Kinetic analysis and mathematical modeling of cell growth and canthaxanthin biosynthesis by Dietzia natronolimnaea HS-1 on waste molasses hydrolysate

Abstract

A kinetics study on the canthaxanthin (CTX) production by the bacterium Dietzia natronolimnaea HS-1 grown in a batch bioreactor using enzymatic hydrolyzed molasses (EHM, 5–50 g l⁻¹) as the carbon substrate was developed. After the preliminary studies, the eight models of Aiba, Andrews and Noack, Edward, Haldane, Monod, Moser, Teissier and Webb were used to describe the substrate inhibition effect and specific growth rate. Contrary to Monod's, Webb's model presented a good fit to the growth kinetics data (R² = 0.9833). The kinetic constants of the Webb equation were μ_m = 0.07042 h⁻¹, K_s = 13.26 g l⁻¹ and K_i = 6.631 g l⁻¹. Experimentally, it was observed that EHM was an inhibitory-type substrate and the inhibition effect of EHM became predominant above a concentration of 25 g l⁻¹. The Luedeking–Piret model was successfully used to describe CTX formation and substrate consumption according to the growth characteristics of D. natronolimnaea HS-1. The values of two key kinetic constants, namely the growth (α) and non-growth (β) associated constants for CTX production at the optimal concentration of EHM (25 g l⁻¹) were 1.163 g g⁻¹ and 0.021 g g⁻¹ h⁻¹, respectively. The models introduced here can be practical tools for the design and control of cultures of this bacterium, and could allow for improvements in the yield of the CTX production process.