Avissar, Y.J., Department of Biology, Ben Gurion University of the Negev, Be’er Sheva, 84120, Israel
Gollop, R., Department of Biology, Ben Gurion University of the Negev, Be’er Sheva, 84120, Israel

The symbiotic state of Rhizobium can be simulated by microaerobic culture conditions. These conditions inhibit or restrict growth and permit differentiation of the bacterium to a state similar to the bacteroid found in legume nodules in the following characteristics: morphology (cells are swollen and pleiomorphic); capability of nitrogen fixation as indicated by acetylene reduction; increased production of intermediates required for heme production and increased heme content; absence of cytochrome aaz; presence of an active nitrate reductase in the absence of nitrate in the medium. Microaerobically grown rhizobia can therefore be considered as being pseudobacteroids, an important tool for studying the legume-Rhizobium symbiosis in the laboratory. © 1982 Taylor & Francis Group, LLC.