Thenodgene inducer genistein alters the composition and molecular mass distribution of extracellular polysaccharides produced byRhizobium frediiUSDA193

The nodulation genes of Rhizobium fredii are located on large symbiosis plasmids and induced by flavonoid signals from the host plant. When cultured in the presence of the isoflavone nodulation gene inducer, genistein, R. fredii USDA193 produced extracellular polysaccharide (EPS) with a lower average molecular mass and a reduced uronic acid content in comparison to controls. Genistein treatment also attenuated the yield of these compounds. These genistein-mediated changes are dependent on the presence of the symbiosis plasmid and were not apparent with the plasmid-cured, non-nodulating derivative, IA728. In addition, EPS yields from IA728 were higher than those from USDA193, indicating that the sym plasmid is involved in the regulation of EPS production, independent of the presence of genistein signals.