Influence of pH Control Agents on Entomotoxicity Potency of Bacillus thuringiensis using Different Raw Materials

Summary

In this investigation, ammonium hydroxide and acetic acid were used as pH control agents during Bacillus thuringiensis (Bt) fermentation in a pilot scale fermentor (150-l) employing two secondary wastewater sludges from two different wastewater treatment plants (CUQS and JQS) and semi-synthetic soybean meal medium as raw materials. Regardless of the cultivation medium, a substantial increase in total cell count, spore count, protease activity and entomotoxicity was achieved when the pH of the culture was controlled using NH₄OH/CH₃COOH. At harvest, total cell count increased by almost 17%, 33% and 25%; protease activity was enhanced by 12%, 33% and 53% and maximal spore count augmented by almost 28%, 48% and 33% in CUQS, JQS and soybean medium, respectively. Entomotoxicity potency was improved by 22%, 21% and 14% in CUQS, JQS and soybean medium, respectively compared to results obtained with NaOH/H₂SO₄ as pH control agents. A higher entomotoxicity was also observed using sludge compared to the soybean medium. This improvement of the Bt process performance was a consequence of the addition of rapidly utilizable carbon and nitrogen source through pH control, which stimulated endotoxin production in the crystal and enhanced sporulation.