[Effect of host change on phages 223 -17 and 7591-14 Pseudomonas savastanoi pv. tabaci]

We studied the characteristics of phages 223-17 7591-14 grown on the strains of Pseudomonas syringae pv. tabaci, on the intermediate host of P. savastanoi pv. phaseolicola and after their returning to original. It was found, that phages grown on pv. phaseolicola acquired ability to cause lysis of previously resistant strains P. viridiflava (phage 223-17) and P. fluorecens (phage 7591-14). It was common that, when making the restriction analysis of DNA of phages grown on pv tabaci, the formation of additional minor fragments was observed along with the major fragments. Phage DNA did not change its length then. Two minor EcoRV fragments of DNA identical by length, were found in both phages in the first studies. If they changed the host, they disappeared. Once again returning to the first host the authors found previously absent, additional minor HindIII fragments of DNA. The phage 7591-14 had two fragments, while the phage 223-17 had one fragment. Formation of minor EcoRV DNA fragments is obviously connected with the emergence of an additional restriction site, since the sum of their lengths is equal to the size of one of the major fragments. Minor HindIII fragments whose size was equal to the sum of the lengths of two and three major fragments could be formed as a result of the loss of several restriction sites. Since the effect of the host enzyme systems on phage DNA was accompanied by the synchronous acquisition or loss of minor DNA fragments, it is obvious that this process is not of a random nature. Weak luminescence of the minor fragments of considerable length indicates that their part in the total pool of DNA is small. The observed changes of phages seem to be associated with the process of their adaptation to different hosts.