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A Gram-strain-negative, rod-shaped, motile bacterium, designated MIM27(T), was isolated from the sand of the Mu Us Desert, PR China. The strain could grow at 4-45 degrees C (optimum, 37 degrees C), at pH 6.6-9.0 (optimum, 8.0) and in the presence of 0-3% (w/v) NaCl (optimum, 0% in RNA liquid medium). The results of phylogenetic analysis of 16S rRNA gene sequences indicated that the strain represented a member of the genus Rhizobium, with the highest similarity (96.5 %) to Rhizobium pakistanense BN-19(T). The results of analysis of the sequences of the nitrogen fixation gene nifH and three housekeeping genes, recA, atpD and glnII, also indicated that MIM27(T) was most closely related to the species of the genus Rhizobium with validly published names but the similarities were low (<= 90.7 %). MIM27(T) did not form nodules on Pisum sativum, Vicia faba, Astragalus sinicus and Phaseolus vulgaris. The major respiratory quinone of MIM27(T) was Q-10. The genomic DNA G+C content was 59.8 mol%. Major fatty acids of MIM27(T) were summed feature 8 (C-18 : 1 omega 7c and/or C-18 : 1 omega 6c), C-18 : 1 omega 7c 11-methyl, C-16 : 0, summed feature 3 (C-16 : 1 omega 7c and/or C-16 : 1 omega 6c) and summed feature 2 (C-12 : 0 aldehyde and/or unknown ECL 10.9525). On the basis of the physiological, chemotaxonomic and phenotypic data, MIM27(T) is suggested to represent a novel species of the genus Rhizobium, for which the name Rhizobium arenae sp. nov. is proposed. The type strain is MIM27(T) (=KCTC 52299(T)=MCCC 1K03215(T)).