title: Effect of thorium on the growth and capsule morphology of Bradyrhizobium.
abstract: The thorium effect on Bradyrhizobium growth was assayed in liquid media. Th4+ inhibited the growth of Bradyrhizobium (Chamaecytisus) BGA-1, but this effect decreased in the presence of suspensions of live or dead bacterial cells. Th4+ induced the formation of a gel-like precipitate when added to a dense suspension of B. (Chamaecytisus) BGA-1 cells. Viable Bradyrhizobium cells remained in suspension after precipitate formation. Thorium was recovered in the precipitate, in which polysaccharide, lipopolysaccharide and proteins were also found. After Th4+ addition, the morphology of B. (Chamaecytisus) BGA-1 or Bradyrhizobium japonicum USDA 110 sedimented cells studied by scanning electron microscopy changed from an entangled network of capsulated bacteria to uncapsulated individual cells and an amorphous precipitate. Energy-dispersive X-ray spectroscopy showed that thorium was mainly in the amorphous fraction. Precipitate was also formed between B. (Chamaecytisus) BGA-1 and Al3+, which was also toxic to this bacterium. Precipitate induced by Th4+ or Al3+ was found in all Bradyrhizobium and Sinorhizobium strains tested, but not in Rhizobium, Salmonella typhimurium, Aerobacter aerogenes or Escherichia coli. These results suggest a specific defence mechanism based on metal precipitation by extracellular polymers.
mesh_terms: D000535:Aluminum / Q000494:pharmacology; D016667:Bacterial Capsules / Q000187:drug effects* / Q000378:metabolism; D020369:Bradyrhizobium / Q000187:drug effects / Q000254:growth & development* / Q000648:ultrastructure*; D011232:Chemical Precipitation; D006863:Hydrogen-Ion Concentration; D011135:Polysaccharides, Bacterial / Q000378:metabolism / Q000494:pharmacology; D013696:Temperature; D013910:Thorium / Q000494:pharmacology*
chemical_list: D011135:Polysaccharides, Bacterial; D013910:Thorium; D000535:Aluminum