The concept of multiple-nutrient-limited growth of microorganisms and someof its possible applications in biotechnology processes

Justus von Liebig's 'Law of the minimum' states that usually one nutrient r estricts the maximum quantity of biomass that can be produced within a syst em where all other nutrients are available in excess. This general rule has been applied also to the growth of microorganisms, e.g., by adjusting the relative concentrations of the individual nutrients in growth media such th at one of them, in the case of heterotrophic microbes usually the carbon so urce, determines the maximum cell density that can be obtained in a culture . However, recent experimental data from chemostats have demonstrated that growth of microbial cultures can be limited simultaneously by two or more n utrients. The experimental evidence supporting the limitation of growth by multiple nutrients is reviewed here, and a concept is presented that allows predicting the zones where multiple-nutrient-limited growth occurs. The in formation so far available indicates that multiple-nutrient-limited growth conditions allow to force cells into a physiological status that cannot be achieved under traditional single-nutrient-limited growth conditions. Two e xamples are given which demonstrate that cultivation of microbial cells und er multiple-nutrient-limited growth conditions can be used to enhance the p roductivity of biotechnological processes.