Existence of a scaling relation in continuous cultures of Scheffersomyces stipitis: the steady states are completely determined by the ratio of carbon and oxygen uptake rates

• Main Authors: Shraddha Maitra, Atul Narang
• Format: Article
• Language: English
• Published: BMC 2019-01-01
• Series: Biotechnology for Biofuels
• Subjects: Parametric sensitivity of ethanol production; Carbon limitation; Oxygen limitation; Dual limitation; Scheffersomyces (Pichia) stipitis
• Online Access: http://link.springer.com/article/10.1186/s13068-019-1357-3

Abstract Background Recently, we showed that steady-state continuous cultures of S. stipitis follow the principles of growth on mixture of two complementary substrates. More precisely, when such cultures are fed with progressively higher concentrations of glucose s f at fixed dilution rate D = 0.1 h−1, oxygen mass-transfer coefficient k l a = 50 h−1, and oxygen solubility $$c_{\text{o}}^{*}$$ co∗ , they transition from glucose- to oxygen-limited growth through an intermediate dual-limited regime in which both glucose and oxygen are limiting, and ethanol is produced without loss of glucose. It is, therefore, of considerable interest to characterize the dual-limited regime. We found that the dual-limited regime occurs precisely when the operating parameters D, s f, k l a, and $$c_{\text{o}}^{*}$$ co∗ satisfy the relation $$Y_{\text{os}} < Ds_{\text{f}} /\left( {k_{\text{l}} a \cdot c_{\text{o}}^{*} } \right) < Y_{\text{os}}^{\prime }$$ Yos<Dsf/kla·co∗<Yos′ , where Y os and $$Y_{\text{os}}^{\prime }$$ Yos′ denote g of glucose consumed per g of oxygen consumed in the carbon- and oxygen-limited regimes. In this work, our goal was to determine if the above characterization of the dual-limited regime holds over a wider range of D, k l a, and to understand why the dual-limited regime is determined by the dimensionless ratio $$Ds_{\text{f}} /\left( {k_{\text{l}} a \cdot c_{\text{o}}^{*} } \right)$$ Dsf/kla·co∗ . Results To this end, we performed the foregoing experiments at three additional dilution rates (D = 0.07, 0.15, and 0.20 h−1) and one additional mass-transfer coefficient (k l a = 100 h−1). We find that the above characterization of the dual-limited regime is valid for these conditions as well. Furthermore, the boundaries of the dual-limited regime are determined by the dimensionless ratio $$Ds_{\text{f}} /\left( {k_{\text{l}} a \cdot c_{\text{o}}^{*} } \right)$$ Dsf/kla·co∗ , because the steady-state concentrations are completely determined by this ratio. More precisely, if the steady-state concentrations of biomass, glucose, oxygen, and ethanol are suitably scaled, they collapse into a single curve with $$Ds_{\text{f}} /\left( {k_{\text{l}} a \cdot c_{\text{o}}^{*} } \right)$$ Dsf/kla·co∗ as the independent variable. Conclusion The dual-limited regime is characterized by the relation $$Y_{\text{os}} < Ds_{\text{f}} /\left( {k_{\text{l}} a \cdot c_{\text{o}}^{*} } \right) < Y_{\text{os}}^{{\prime }}$$ Yos<Dsf/kla·co∗<Yos′ over the entire range of operating condition 0.07 h−1 ≤ D ≤ 0.20 h−1 and $$50 \;{\text{h}}^{ - 1} \le k_{\text{l}} a \le 100\;{\text{h}}^{ - 1}$$ 50h-1≤kla≤100h-1 . Since the effect of all operating parameters is embedded in the single parameter $$Ds_{\text{f}} /\left( {k_{\text{l}} a \cdot c_{\text{o}}^{*} } \right)$$ Dsf/kla·co∗ , the dimensionless plot provides a powerful tool to compare, with only a handful of data, various ethanol-producing strains over a wide range of operating conditions.