Effect of salt stress on endophytic bacteria isolated from root of Momordica charantia

Salinity is one of the most critical constraints which hamper agricultural production in many areas world wide. One of the most recently gaining practices of counteracting the adverse effect of salinity on plant growth is the inoculation of salt tolerance bacteria with PGP traits. The endophytes are non-pathogenic plant associated bacteria that can play an important role in plant vitality and may confer resistance to abiotic or biotic stresses. Endophytic bacteria were isolated from the roots of Momordica charantia , by following the various techniques identified and characterized . Bacterial clones were isolated by plating the surface sterilized root suspension on LB nutrient agar in anaerobic gas jar and identified on the basis of their morphological characteristics following the standard microbiological techniques and practices. Their biochemical characterization were made as described in Bergey’s manual systematic bacteriology (1984) finally the clones were identified using the molecular techniques of 16s ribosomal RNA gene sequencing and their phylogenetic relationship based on non-joining cluster analysis. Out of 18 endophytic bacterial strains, 8 strains were finally selected based on colony morphology. The strains characterized using morphological, physiological and biochemical criteria accompanied with 16S rRNA gene sequencing.  All the eight strains showed closest similarity with Bacillus, Agrobacterium, Lysinibacillus and Uncultured bacterial clone. The 16S rRNA gene sequencing revealed that the endophytic bacteria belonged to phylogenetic division Firmicutes and β- Proteobacteria. The dominant endophytic bacteria of bitter gourd were firmicutes. The above bacteria were characterized as endophytic bacteria on the basis of enzymatic activity. All the endophytic bacteria showed stress tolerance. They were able to tolerate 4% NaCl concentration and above this concentration their responses vary. Two strains of Bacillus sp R1 and RS6 were survive up to 10% NaCl concentration. All the endophytic bacteria lysed at 2% SDS. Four isolates, three belonging to genus Bacillus and one i.e . uncultured bacterium cloned exhibited growth in 0.02% sodium azide. None of the isolates were resistant to 3% potassium hydroxide and 0.01% crystal violet. In this experiment, we found that root endophytic bacteria of vegetable crop Momordica charantia belongs to genus Bacillus has maximum ability to tolerate salt stress condition. Our main objective was to isolate the endophytes depicting the PGPR traits and further to know wether such strains can offer the plant to stress tolerance capacity. Thus the strains must be itself the stress such as NaCl tolerant a characteristics to which the strain should.