Preliminary characterization of slow growing rhizobial strains isolated from Retama monosperma (L.) Boiss. root nodules from Northwest coast of Algeria

Abstract

In this paper, we did some preliminary characterization of six slow growing rhizobial strains, isolated from Retama monosperma (L.) Boiss. root nodules sampled from 3 sites along the coast of Oran (CapeFalcon, Bousfer and MersElHadjadj) in Northwestern Algeria. Results of this study showed that all strains had a very slow growth rate in yeast malt (YM) agar medium, forming colonies less than 1 mm in diameter after seven days incubation. Catalase, oxidase and urease were positive, 3-ketolactose was negative. All strains resisted alkaline pH up to 9 and salinity equal to 2% (w/v) NaCl. They grew from 14 to 30°C with optimum growth at 28°C which is related to their place of presence (marine sand dunes Mediterranean climate). The strains used are, on the one hand D-glucose and D-galactose as carbon source and on the other hand L-leucine, L-tyrosine as nitrogen source. The nodulation tests performed pointed out that the total dry weight of the plant could go up to 1.7 g per plant and the maximum number of nodules was equal to 5.6 nodules per plant for the strain RMB1 from Bousfer site. The intrinsic antibiotic resistance level in all strains was tested against nine antibiotics; they revealed a variability of resistance against spectinomycin (10 μg , erythromycin (15 μgml^-1, rifampicin (30 μgml^-1), streptomycin (500 μgml^-1), kanamycin (30 μgml^-1), naldixic acid (30 μgml^-1), penicillin (6 μgml^-1) and tetracycline (30 μgml^-1) except for gentamycin (500 μgml^-1). The results of electrophoresis on 0.7% agarose gel showed the presence of chromosomal DNA and absence of plasmids.

Key words: Retama monosperma (L.) Boiss., Bradyrhizobium, symbiosis, root nodules, nitrogen fixation, endemic legumes, Algeria.