(191ao) Membrane Engineering in Escherichia coli to Enhance Production of Bio-Fuels and Chemicals

The production of advanced biofuels and chemicals has advanced substantially in the last decade. Methods for improving the performance of engineered microbes includes a wide range of strategies, from the overexpression of existing genes to the replacement of entire pathways. Experimental results and in silico models have shown that tolerance is often related to production. In other words, the economic viability of bio-based production systems is highly dependent on the performance of the engineered microbial cell factory. Low production titers of bio-products compromise their ability to economically compete with petroleum-based processes. We aim to increase microbial production of biofuels and biochemicals, such as ethanol, butanol, phenol and styrene, by increasing microbial robustness to these inhibitors. Particularly, the cell membrane is frequently damaged by accumulation of these chemicals, decreasing the production capacity of the microbial cell factory. Engineering of the membrane has been demonstrated both to increase tolerance towards these inhibitors and to enable increased production of biofuels and chemicals.

Previously, our lab demonstrated that membrane engineering could improve the production of both octanoic acid and styrene (Tan et al., 2016). Specifically, Escherichia coli was engineered to isomerize some of the membrane-associated cis-unsaturated fatty acids to the trans form via expression of the Cti enzyme from Pseudomonas aeruginosa. This engineering strategy enabled a tighter packing of phospholipids in the membrane, resulting in increased rigidity. Currently, the ability of this engineering strategy to improve tolerance and production of other important membrane-damaging compounds is being further explored. We are also tuning the saturated and unsaturated (S/U) fatty acid ratio, as well as other membrane properties. This strategy offers additional insight into compatibility of chemicals produced and the microbial cell factory. These strategies enable higher tolerance towards certain chemicals of interest, advanced biofuels and inhibitory compounds associated with lignocellulose treatment. An increase in tolerance will allow us to not only to enhance production, but also to decrease the associated unit operations for processing feedstock for advanced biofuels production. Thus, current economic limitations for biofuel production at large scale could be reduced.