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Influence of pH Control Agents on Entomotoxicity Potency of Bacillus thuringiensis using Different Raw Materials
Authors:Abdessalem Yezza  Rajeshwar D Tyagi  José R Valéro  Rao Y Surampalli
Institution:(1) Terre et Environnement, INRS Eau, 490, Rue de la Couronne, G1K 9A9 Québec, Canada;(2) Centre Foresterie des Laurentides, Service Canadien des Forêts, Canada;(3) US Environmental Protection Agency , USA
Abstract: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.
Keywords:Bacillus thuringiensis  entomotoxicity  pH control  protease activity  sporulation  wastewater sludge
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