title: Phase-specific optimization of multiple endotoxin-protein production with genetically engineered Bacillus thuringiensis.
abstract: An optimization approach was designed to specifically study the toxin-expression phase of the fermentation process of a genetically engineered Bacillus thuringiensis strain expressing dual toxin proteins (CryI and CryIII). The study has resulted in the discovery of important nutrient and process factors affecting toxin-protein yield. The results show that the existence of nitrogen sources in the medium during the toxin-expression phase is detrimental to the toxin-protein expression, while a high carbon-source level (40 g/l) encouraged protein expression. The study also suggests that the depletion of nitrogen source is the trigger for B. thuringiensis to initiate sporulation and toxin expression. A temperature setting of 28 degrees C for B. thuringiensis fermentation processes is optimal for protein yield, and reduces the oxygen requirement. It was found that the optimal conditions for spore yield and for toxin-protein yield were not the same, even though sporulation and toxin formation proceed simultaneously during the fermentation process. Scale-up studies were also conducted to confirm the optimal conditions obtained from a small-scale optimization study.
authors.affiliation: Department of Chemistry and Biochemical Engineering, Rutgers University, Piscataway, NJ, USA.
authors.forename: X M
authors.initials: XM
authors.lastname: Yang
authors.forename: S S
authors.initials: SS
authors.lastname: Wang
mesh_terms: D001413:Bacillus thuringiensis / Q000235:genetics* / Q000378:metabolism; D001709:Biotechnology / Q000379:methods; D004731:Endotoxins / Q000235:genetics* / Q000378:metabolism*; D005285:Fermentation; D005818:Genetic Engineering / Q000379:methods; D005947:Glucose / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics* / Q000378:metabolism; D012492:Salts; D013171:Spores, Bacterial; D013696:Temperature
chemical_list: D004731:Endotoxins; D011994:Recombinant Proteins; D012492:Salts; D005947:Glucose