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1 Key Laboratory of Agro-Microbial Resource and Application, Ministry of Agriculture/College of Biological Sciences, China Agricultural University, Beijing 100094, PR China
2 Departamento de Microbiología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, 11340 México D.F., México
3 The Institute of Agricultural Resources and Regional Planning of Chinese Academy of Agricultural Sciences. Beijing 100081, PR China
Correspondence
Wen Xin Chen
wenxin{at}cau.edu.cn
Thirty-one rhizobial strains isolated from nodules of legumes native of Xinjiang, China, were characterized. These strains were classified as belonging to the genus Rhizobium based on amplified 16S rDNA restriction analysis (ARDRA). The strains were distinguished from recognized Rhizobium species using analysis of 16S–23S rDNA intergenic spacers (IGS-RFLP), SDS-PAGE analysis of whole proteins and BOX-PCR; the test strains always formed a distinct cluster with patterns that were quite different from those of the reference rhizobial strains used. According to the phylogenetic analysis based on the 16S rRNA gene, the test strains belonged to the genus Rhizobium, with Rhizobium tropici, Rhizobium rhizogenes and Rhizobium lusitanum as the closest related species, with 99.6, 99.2 and 99.4 % sequence similarities, respectively, between the type strains of the three Rhizobium species and strain CCBAU 83401T. Phylogenetic analyses of the representative strains using IGS and atpD, recA and glnII genes all confirmed the phylogenetic arrangements obtained using the 16S rRNA gene. The DNA–DNA relatedness values between strain CCBAU 83401T and strains CCBAU 83364, CCBAU 83345 and CCBAU 83523 ranged from 80.8 to 100 %, showing that they belong to the same species. The DNA–DNA relatedness between strain CCBAU 83401T and R. tropici IIB CIAT 899T, R. tropici IIA CFN 299, R. rhizogenes LMG 150T and R. lusitanum P1-7T were 26.9, 27.7, 38.2 and 22.6 %, respectively, clearly indicating that strain CCBAU 83401T represents a novel species. Phenotypic characterization of four representative strains, CCBAU 83401T, CCBAU 83364, CCBAU 83345 and CCBAU 83523, showed several distinctive features that differentiated them from closely related species. The 31 strains had identical nodD and nifH genes, which were very similar to those of the bean-nodulating R. lusitanum, Devosia neptuniae and R. tropici IIB. Based upon these results, the strains from this study are considered to represent a novel species, for which the name Rhizobium multihospitium sp. nov. is proposed. The DNA G+C content ranged from 65.3 to 66.0 mol% (Tm). The type strain is CCBAU 83401T (=LMG 23946T=HAMBI 2975T), which nodulates Robinia pseudoacacia, but not Leucaena leucocephala, Phaseolus vulgaris, Pisum sativum or Medicago sativa.
The GenBank/EMBL/DDBJ accession numbers for the 16S rRNA gene sequences of strains CCBAU 83401T, CCBAU 83333, CCBAU 83375, CCBAU 83277, CCBAU 83345, CCBAU 83319, CCBAU 83325, CCBAU 83364, CCBAU 83435, CCBAU 83503 and CCBAU 83523 are EF035074, EF035062, EF035065, EF035067, EF035059, EF490013, EF035069, EF490014, EF035070, EF035076 and EF035077, respectively. Those for partial IGS sequences are EF490015, EF050766, EF490016, EF050762, EF050763, EF050764, EF050761, EF490017, EF490018, EF050760 and EF050765, respectively; those for partial glnII gene sequences are EF490040–EF490050, respectively; for partial recA gene sequences are EF490029–EF490039, respectively; for partial atpD gene sequences are EF490019–EF490024, EU130792 and EF490025–EF490028, respectively; for partial nodD gene sequences are EF490051–EF490056, EF549532 and EF490057–EF490060, respectively; and for partial nifH gene sequences are EF490070, EF490061–EF490065, EF549533 and EF490066–EF490069, respectively.
Dendrograms based on IGS–RFLP fingerprints, SDS–PAGE of proteins and BOX-PCR and phylogenetic trees based on sequences of the 16S rRNA gene, IGS and atpD, recA, glnII, nodD and nifH genes of the test rhizobial strains and reference strains of recognized Rhizobium species and a table showing the fatty acid profile of strain CCBAU 83401T and those of closely related taxa are available as supplementary material with the online version of this paper.
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