EXOPOLYSACCHARIDE-DEFICIENT MUTANTS OF ASTRAGALI RHIZOBIA ARE SYMBIOTICALLY EFFECTIVE ON ASTRAGALUS-SINICUS, AN INDETERMINATE NODULATING HOST

Five exopolysaccharide-deficient mutants were isolated after rhizobial strain 107 was subjected to transposon Tn5 mutagenesis. The amount of EPS produced by the mutants was dramatically decreased to between 3% and 6% of wild-type level. All mutants carried a singel copy of Tn5. T wo mutants (NA3 and NA10) were complemented by the R. meliloti exoA ge ne and the functionally equivalent exoD gene of Rhizobium sp, strain N GR234. Two other mutants (NA7 and NA8) were complemented by the R. mel iloti exoB gene and the functionally equivalent NGR234 exoC gene. The remaining mutant (NA11) was not complemented by any exo genes of R. me liloti or Rhizobium NGR234. All mutants induced normal nitrogen-fixing nodules on Astragalus sinicus, an indeterminate nodulating host.