Succinate-Induced Morphology of Rhizobium trifolii 0403 Resembles That of Bacteroids in Clover Nodules.

Morphological changes which accompany nutrient enrichment of Rhizobium trifolii 0403 were studied. Assays of cell number and size coupled with scanning electron microscopy and immunofluorescence microscopy showed that succinate induces cells to stop dividing in vitro and to swell either in the cell center or at one cell pole. The extent and frequency of in vitro cell swelling were in direct relation to the concentration of succinate added to the enrichment medium. The in vitro swelling of cells in 16.6 mM succinate plus Casamino Acids, glucose, and yeast extract closely resembled that of bacteroids of R. trifolii 0403 in nitrogen-fixing nodules of white clover. We hypothesize that succinate may be involved in the transformation of vegetative bacteria into the bacteroid morphology found in nitrogen-fixing nodules.