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 amaximum 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.