(519e) Toward A Cellulolytic Escherichia Coli

Production of energy, chemicals, and materials from renewable sources such as cellulose can address the impending energy crisis, shortage of chemical raw material (petroleum), and environmental issues associated with the use of fossil fuel. Although E. coli is the preferred microorganism for constructing biotechnology based production systems for useful products, wild type E. coli is not able to use cellulose directly. Pre-fermentation cellulose hydrolysis is necessary, which adds complexity and cost to a bioprocess.

Engineering a cellulolytic E. coli is challenging due to the inability of the organism to secrete heterologous enzymes. Through modification of cellular membrane permeability, we have developed a novel method that enables extracellular production of heterologous enzymes. CelA from Clostridium thermocellum, encoding an exoglucanase, was cloned and overexpressed in E. coli. About 70% of the enzyme activity was found in the extracellular medium. A batch cultivation in a fermenter led to an extracellular cellulase titer of 700 U/L, significantly (4-5 fold) higher than the control.

In this presentation, we will detail the molecular engineering strategies toward a cellulosic E. coli. Lactic acid production from cellulose will be used to demonstrate the successful strategy and illustrate the application of the engineered cells for production of useful products from renewable cellulose material.