Mesorhizobium muleiense sp. nov., nodulating with Cicer arietinum L.

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. Levels of DNA-DNA relatedness were 15.28-50.97% between strain CCBAU 83963(T) and the type strains of recognized Mesorhizobium species (except for Mesorhizobium thiogangeticum). Strain CCBAU 83963(T) contained fatty acids characteristic of members of the genus Mesorhizobium, but it possessed high concentrations of C(19:0) cyclo ω8c and iso-C(17:0). Strain CCBAU 83963(T) had phosphatidylcholine, phosphatidylethanolamine and phosphatidylglycerol as major polar lipids, and an ornithine-containing lipid, phosphatidyl-N-dimethylethanolamine and cardiolipin as minor components. Nodulation tests demonstrated the distinct symbiotic character of strain CCBAU 83963(T); 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) (=HAMBI 3264(T)=CGMCC 1.11022(T)).