Trade-Offs in Improving Biofuel Tolerance Using Combinations of Efflux Pumps

Microbes
can be engineered to produce next-generation biofuels;
however, the accumulation of toxic biofuels can limit yields. Previous
studies have shown that efflux pumps can increase biofuel tolerance
and improve production. Here, we asked whether expressing multiple
pumps in combination could further increase biofuel tolerance. Pump
overexpression inhibits cell growth, suggesting a trade-off between
biofuel and pump toxicity. With multiple pumps, it is unclear how
the fitness landscape is impacted. To address this, we measured tolerance
of Escherichia coli to the biojet fuel precursor
α-pinene in one-pump and two-pump strains. To support our experiments,
we developed a mathematical model describing toxicity due to biofuel
and overexpression of pumps. We found that data from one-pump strains
can accurately predict the performance of two-pump strains. This result
suggests that it may be possible to dramatically reduce the number
of experiments required for characterizing the effects of combined
biofuel tolerance mechanisms.