Inhibition of growth of Bradyrhizobium japonicum bacteroid by spermidine and spermine in yeast extract

Abstract

Bacteroids are defined as the symbiotic forms of Rhizobium or Bradyrhizobium cells in the root nodules of their legume host. The differentiation to bacteroids involves various physiological changes and may be associated with some genetical changes. Single-colony isolates from a nodule formed by a Bradyrhizobium strain often differed in their effectiveness and intrinsic antibiotic resistance (Weaver and Wright 1987; Ozawa unpublished data). Detailed analysis of the changes in the gene structure requires the isolation of individual bacteroids from a nodule. However it has been reported that the viability of bacteroids in culture is very low and only a small fraction of a bacteroid population could produce colonies on yeast extract-mannitol (YEM) agar (Sutton et al. 1977). Bergersen (1974) concluded that the reversion of bacteroids to the vegetative, growing form is very rare.