title: Oxygen supply in Bacillus thuringiensis fermentations: bringing new insights on their impact on sporulation and δ-endotoxin production.
abstract: The growth kinetics, sporulation, and toxicity of Bacillus thuringiensis var. israelensis were evaluated through the analysis of batch cultures with different dissolved oxygen (DO) profiles. Firstly, DO was maintained constant at 5%, 20%, or 50% throughout fermentation in order to identify the most suitable one to improve the main process parameters. Higher biomass concentration, cell productivity, and cell yield based on glucose were obtained with 50% DO. The higher aeration level also resulted in higher spore counts and markedly improved the toxic activity of the fermentation broth, which was 9-fold greater than that obtained with 5% DO (LC(50) of 39 and 329 mg/L, respectively). Subsequently, using a two-stage oxygen supply strategy, DO was kept at 50% during the vegetative and transition phases until the maximum cell concentration was achieved. Then, DO was changed to 0%, 5%, 20%, or 100% throughout sporulation and cell lysis phases. The interruption of oxygen supply strongly reduced the spore production and thoroughly repressed the toxin synthesis. On the contrary, when DO was raised to 100% of saturation, toxic activity increased approximately four times (LC(50) of 8.2 mg/L) in comparison with the mean values reached with lower DO levels, even though spore counts were lower than that from the 50% DO assay. When pure oxygen was used instead of normal air, it was possible to obtain 70% of the total biomass concentration achieved in the air assays; however, cultures did not sporulate and the toxin synthesis was consequently suppressed.
authors.affiliation: Laboratório de Biotecnologia, Universidade Estadual do Norte Fluminense Darcy Ribeiro, CEP 28013-602, Campos dos Goytacazes, RJ, Brazil.
authors.forename: Fabrízio Siqueira
authors.initials: FS
authors.lastname: Boniolo
authors.forename: Raphael Cardoso
authors.initials: RC
authors.lastname: Rodrigues
authors.forename: Arnaldo Márcio Ramalho
authors.initials: AM
authors.lastname: Prata
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: López
authors.forename: Tânia
authors.initials: T
authors.lastname: Jacinto
authors.forename: Mauricio Moura
authors.initials: MM
authors.lastname: da Silveira
authors.forename: Marília Amorim
authors.initials: MA
authors.lastname: Berbert-Molina
mesh_terms: D001413:Bacillus thuringiensis / Q000254:growth & development* / Q000378:metabolism*; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000096:biosynthesis*; D018533:Biomass; D003470:Culture Media / Q000737:chemistry; D004731:Endotoxins / Q000096:biosynthesis*; D005285:Fermentation; D006460:Hemolysin Proteins / Q000096:biosynthesis*; D010100:Oxygen / Q000378:metabolism*; D013171:Spores, Bacterial / Q000254:growth & development*
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D003470:Culture Media; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis; D010100:Oxygen