Phenotypic and genotypic characterizations of rhizobia isolated from root nodules of multiple legume species native of Fez, Morocco

Root-nodulating bacteria were isolated and characterized from grain and forage legumes growing in Fez regions. A total of 110 Rhizobium strains were characterized on the basis of morphological, cultural, and phenotypical properties. Phenotypic characteristics studied included growth rates in various media, colony morphology, tolerances to extremes of temperature, salt and pH and resistance to different concentrations of heavy metals and antibiotics. The isolates were very diverse phenotypically. Eighty seven of isolates were fast growing rhizobia. Thirty four strains tolerated high concentration of salt (2% NaCl). The majority of our isolates tolerated temperatures ranging between 20 and 37 degrees C, but not above 55 C. Also, the isolated strains tolerated extreme pH in their medium from 4.8 to 8.8. The antibiotic resistance of these strains showed a high level of resistance against streptomycin, kanamycin, ampicillin, tetracycline, and chloramphenicol. The highest resistance to heavy metals was recorded for arsenate, copper, zinc, nickel, and mercury. Also, a moderate resistance was found for chromium. Polymerase chain reaction (PCR) method and 16S rRNA gene sequencing were used for the genotypic analysis of 17 Rhizobium strains selected on the basis of phenotypic study. The results showed a high diversity among the strains.