Membrane damage during production of biorenewable fuels and chemicals and compensatory membrane engineering strategies

The production of fuels and chemicals from biomass in a manner that is economically competitive with petroleum-based processes is often hindered by microbial inhibition by the product and/or impurities in the biomass-derived sugar stream. In many of these cases, this inhibition of the microbial biocatalyst involves membrane damage. This talk will describe the various metrics for characterizing this problem, give examples of membrane damage during utilization of biomass-derived sugars and production of carboxylic acids and styrene, and describe two distinct methods for strengthening the Escherichia coli membrane. The first engineering strategy is enabling homeoviscous adaptation in E. coli, resulting in a significant increase in membrane fluidity and improved tolerance to a variety of inhibitors. The second membrane engineering strategy involves altering the distribution of the native phospholipid head groups. One such engineering strategy was associated with increased tolerance of carboxylic acids, various biomass-associated inhibitors (such as furfural), aromatic monomers, low pH and low temperature. This increased tolerance of carboxylic acids was accompanied by a substantial increase in membrane integrity and a 40% increase in fatty acid titers. Finally, by implementing Orgel’s Second Rule that “evolution is cleverer than you are”, we can find inspiration for other membrane engineering strategies. Two such membrane engineering strategies inspired by reverse engineering of evolved E. coli strains will be discussed.