Genetic polymorphism of prevalent root nodules bacterial strain from Bambara nut

Abstract

Bambara groundnut is an underutilized crop of good microbial resources in green manure. The knowledge of the true microbial diversity in rhizopheric bacteria of Bambara groundnut is fundamental to effective exploitation of these bacteria. This study employed morphological, biochemical as well as molecular approach in the isolation, identification and characterization of these bacteria. Morphological and biochemical analysis revealed only 8 out of 30 rhizopheric bacteria isolated from the Bambara root nodules as potential nitrogen fixing bacteria. These were further analyzed using the 16S rDNA and PCR-RFLP. The 16S rDNA sequences utilized in phylogenetic tree showed that 4 of the strains NWU A3 (Enterococcus durans) , NWU A8 (Bacillus pumilus) NWU A 7 (Acinetobacter johnsonii) and NWU A 10 (Acinetobacter johnsonii) possessed 99% similarity index with the reference strains while 4 strains did not cluster with any of the reference strain due to their distinct nucleotide signature from the existing one. These strains are: NWU A2 (Fictibacillus nanhaiensis), NWU AS (Bacillus pumilus), NWU A6 (Fictibacillus arsenicus), and NWU A9 (Acinetobacter johnsonii). The PCR-RFLP expressed fingerprints of the strains generated by the ribosomal genes in three distinguished patterns of different combinations, representing three distinct l 6S rRNA genotypes among all the strains. Gene responsible for nodulation and nitrogen fixation in these strains are borne on their plasmid, which is an indication of probable horizontal gene transfer. In a nutshell, the rhizopheric bacteria found in the root nodules of Bambara groundnut can be used as biofertilizer in the future as main microbial resource, considering its rich bacterial diversity. This biological nitrogen fixation technology could be a right substitute to commercially available N fertilizer which are less environmentally friendly. In future research, three diverse group of rhizobia expressed from the PCR-RFLP point of view can further be analyzed and characterized through high throughput molecular technique to choose the ideal strain of rhizobia for Bambara.