Kinetics of Bacillus thuringiensis var. israelensis growth on high glucose concentrations

Abstract

The kinetic and general growth features of Bacillus thuringiensis var. israelensis were evaluated. Initial glucose concentration (S0) in fermentation media varied from 10 to 152 g/l. The results afforded to characterize four morphologically and physiologically well-defined culture phases, independent of S0 values: Phase I, vegetative growth; Phase II, transition to sporulation; Phase III, sporulation; and Phase IV, spores maturation and cell lysis. Important process parameters were also determined. The maximum specific growth rates (microX,m) were not affected with S0 up to 75 g/l (1.0-1.1 per hour), but higher glucose concentrations resulted in growth inhibition by substrate, revealed by a reduction in microX,m values. These higher S0 values led to longer Phases III and IV and delayed sporulation. Similar biomass concentrations (Xm=15.2-15.9 g/l) were achieved with S0 over 30.8 g/l, with increasing residual substrate, suggesting a limitation in some other nutrients and the use of glucose to form other metabolites. In this case, with S0 from 30.8 to 152 g/l, cell yield (YX/S) decreased from 0.58 to 0.41 g/g. On the other hand, with S0=10 g/l growth was limited by substrate, and YX/S has shown its maximum value (0.83 g/g).

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

“…As can be observed (Table 1; Fig. 1), in neither case total glucose consumption took place during cellular growth (phases I and II), probably due to the depletion of yeast extract in fermentation broth, as previously demonstrated (Berbert-Molina et al 2008). The highest Y x/s value (0.53 g/g) was obtained with 50% DO.…”

“…Earlier works demonstrated that in Bt cultures oxygen uptake rates are very high during the vegetative growth, falling drastically after the beginning of the transition phase and maintaining a decreasing profile until the end (Rowe et al 2003;Yezza et al 2005;Berbert-Molina et al 2008;Amicarelli et al 2010). Indeed, some authors verified that lower aeration rates in the sporulation phase, in relation to those employed in the earlier stages of growth, led to a greater toxicity in Btk cultures (Ghribi et al 2007a).…”

“…In a previous work (Berbert-Molina et al 2008), we proposed the division of the cell growth of B. thuringiensis var. israelensis (Bti) in four distinct phases, based on morphological and physiological changes observed in batch fermentations carried out under different glucose concentrations and unlimited oxygen supply (DO≥35% saturation).…”

“…1). Bt cultures have maximal oxygen demand during vegetative to transient growth phases (Rowe et al 2003;Berbert-Molina et al 2008) and higher oxygen uptake rates (OUR) are observed with higher DO (Avignone-Rossa et al 1992;Kraemer-Schafhalter and Moser 1996). The …”

“…Values in the same row that are not preceded by the same upper case letters are significantly different (p<0.05). t Xm time to achieve the maximum cell concentration; t f fermentation time; X m maximum cell concentration; ΔS Xm glucose consumption until t Xm ; Y x/s biomass yield based on glucose, calculated at t Xm ; p x cell productivity, calculated at t Xm ; μ m maximum specific growth rate; LC 50 lethal concentration inducing 50% mortality; ND not detected *The first value represents DO at phases I and II and the second value represents DO at phases III and IV maximum OUR value coincides with the start of cell aggregation, which is precisely the event that marks the end of phase I (Berbert-Molina et al 2008). As this event occurred later in the 50% DO assay, the strong respiratory metabolism was extended for a longer period, allowing better utilization of nitrogen sources from yeast extract.…”