Isolation and characterization of endophytic non-rhizobial bacteria from root nodules of alfalfa (Medicago sativa L.).

✳Abstr Act Soil bacteria associated with plant roots that can exert beneficial effects on their hosts are designated as plant growth promoting rhizobacteria (PGPR). Some of these PGPR can enter the root interior and establish endophytic populations. The present study was performed to isolate non-rhizobial endophytes from the surface sterilized root nodules of alfalfa (Medicago sativa L.) and assess their effects on alfalfa growth. Out of 15 endophytic non-rhizobial strains isolated, 5 gram-positive strains were selected for further identification and characterisation. The strains LR1k, 4148pk and SNji formed one single cluster in rep-PCR analyses and partial sequences of 16S rRNA genes showed 100% similarity to Bacillus megaterium. Strains 251s and 236 displayed two separate rep-PCR patterns and according to 16S rRNA genes sequences they were closely related to Brevibacillus chosinensis and Microbacterium trichothecenolyticum, respectively. None of the non-rhizobial isolates was able to nodulate alfalfa when re-inoculated in gnotobiotic culture. Co-inoculation of all non-rhizobial strains with S. meliloti positively influenced nodule number of alfalfa, but was without significant effect on growth parameters with respect to inoculation with S. meliloti alone. However, single inoculation with non-rhizobial strains caused significant increase in shoot and root parameters compared to uninoculated plants, indicating that non-rhizobial strains possess some plant growth promoting potential. Further studies on the interactions among these endophytic bacteria and other legumes or non-leguminous plants are needed.