Isolation and properties of antimicrobial substance produced by Sinhorhizobium melilloti from root nodules of Medicago sativa

Abstract

The symbiotic association of alfalfa (Medigaco sativa) with Sinorhizobium melilloti contributes to the production of inoculum to improve plant growth and increase yield. The competitiveness of the introduced strains is a very important factor in the performance of an inoculum which is based on the use of rhizobial strains. This competitiveness is due to the production of anti-microbial substances, among them, bacteriocines. In this study, the totals of 30 rhizobial strains were isolated from M. sativa nodules sampled from sa-line soils of Algeria. Twenty strains were nodulated the host plant M. sativa. The antimicrobial activity producing strains SW16 and SW15 were identified as Sinorhizobium melliloti based on 16S rRNA sequance analysis. Partial puri-fication of this inhibitorys substances by ammonium sulfate were precipitat-ed with 75% saturation. These antimicrobial activitys showed the maximum activity against the strain SW10 estimated at 1800 with the strain SW16 and 2500 AU/ml for the strain SW15. The physicochemical properties of these antimicrobial activitys reveals thier thermoresistant nature and sensitive to protease, but theire were resistant to a wide range of pH and also at differ-ent concentrations of Nacl. This inhibitory agent display primary metabolite kinetics as its maximal production was detected in the growth phase. Antimi-crobial substances produced by sinorhizobium mielilloti SW15 and SW16 exhibited inhibitory activity against the phytopathogen (Aspergillus sp., Fusarium sp., Cladosporium sp. and Alternaria altterna).