Sucrose-to-Bioproducts: Engineering a Sucrose-Based E. Coli Platform for Industrial Bioproduction

Sucrose from sugarcane is a preferable carbon source for industrial bioprocesses due to low cost and superior environmental performance compared to glucose. E. coli is an important industrial production organism; however, most industrial E. coli strains cannot utilize sucrose. We have identified a sucrose-utilizing E. coli strain which shows promise as an industrial production strain. E. coli W grows very quickly, can be grown to high cell density, and has good tolerance for bioprocess stresses. Using this strain, we have developed a number of tools which form a platform for sucrose-based E. coli bioprocesses: (a) The genome of E. coli W was sequenced and annotated, and a genome scale metabolic model was developed to facilitate strain improvement. Refinements in our E. coli metabolic reconstruction allow it to more accurately define E. coli metabolism relative to previous models. (b) Transferring sucrose utilisation capacity to non-utilising strains has met with limited success in the past; we developed an approach to successfully transfer the E. coli W csc sucrose utilisation genes to non-sucrose utilising strains, allowing the engineered strains to use sucrose efficiently and, in most cases, to grow on sucrose as fast as the wild type strains could grow on glucose (c) Wild-type W cannot grow on low sucrose concentrations; this is undesirable for industrial fed-batch bioprocesses where sugar concentrations remain low between feeding pulses. Knock-out of the csc repressor resulted in a strain which could grow efficiently on low sucrose and which had improved production of the model biochemical polyhydroxybutyrate (PHB).

Using the transfer approach we developed, strains which are already heavily engineered for production of specific biochemicals can be altered to use sucrose instead of glucose. We are now starting to use the improved strains and other tools for production of isoprenoid compounds (isoprene and isoprenoid aviation fuels) from sucrose. The tools that we have created will allow further development of E. coli W and other strains as industrial organisms for sucrose-based E. coli bioprocesses. This will encourage use of sucrose as a carbon source and assist in transition of our petrochemical-based economy to a bio-based economy.