normal 

 bacterial gene. 



A number of experimental data have led to the conclu- 

 sion that prophage is the genetic material of the phage as 

 modified by its attachment to a specific locus of a bacterial 

 chromosome. In turn, the prophage modifies the proper- 

 ties of the bacterium as if it exerted an effect on bacterial 

 genes. Thus the properties of a lysogenic bacterium appear 



