Characterization and Plant Growth Promoting Properties of a Bacillus sp. Isolated from Maize Roots

Abstract

Aim: To isolate plant growth promoting Bacillus strains from maize roots and to characterize using molecular methods, the strain with greatest potential for plant growth promotion.
 Place and Duration of Study: Department of Applied Microbiology and Brewing, Nnamdi Azikiwe University, Awka, between February 2019 and March 2020.
 Methodology: The isolation of plant growth promoting rhizobacteria (PGPR) from maize roots was made using Nitrogen Free Bromothymol Blue (NFB) broth. They were screened for Phosphate solubilizing activities on Pikovskaya (PVK) agar. Quantitative determination and solubilization of different types of Phosphates was carried out using Pikovskaya broth. Optimization of factors affecting phosphate such as NaCl concentration, initial pH of the medium, size of inoculum, was done using pvk broth. Evaluation of other plant growth promoting properties were carried out such as IAA, Ammonia, cellulase and HCN production. 
 Results: Eleven Nitrogen fixing bacteria were isolated using NFB broth based on colour change of the medium from green to blue. Test for phosphate solubilization abilities of the organisms revealed that nine of the isolates solubilized phosphate on PVK agar. Organism coded with IS52 gave the least solubilization index of 1.14 while isolate IS19 gave the highest index of 3.4. Isolate IS19 yielded the highest amount of 73.5µg/ml P, while isolate IS30 was the weakest solubilizer in PVK broth, yielding 19.4µg/ml P. The best isolate IS19, produced the plant growth hormone Indole Acetic acid at a concentration of 105.4μg/ml. The organism also gave a positive result for ammonia and cellulase production but did not produce Hydrogen cyanide. It was identified as Bacillus subtilis using the 16S rRNA gene sequencing.
 Conclusion: Bacillus subtilis fixed Nitrogen qualitatively and solubilized insoluble phosphates in addition to other plant growth promoting properties, thus Bacillus subtilis has potential for plant growth promotion, making it an efficient strain for biofertilizer production