Genetic transfer of nitrogenase-hydrogenase activity in Rhodopseudomonas capsulata

THE transfer of nitrogen fixation ( nif ) genes to bacterial mutants defective in this capacity ( nif − ) by transduction 1 and conjugation 2 was first observed in 1971 with Klebsiella pneumoniae . The investigations cited and the subsequent demonstration 3 that nif genes can be transferred from K. pneumoniae to Escherichia coli have been widely regarded as harbingers of the molecular biology of the nitrogen fixation process. We now report a new system of interest in this connection, namely, the transfer of nif genes in the non-sulphur purple photosynthetic bacterium Rhodopseudomonas capsulata . Genetic transfer in this organism is mediated by a filterable vector of small size and unknown nature, the “gene transfer agent” (GTA), discovered by Marrs 4 .