Modeling growth and succinoglucan production by Agrobacterium radiobacter NCIB 9042 in batch cultures

Abstract

Wild‐type Agrobacterium radiobacter NCIB 9042 has been cultivated in batch cultures on a synthetic medium which was adapted for growth and succinoglucan production. Experiments were carried out in a 4‐L stirred‐tank aerated reactor. Glucose, biomass, polysaccharide, protein, and inorganic‐ and organic‐nitrogen concentrations were measured, and oxygen consumption and CO₂ production rates were obtained by a gas‐balance technique. Nitrogen balance shows that inorganic nitrogen is entirely recovered into proteins. The carbon balance is satisfied with in ±5%. Stoichiometric equations for biomass growth and succinoglucan synthesis were established. The biosyntheticpolymer pathways including ATP and cofactor consumption were investigated. From previous studies, a (P/O) value of 1.66 is selected for oxygen sufficient cultures. The actual ATP requirements of 25.4 mmol ATP/g succinoglucan (38.5 mol ATP/mol succinoglucan), determined by a metabolic analysis, is 2.39 times the stoichiometric value. Experimental results were modeled by a system of differential equations. The exponential growth phase was described by a nitrogen‐limited Monod equation. Subsequent succinoglucan synthesis followed a slightly modified Luedeking–Piret relation partitioning internal and external polysaccharide. Experimentally determined coefficients are compared with published results for continuous culture of A. radiobacter NCIB 11883.