Glucose and Acetate Metabolism in E. coli – System Level Analysis and Biotechnological Applications in Protein Production Processes

Abstract

Escherichia coli is the main bacterial producer of heterologous proteins. The current production strategies aim at growing the bacteria to high density in order to achieve high levels of desired proteins. The major obstacle for reaching high cell densities with high product titers is the tendency of the bacteria to accumulate acetate during the unrestricted growth on glucose. Moreover, the high demand for precursors and energy required for the biosynthesis of the heterologous protein causes the cells to readjust their anabolic and catabolic reactions which, most often, aggravate the acetate problem. Implementing fed-batch protocols and employing more robust strains, such as E. coli B instead of K, can reduce acetate formation. Another approach is to implement metabolic engineering to minimize acetate formation by: (a) turning off genes which directly lead to the formation of acetate, (b) introducing genes that channel the carbon flow away from acetate towards other pathways, and (c) by reducing the glucose uptake through deleting or replacing genes of the sugar uptake system. Results show that a more general approach that focuses on global regulators and/or gene sets, encoding multiple pathways will be required to construct a robust strain capable of efficiently executing the production of recombinant proteins at high growth rates without the formation of toxic byproducts such as acetic acid.