Enhancement of Pseudomonas Aeruginosa Growth and Rhamnolipid Production Using Iron-Silica Nanoparticles in Low-Cost Medium

The application of iron-silica (Fe-Si) nanoparticles for the enhancement of the Pseudomonas aeruginosa growth and rhamnolipid production in molasses medium was studied. The experiments were designed based on the response surface method (RSM) to optimize growth and rhamnolipid production. The concentration of nanoparticles and the time required to add nanoparticles to culture medium were considered as independent variables. The dry weight of cell, the dry weight of rhamnolipid and the surface tension were measured as response variables. In addition, to determine a basic and low-cost medium, the concentrations of molasses and NaCl as components of medium were optimized by RSM. The optimum medium was estimated to include 15% of molasses without NaCl. The results showed that the highest increase in the growth of P. aeruginosa is 25% which occurred at 600 mg/L of nanoparticles and 18 h of addition time compared to the free-nanoparticles experiment. In the same way, the highest increase in rhamnolipid production was 57% at 1 mg/L of nanoparticles and 6 h of addition time compared to blank experiment. TEM images of the morphology changes of bacteria demonstrated the permeation of nanoparticles into the inbound cells. Results of this study reveal the great potential of Fe-Si nanoparticles to overcome the difficulties of the rhamnolipid production in industrial scale.