Virulent bacteriophage infection of Rhizobium leguminosarum

Abstract

Bacteriophage 317, which virulently infects Rhizobium leguminosarum, has an eclipse period of 60–70 min and a latent period of 100 min at 30°. Electron micrographs of the phage indicated head, tail, and tail-fiber structural components.Base analysis of phage 317 deoxyribonucleic acid (DNA) indicated the presence of equimolar amounts of adenine and thymine and of guanine and cytosine, which suggests that the DNA is double stranded. The DNA has a molecular weight of 41 × 106 daltons as determined from electron micrographs.The results of 14C-uracil incorporation studies showed that net ribonucleic acid (RNA) synthesis was markedly inhibited after infection. There was a slight stimulation in DNA synthesis after infection as indicated by 14C-thymidine incorporation.The results of in vitro assays of enzymes involved in the biosynthesis of DNA showed that deoxyuridine 5′-triphosphate nucleotidohydrolase (dUTPase) and deoxythymidine 5′-monophosphate kinase (dTMP kinase) increased 50- and 30-fold respectively, after infection. The reason for the increased dUTPase activity is not readily apparent. Phage 317 DNA contains only the standard bases, unlike the DNA of other phages that induce an increase in this enzyme after infection. A high level of deoxythymidine 5′-monophosphatase (dTMPase) was observed in both uninfected and infected crude cell extracts. Further work is necessary to see if similar changes occur in Rhizobium during the establishment of symbiosis with legumes.