Optimizing Nutritional and Culture Medium Conditions for Potassium Release from Illite by Aspergillus niger and Pseudomonas fluorescens

Present research was carried out to evaluate the effect of different carbon sources on K release by Pseudomonas fluorescens and Aspergillus niger and modeling the effects of incubation time, pH and different amounts of carbon source on K release using central composite design. At the first step, 12 experiments were defined with a combination of different levels, and the effects of different carbon sources including glucose, sucrose and fructose at two levels of +1 (10 g.l-1) and -1 (5 g.l-1) on potassium dissolution of illite was studied. After selection of effective carbon source, different ranges of independent variables including incubation time, pH and carbon source were considered and experiment design has been made based on the coded values of them. Results showed that there is no difference between carbon sources, which were used at the first step of experiment, so each of them can be used as alternatives to each other in culture medium. According to the statistical analysis results of central composite design, pH has a positive impact on increasing the soluble potassium release (P>0.001). Maximum potassium release by bacteria and fungus, 109.75 and 170.3 mg.l-1 respectively, observed at central levels of incubation time and carbon source and pH = 10.36. Based on determination coefficient of, 91 and 87.8 percent of soluble potassium changes in the presence of bacteria and fungus can be explained by this central composite design model, respectively.