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

Abstract

 The application of potent bacteria and fungi as bio-fertilizer can improve the soil nitrogen status leading
to enhanced soil well-being and agricultural production. Bacteria and fungi were isolated from soil
samples 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) production
and heavy metal tolerance using standard methods. Isolates were identified based on morphological
and sequencing of the amplified 16S rRNA and ITS genes for bacteria and fungi respectively. PCR
amplification of the nif gene was done using two primers. Results of the molecular identification showed
that the bacterial and fungal isolates were Pseudomonas resinovorans NOU6 (PP506413), Klebsiella
variicola NOU5 (PP506412), Kosakonia radicincitans NOU1 (PP493938) and Aspergillus assiutensis
NOU2 (PP493939), Aspergillus brunneoviolaceus NOU3 (PP493940) and Aspergillus tubingensis
NOU4 (PP493941) respectively. Indole acetic acid produced by bacterial and fungal isolates ranged
from 121-147 µg/ml and 14-33 µg/ml respectively. The three fungal isolates solubilized phosphate with
solubilization index (SI) ranging from 4.25 – 6.25. Results of the heavy metal tolerance test showed
that all bacteria isolates were sensitive to mercury while they showed tolerance to tin, cobalt, chromium
and iron though at varying degrees. Only Kosakonia radicincitans strain NOU1 (C5) habours the nif
gene that codes for nitrogenase enzyme. This research offers insights into the possible use of these
microorganisms as bio-fertilizers for crop improvement and also underscores the importance of using
molecular techniques to target bacteria strains that possess the potentials to fix atmospheric nitrogen.