Structured kinetic model to represent the utilization of multiple substrates in complex media during rifamycin B fermentation

Abstract

Industrial fermentations typically use media that are balanced with multiple substitutable substrates including complex carbon and nitrogen source. Yet, much of the modeling effort to date has mainly focused on defined media. Here, we present a structured model that accounts for growth and product formation kinetics of rifamycin B fermentation in a multi-substrate complex medium. The phenomenological model considers the organism to be an optimal strategist with an in-built mechanism that regulates the sequential and simultaneous uptake of the substrate combinations. This regulatory process is modeled by assuming that the uptake of a substrate depends on the level of a key enzyme or a set of enzymes, which may be inducible. Further, the fraction of flux through a given metabolic branch is estimated using a simple multi-variable constrained optimization. The model has the typical form of Monod equation with terms incorporating multiple limiting substrates and substrate inhibition. Several batch runs were set up with varying initial substrate concentrations to estimate the kinetic parameters for the rifamycin overproducer strain Amycolatopsis mediterranei S699. Glucose and ammonium sulfate (AMS) demonstrated significant substrate inhibition toward growth as well as product formation. The model correctly predicts the experimentally observed regulated simultaneous uptake of the substitutable substrate combinations under different fermentation conditions. The modeling results may have applications in the optimization and control of rifamycin B fermentation while the modeling strategy presented here would be applicable to other industrially important fermentations.

A cybernetic model to predict the effect of freely available nitrogen substrate on rifamycin B production in complex media

“…Furthermore, in preliminary experiment, no product formation was detected when culture was grown on S ANS as sole substrate. This reflects the significance of glucose in rifamycin B production as reported earlier (Bapat et al 2006). The low values of Ks i,j and Kp i,j for amino acids indicate that growth and product formation can take place even at very low concentration of S ANS .…”

“…Previously, we reported a structured model for rifamycin B fermentation in shake flask (Bapat et al 2006) to predict the growth of A. mediterranei S699 on a rifamycin B production. Five different S ONS are chosen.…”

“…The seed culture was grown for 72 h with a single baffled flask before transferring to the fermentation medium. The fermentation media were composed of micronutrients and glucose as reported previously (Bapat et al 2006).…”

“…The biomass was measured using pre-weighed filter papers (Whatmann, Brentford, Middlesex, UK) as previously reported (Bapat et al 2006). The concentration of free amino acids was estimated via the ninhydrin method (Moore 1968).…”

“…Further, we have proposed a model that accounts for growth and product formation kinetics of rifamycin B fermentation in a multi-substrate complex medium (Bapat et al 2006). Here, we present a cybernetic model (Kompala et al 1984;Dhurjati et al 1985;Ramkrishna et al 1997) for rifamycin B fermentation which accounts for the effect of various organic nitrogen sources on rifamycin B productivity.…”