Bioprospecting of endophytic bacteria from nodules and roots of Vigna radiata, Vigna unguiculata and Cajanus cajan for their potential use as bioinoculants

Abstract The haphazard and unwarranted use of chemical fertilizers has disturbed the soil microflora and groundwater by rendering them highly contaminated and reduced its agricultural productivity considerably. To revive the soil, groundwater and to restore the fertility of soil, a novel approach of using bioinoculants to restore both soil microflora and groundwater-detox with an added bonus of organic agriculture, is the major requirement at this moment. This study is dedicated towards isolation and characterization of the plant growth promoting endophytic bacteria (PGPEB) from the leguminous crops viz. Vigna radiata, V. unguiculata and Cajanus cajan. A total of 367 endophytic bacteria were isolated and characterized for plant growth promoting (PGP) attributes. Out of total, 97 endophytic bacteria were selected based upon morphological distinctness and plant growth promoting attributes. On the basis of amplified ribosomal DNA restriction analysis (ARDRA), these isolates were grouped into 45 genotypes. These genotypes were further evaluated for their PGP attributes and 28 representative strains selected for 16S rDNA sequence identification. The NCBI database analysis revealed the maximum identity of these genotypes towards different genera of three major phyla i.e. Firmicutes, Gamma (γ)-Proteobacteria and Actinobacteria. Firmicutes exclusively represented by 80% of isolates, encompassed three different genera Bacillus (10 species), Brevibacillus (2 species) and Lysinibacillus (1 species). The two genera included in γ-Proteobacteria were assigned to Enterobacter and Pseudomonas and two genera viz. Microbacterium (2 species) and Kocuria (1 species) to phylum Actinobacteria. B. panacihumi NMP3, B. australimaris NMP6, B. zhangzhouensis NMP7, M. barkeri NMP12, L. pakistanensis NAP3 and K. marina NAP9 are documented for the first time as PGPEB from these crops to the best of our knowledge. The analysis of in vivo pot experiment revealed that isolates E. cloacae NMP10, M. barkeri NMP12, B. licheniformis MHN12, B. paralicheniformis NMP13, M. arborescens NMP8, B. australimaris NMP6, P. stutzeri NAP4, B. megaterium NAP1, B. aerius NAP6 and B. megaterium NAP10 from V. radiata and C. cajan significantly increased all the growth parameters of their respective crops. Thus the study underlines the potential of these isolates to be harnessed as commercial bio-inoculants for integrated crop yield improvement.