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.
Highlights
Fifty three bacterial isolates investigated in this study were isolated from shrubs legumes nodules R. monosperma subsp. bovei var. oranensis (Maire) collected from three different coastal dunes of Oran city (North western area of Algeria) (Table 3)
Throughout many microbiological researches undertaken by several authors, it has been shown that Retama species have positive effects on their environment and vegetation in Iberian Peninsula and the Mediterranean coast due to their capacity to establish N2 fixing symbiosis with rhizobia
The rhizobia naturally associated with R. monosperma collected from three sites of the Oranian coastal have shown a wide morphological and physio-biochemical diversity
Summary
These plant species are of ecological interest in dune stabilization, soil fixation, and revegetation of semiarid and arid ecosystems (Herrera et al, 1993; Caravaca et al, 2002; Rodríguez-Echeverría and PerezFernandez, 2005). Retama could be useful as a tool for restoration, providing long term plantations without artificial aid and allowing primary succession (Singh et al, 2002)
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