Bioprocess optimization of potassium solubilization by a Bacillus isolate using response surface methodology and laboratory-scale bioreactor evaluation

Potassium-solubilizing bacteria (KSB) offer a microbial approach for mobilizing mineral bound potassium and may contribute to more sustainable nutrient management. This study aimed to isolate efficient KSB from different soil environments and optimize culture conditions for improved bacterial growth, followed by evaluation at laboratory bioreactor scale. Twenty soil samples collected from agricultural and mineral rich sited yielded 119 bacterial isolates, of which 21 exhibited potassium-solubilizing activity on Aleksandrov medium. The most promising isolated was characterized using morphological, biochemical and partial 16 S rRNA sequence analysis and showed a close relationship with Bacillus cereus. Carbon and nitrogen source screening identified glucose and yeast extract as suitable nutritional components for supporting bacterial growth. A central composite design coupled with response surface methodology was subsequently employed to investigate the effects of substrate concentration, incubation period, temperature, pH and agitation rate. The developed model showed a strong fit to the experimental data (R 2 = 0.961; adjusted R 2 = 0.899). Optimized conditions were identified at 0.3% substrate, 96 h incubation, 40 °C, pH 7.0 and 160 rpm, under which an experimental response of 1.76 (O.D 600 ) was obtained compared with the model predicted value of 1.55(O.D 600 ). Laboratory scale bioreactor evaluation further demonstrated process performance under controlled cultivation conditions, with the highest response observed at 168 h, 300 rpm, and 2 vvm. These findings demonstrate the potential of the selected potassium-solubilizing Bacillus isolate for further development and validation in microbial systems.