Plant growth-promoting capabilities of microorganisms and PCR amplification of nitrogen fixing (nif) gene in bacteria isolated from cassava plant rhizospheric soil from Ota, Ogun State, Nigeria

The application of potent bacteria and fungi as bio-fertilizer can improve the soil nitrogen status leadingto enhanced soil well-being and agricultural production. Bacteria and fungi were isolated from soilsamples collected around 20 randomly selected cassava plants obtained from Bells University farm,Ota. The isolates were screened for phosphate solubilization activity, indole acetic acid (IAA) productionand heavy metal tolerance using standard methods. Isolates were identified based on morphologicaland sequencing of the amplified 16S rRNA and ITS genes for bacteria and fungi respectively. PCRamplification of the nif gene was done using two primers. Results of the molecular identification showedthat the bacterial and fungal isolates were Pseudomonas resinovorans NOU6 (PP506413), Klebsiellavariicola NOU5 (PP506412), Kosakonia radicincitans NOU1 (PP493938) and Aspergillus assiutensisNOU2 (PP493939), Aspergillus brunneoviolaceus NOU3 (PP493940) and Aspergillus tubingensisNOU4 (PP493941) respectively. Indole acetic acid produced by bacterial and fungal isolates rangedfrom 121-147 µg/ml and 14-33 µg/ml respectively. The three fungal isolates solubilized phosphate withsolubilization index (SI) ranging from 4.25 – 6.25. Results of the heavy metal tolerance test showedthat all bacteria isolates were sensitive to mercury while they showed tolerance to tin, cobalt, chromiumand iron though at varying degrees. Only Kosakonia radicincitans strain NOU1 (C5) habours the nifgene that codes for nitrogenase enzyme. This research offers insights into the possible use of thesemicroorganisms as bio-fertilizers for crop improvement and also underscores the importance of usingmolecular techniques to target bacteria strains that possess the potentials to fix atmospheric nitrogen.