Effect of Optimization Factors on the Production of Bacillus subtilis and Escherichia coli Synthesized Silver Nanoparticles

The recent discovery of silver nanoparticles and their production from Bacillus subtilis and Escherichia coli have enhanced optimization attempts. Extracellular biosynthesis of silver nanoparticles using the Bacillus subtilis and Escherichia coli cultured supernatants was done according to standard procedures. Optimization of the production of silver nanoparticles was done in a 3 X 3 (three factors) design involving temperature (25, 30 and 35 degrees), pH (6, 7 and 8), and time of incubation (24, 48 and 72 Hours) in a total of 15 non-randomized runs. The result showed a sharp decline in the synthesis of B. subtilis silver nanoparticles (BNP) within the first 40 hours but attained steady optimization between 40 – 60 mins. An exponential increase in BNP synthesis was observed between pH 6 – 7 with a slight decline observed between pH 7 – 8. An increase in temperature from 25-300C resulted in a decrease in the production of BNP while the production of BNP increased over 30-350C. An initial lag in Escherichia coli synthesized silver nanoparticle (ENP) synthesis was observed with temperature variations. ENP synthesis maintained an exponential increase up to pH 7 but decreased with 7>pH≤8. The results showed that the increase in temperature resulted in a gradual decrease in production of ENP producing a negative slope. Therefore, the variations in optimization factors of silver nanoparticles produced from both B. subtilis and E. coli led to improved production.