On-line estimation of growth linked extracellular protein synthesis by pH control analysis

Abstract

[Excerpt] The study of on-line control strategies involving pH as the reference variable constitutes a field of particular interest, since it may be applied to a wide range of biotechnological systems for the production of biomass, proteins and growth-linked products (1-4). Experimental evidence of the existence of a direct relationship between growth and proton production in fermentation processes has been reported in the past (5-7) but the metabolic basis of the underlying relationships remained unclear. A formal physiological study conducted under aerobic controlled conditions has shown that the nitrogen assimilation pathway is the main net proton-contributing pathway and that there is a direct relationship between the specific nitrogen uptake rate (qN) and the specific proton production rate (qF) (8). From this knowledge specific relationships between growth (associated with nitrogen assimilation) and proton production could be derived (9). [...]