Characterization of rhizobia isolated from Carob tree (Ceratonia siliqua)

Bacteria were isolated from root nodules of Carob tree (Ceratonia siliqua). We studied their cultural, physiological and biochemical characteristics. Strains showed some variability concerning tolerance to NaCl and KCl, and none grew at pHs below 7. The mean temperature for growth was 30°C and some strains could grow at 45°C. These isolates could use a great variety of carbohydrates as a sole carbon source (hexoses, pentoses, disaccharides, trisaccharides, polysaccharides and organic acids). According to their cultural and physiological features and their in vitro infectivity on their original host, we suggest that these isolates may belong to the genus Rhizobium. Moreover, with regard to their average generation time, carbohydrate utilization, antibiotic resistance and other biochemical properties, they may be related to fast-growing rhizobia until further characterization.