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

Abstract

The sporulation and toxicity of Bacillus thuringiensis H14 were studied as a function of aeration. The fed-batch cultures carried out in the similar aeration conditions were followed in four different oxygen transfer rates containing 0, 20, 100 and 250 mmol/l/h. The percentage of total cells which had formed refractile spores in these four oxygen transfer rates were 100, 93, 84 and 48%, respectively. The highest rate of sporulation was observed in the absence of oxygen and the mature spores were the only population present under this condition at the end of culture. Sporulation in a large portion of cells failed under saturated oxygenation and either mature spores or vegetative cells were present at the end of culture. In the intermediate conditions, cells in different physiological states could be observed at the end of culture. It was found that the optimal conditions for spore yield and for d-endotoxin yield were not the same, even though sporulation and d-endotoxin formation proceed simultaneously during the fermentation process. The 130-kDa d-endotoxin seemed to be more sensitive to aeration conditions. The higher toxicity against Culex pipiens was obtained under the saturated condition.

Oxygen supply in Bacillus thuringiensis fermentations: bringing new insights on their impact on sporulation and δ-endotoxin production

“…The highest DO concentration (100%) had a strong negative impact on spore production, but toxic activity increased by four times in comparison with values reached with lower DO levels (5%, 20%, or 50%) during phases III and IV (Table 2). These results are in agreement with the reports given by Sarrafzadeh and Navarro (2006), who found lower spore counts and higher toxicity when the sporulation phase of Bti cultures were carried out under saturated oxygen condition. The authors also report that in such a situation mature spores and vegetative cells were the only two populations present at the end of culture, meaning that immature spores were completely absent, a finding also observed here.…”

“…By applying an identical approach, Avignone-Rossa et al (1992) obtained spore counts similar to those reached in non-limited cultures; however, toxin production was not thoroughly suppressed. Sarrafzadeh and Navarro (2006) found that the interruption of air supply in the course of the fermentation led to a total sporulation of the culture and slightly lower toxicity than that observed in non-limiting conditions. However, the aeration was interrupted after 24 h of fed-batch cultures performed without oxygen limitation, when a considerable portion (40%) of the population had already started sporulation.…”

“…In order to evaluate the impact of aeration conditions on sporulation, as an isolated phase of Bti fermentation, Sarrafzadeh and Navarro (2006) performed fed-batch cultures under constant DO concentration of 20% for 24 h, and sustained them in batch mode for additionally 24 h at different OTR. The highest sporulation rate (100%) was observed in the absence of oxygen, while the lowest rate (48%) occurred with saturated oxygenation, the results with intermediate OTR being closer to those achieved using interrupted aeration.…”

Effects of oxygen volumetric mass transfer coefficient on transglutaminase production by Bacillus circulans BL32

“…may be induced by the absence of oxygen [28][29][30]. However, cultures of this bacterium under anoxic conditions will halt biomass formation and affect negatively TGase production, as it has been demonstrated by one experiment run by us at 400 rpm and 0 vvm air (0% dissolved oxygen concentration, results not shown).…”

Solid-State Fermentation for the Concomitant Production of δ-Endotoxin and Endospore from <i>Bacillus thuringiensis</i> subsp. <i>kurstaki</i>

“…The toxicity (due to δ-endotoxin and endospore) was about four times higher under non-aerated conditions [27]. Sarrafzadeh and Navarro [28] observed the highest concentration of spores being 100% mature under anaerobic conditions for Bt strain H14. Das and Danker [29] showed that anoxic and water stresses favoured production of spores and crystals at an early stage of growth.…”