Modeling and Optimization of Phosphate Solubilizing Bacteria Isolated from Rhizospheric Soils of the Coffee Plant using Artificial Neural Network (ANN) and Response Surface Methodology (RSM).

Phosphorus is often found inaccessible to plants, as it forms precipitates with cations and can be converted to accessible forms by using Phosphate solubilizing bacteria (PSB). In the present study, isolation and characterization of phosphate solubilizing bacteria from rhizospheric soil of coffee plants were performed. The influence of four independent variables (incubation temperature, incubation time, pH, and inoculum size) was investigated and optimized using an artificial neural network and response surface methodology on the solubility of phosphate and indole acetic acid production. The bacterium that can dissolve phosphate were isolated in Pikovskaya’s agar containing insoluble tricalcium phosphate. Total, six Phosphate Solubilizing Bacteria were isolated and three of them (PSB1, PSB3, and PSB4) were found to be effectively solubilizing phosphate. Based on phosphate solubilizing index results Pseudomonas bacteria (PSB1) was selected for modeling. The results showed that both models performed reasonably well, but properly trained artificial neural networks have the more powerful modeling capability compared to the response surface method. The optimum conditions were found to be incubation temperature of 37.5 oC, incubation time of 9 days, pH of 7.2, and inoculum size of 1.89 OD. Under these conditions, the model predicted solubility of phosphate of 260.69 µg/ml and production of IAA of 80.00µg/ml with a desirability value of 0.947. Generally, the isolated Pseudomonas bacteria is a promising Phosphate solubilizing capability that enhances plant growth and this research is a base for recommending the use of this bacterial strain for biofertilizer, as an alternative to synthetic fertilizer.