The effect of oxygen on the sporulation, δ-endotoxin synthesis and toxicity of Bacillus thuringiensis H14

Modeling of Fermentation Process of Bacillus Thuringiensis as a Sporulating Bacterium

This paper intended to develop a model for predicting the progress in sporulation of Bacillus thuringiensis as an industrially important sporulating bacterium. Three distinct forms of B. thuringiensis can be observed during the fermentation process: vegetative cells, sporangia and mature spores. A mathematical model was developed for estimating the population of these three cell forms of this bacterium. A cell population balance was derived to represent the dynamic behavior of the fermentation process in a fed-batch culture. An unstructured and segregated model was used for this purpose. Experimental data at various oxygen saturation levels (0, 50 and 100 %) were used for validating the model. The model consists of a partial differential equation that describes the distribution of the cell population based on the cell age. This equation was solved by the method of lines in MATLAB. The proposed model can properly describe the cell populations and sporulation development in the mentioned conditions.

Aeration effects on metabolic events during sporulation of Bacillus thuringiensis

The metabolism of Bacillus thuringiensis during its sporulation process was investigated under different concentrations of oxygen. At the beginning of sporulation, the aeration conditions were regulated to obtain different oxygen transfer rates (OTR) in four separate fermentations, representing interrupted, limited, non-limited, and saturated oxygenation, respectively. A higher OTR resulted in a higher pH, up to about 9 in the case of saturated oxygenation, while the interrupted oxygenation resulted in a significantly acidic culture. In contrast, the absence of oxygen resulted in rapid sporangia lysis and caused acidification of the medium, indicating a distinctly different sporangia composition and different metabolism. The bacterium also showed different CO2 production rates during sporulation, although a maximum point was observed in every case.With a higher OTR, the maximal value was observed after a longer time and at a lower value (40, 26, and 13 mmol/L/h for limited, non-limited, and saturated cases, respectively). Despite the exhaustion of glucose prior to the sporulation phase, the interrupted oxygenation resulted in acetate, lactate, and citrate in the medium with a maximum concentration of 4.8, 1.3, and 5.0 g/L, respectively. Notwithstanding, while the metabolic events differed visibly in the absence of oxygen, once sporulation was triggered, it was completed, even in the case of an interrupted oxygen supply.

Life-cycle kinetic model for endospore-forming bacteria, including germination and sporulation

We develop a mechanistic life-cycle model for endospore-forming bacteria (EFB) and test the model with experiments with a Bacillus mixed culture. The model integrates and quantifies how sporulation and germination are triggered by depletion or presence of a limiting substrate, while both substrates affect the rate of vegetative growth by a multiplicative model. Kinetic experiments show the accumulation of small spherical spores after the triggering substrate is depleted, substantially more rapid decay during sporulation than for normal decay of vegetative cells, and a higher specific substrate utilization rate for the germinating cells than that for growth of vegetative cells. Model simulations capture all of these experimental trends. According to model predictions, when a batch reactor is started, seeding with EFB spores instead of active EFB delays the onset of rapid chemical oxygen demand (COD) utilization and biomass growth, but the end points are the same. Simulated results with low aeration intensity show that germination can consume some substrate without dissolved oxygen (DO) depletion.