Three chickpea rhizobial strains (CCBAU 83963 T , CCBAU 83939 and CCBAU 83908), which were identified previously as representing a distinctive genospecies, were further studied here and compared taxonomically with related species in the genus Mesorhizobium. Results from SDS-PAGE of whole-cell soluble proteins revealed differences from closely related recognized species of the genus Mesorhizobium. ; only Cicer arietinum, its host plant, could be invaded to form effective nitrogen-fixing nodules. The narrow spectrum of utilization of sole carbon sources, lower resistance to antibiotics, and NaCl, pH and temperature growth ranges differentiated these novel rhizobia from recognized species of the genus Mesorhizobium. Based on the data presented, the three novel rhizobial strains are considered to represent a novel species of the genus Mesorhizobium, for which the name Mesorhizobium muleiense sp. nov. is proposed. The type strain is CCBAU 83963 T (5HAMBI 3264 T 5CGMCC
T ).Previously, the predominant symbiotic nitrogen-fixing bacteria associated with chickpea (Cicer arietinum L.) in Europe and in India have been classified as members of the genus Mesorhizobium, including Mesorhizobium ciceri, Mesorhizobium mediterraneum, Mesorhizobium amorphae, Mesorhizobium loti and Mesorhizobium tianshanense (Laranjo et al., 2004(Laranjo et al., , 2008L'taief et al., 2007; Maâtallah et al., 2002;Nandwani & Dudeja, 2009;Nour et al., 1994Nour et al., , 1995 Rivas et al., 2007). Similarly, 95 chickpea nodule isolates collected from alkaline soil in Xinjiang, China, in our previous study were identified as representing a novel Mesorhizobium genomic species closely related to Mesorhizobium temperatum, M. mediterraneum and Mesorhizobium robiniae based on genomic analyses, including BOX-PCR, 16S rRNA PCR RFLP, intergenic spacer PCR RFLP, multilocus sequence analysis (MLSA) and DNA-DNA hybridization (DDH) studies (Zhang et al., 2012).To determine the taxonomic status of these chickpea rhizobia, phenotypic characteristics, cross-nodulation tests, fatty acid profiles and other genetic information were further investigated and compared with related species in the current study. Based on the evidence from previous and the current study, these chickpea rhizobia are considered to represent a novel species of the genus Mesorhizobium.In the present study, the bacterial strains were cultured at 28 u C on modified-yeast mannitol agar mediumAbbreviations: DDH, DNA-DNA hybridization; MLSA, multiple locus sequence analysis.The GenBank/EMBL/DDBJ accession numbers for the 16S rRNA, recA, glnII, atpD, nodC and nifH gene sequences of strain CCBAU 83963
