Isolation of Azospirillum spp and Evaluation of its Plant Growth Promoting Abilities

Abstract

Background: This study aimed to isolate Azospirillum species from the soil environment and assess their plant growth-promoting abilities. Soil samples were collected from 10 different agricultural sites. The bacteria were isolated by serially diluting the soil samples and each aliquot was transferred into a Nitrogen-free bromothymol blue medium and then incubated for 7 days at 37°C. The isolates were further screened based on their morphological, biochemical and plant growth phytohormone production. The Fourier Transform Infrared Spectrophotometer will be used to elucidate the functional groups present in the isolates. Furthermore, the isolates were subjected to molecular identification. The results showed that Seventeen (17) bacteria were isolated from the soil samples of different crop plants using nitrogen-free bromothymol blue medium with all forming a white subsurface pellicle and they were further screened to seven (7) isolates, based on their morphological, biochemical, and plant growth phytohormones production characteristics, they include A1, A2, A3, A4, A5, A6 and A7. Three of the isolates (A1, A3, and A6) were randomly selected for molecular identification. The Fourier Transform Infrared Spectrophotometer identified the functional groups that are present in the Azospirillum strains to be aromatic compounds. All isolates showed ammonium production potential with A7 having the highest production of 781.3 µg/ml. Only four (4) isolates showed the ability to solubilize Calcium triphosphate with A7 having the highest solubilization (776 µg/ml). Furthermore, all isolates exhibited the ability to produce Indole acetic acids in the growth medium with A6 having the highest production (798.5 µg/ml). The molecular analysis and the sequence analysis of the three isolates 16SrRNA showed two of the isolates to be Azospirillum brasilense (A1, A3) and the other Azospirillum lipoferum (A6). Therefore, this study shows that this strain of Azospirillum has a high ability to produce Indole Acetic Acids, which aids in the production of phytohormones such as Auxins, Solubilize Calcium triphosphate and hence proffer a sustainable solution to improving plant growth.