Abstract
Thirty root-nodulating bacteria isolates were obtained from the roots of Acacia ampliceps (Maslin), A. ehrenbergiana (Hayne.), A. saligna (Labill.), A. seyal (Del.), A. tortilis (Forssk.), A. tortilis subsp. raddiana (Savi.), Leucaena leucocephala (Lam.) and Vicia faba (L.) trees growing in the Riyadh region. The isolates' phenotypic and biochemical properties were characterized by assessing colony appearance, growth rate, resistance to antibiotics and heavy metals, and tolerance to salinity, elevated temperature and pH. All isolates had same colony morphology and grew on yeast extract mannitol and tryptone yeast agar, but not MGS media. The results also revealed considerable diversity among the isolates, which exhibited different patterns of resistance to abiotic stresses. Most isolates tolerated temperatures up to 37 degrees C and could grow from pH 5.5-8.5 and at a high NaCl concentration (2% w/v). The majority of isolates could utilize a variety of carbohydrates. Most of the isolates displayed resistance to antibiotics in the 75 mu g ml(-1) range, with similar to 100 mu g ml the maximum concentration at which growth was observed. All isolates were sensitive to aluminum and resistant to other heavy metals tested, and they were able to reduce nitrate and hydrolyze urea.