Genetic transfer of nitrogen fixation from Rhizobiumtrifolii to Klebsiellaaerogenes

Summary The transfer of genes controlling N 2 -fixation from Rhizobium trifolii to Klebsiella aerogenes 418, a strain incapable of fixing nitrogen, is reported. This intergeneric transfer was mediated by an F-like R-factor which had previously been transferred into the R. trifolii . The Nif operon was transferred at a frequency of 10 −7 or higher. The K. aerogenes hybrids reduced acetylene at rates similar to a naturally occurring N 2 -fixing strain, K. pneumonia M5a1. Acetylene reduction was supressed in the presence of oxygen or combined nitrogen. While the results presented are consistent with the general conclusion that Nif genes were transferred from R. trifolii to K . aerogenes the possibility that the transfer of genetic material from R. trifolii permitted the expression of latent Nif genes in K. aerogenes must remain an alternate consideration. This report is the first evidence that Rhizobium contains genetic information specifying functions involved in nitrogen fixation.