Identification of the endosymbionts from Sulla spinosissima growing in a lead mine tailings in Eastern Morocco as Mesorhizobium camelthorni sv. aridi

Aims: To identify the bacteria nodulating Sulla spinosissima growing profuselyin a lead and zinc mine tailings in Eastern Morocco. Methods and Results: In all, 32 rhizobial cultures, isolated from root nodules of S. spinosissima growing in soils of the mining site, were tolerant to different heavy metals. The ERIC-polymerase chain reaction (PCR) finger printing analysis clustered the isolates into seven different groups, and the analysis of the 16SrRNA sequences of four selected representative strains, showed they were related to different species of the genus Mesorhizobium.TheatpD, glnII and rec Ahousekeeping genes analysis confirmed the affiliation of the four representativestrains to Mesorhizobium camelthorni CCNWXJ40-4T, with similarity percentages varying from 96.30 to 98.30%. The sequences of the nifH gene had 97.33–97.78% similarities with that of M. camelthorni CCNWXJ40-4T; however, the nodC phylogeny of the four strains diverged from the type and other reference strains of M. camelthorni and formed a separated cluster.The four strains nodulate also Astragalus gombiformis and A. armatus but did not nodulate A. boeticus, Vachellia gummifera, Prosopis chilensis, Cicer arietinum, Lens culinaris, Medicago truncatula, Lupinus luteus or Phaseolus vulgaris. Conclusions: Based on similarities of the nodC symbiotic gene and differences in the host range, the strains isolated from S. spinosissima growing in soils ofthe Sidi Boubker mining site may form a different symbiovar within Mesorhizobium for which the name aridi is proposed. Significance and Impact of the Study: In this work, we show that strains ofM. camelthorni species nodulating S. spinosissima in the arid area of Eastern Morocco constitute a distinct phylogenetic clade of nodulation genes; wenamed symbiovar aridi, which encompasses also mesorhizobia from other Mediterranean desert legumes.