Toward efficient microaerobic processes using engineered Escherichia coli W3110 strains

Abstract

Operational and economic constraints in large‐scale bioreactors often result in local or global microaerobic conditions, which lead to less efficient bioprocesses. Escherichia coli adapts to microaerobicity by activating fermentation pathways that accumulate acidic by‐products, in detriment of growth rate (μ) and biomass yield on glucose (YX/S). In this study, the metabolism of E. coli was modified to better cope with microaerobicity. For that purpose, genes coding for global regulators like carbon source responsive B protein and aerobic respiratory control A protein, or for fermentative pathways were inactivated. The performance of a wild‐type (W3110) and engineered E. coli strains was evaluated in batch cultures at constant low dissolved oxygen tension (3% air sat.). By combining the partial elimination of fermentation pathways and the expression of the Vitreoscilla hemoglobin (VHb), a 32% decrease on carbon waste as by‐products, 24 % increase on YX/S and 13% increase of μ were obtained. Flux balance analysis of the best strain estimated major differences in the fluxes through the pentose phosphate pathway and tricarboxylic acid cycle as consequence of VHb presence. Overall, our results show that E. coli can be genetically modified to overcome some of the disadvantages of microaerobic growth, which is potentially useful for better bioreactor scale‐up and operation.