Abstract:Mesorhizobium loti MAFF303099 was used to construct a random mutant library with transposon Tn5-sacB mutagenesis technique.A total of about 10000 independent mutants were obtained.A method for rapidly identifying mutants from the library was established.The mutant of the symbiotic nodule gene nodB was identified through screening the mutant library.The results showed that the transposon Tn5-sacB was inserted into the genome DNA of all the mutants in the mutant library,with the tri-parental mating transformation efficiency of 3.75×10-5.The MAFF303099 mutant of nodB did not form nodules on Lotus japonicus roots comparing with the wildtype.