Abstract
Engineering of efflux pumps is a promising way to improve host’s tolerance to biofuels such as medium-chain alcohols (CmOHs); however, this strategy is restricted by poor understanding of the efflux pumps engaged in extrusion of solvents. In this study, several Escherichia coli mutants of multidrug transporters were evaluated for isoprenol tolerance. Susceptible phenotypes were observed in the mutants with individual deletion of six transporters, AcrD, EmrAB, MacAB, MdtBC, MdtJI and YdiM, whereas inactivation of AcrAB transporter resulted in an improved tolerance to isoprenol and other CmOHs. AcrAB is the major transporter forming tripartite transperiplasmic complex with outer membrane channel TolC for direct extrusion of toxic molecules in E. coli. The AcrAB inactivation enables to enhance TolC availability for the multidrug transporters associated with extrusion of CmOHs and increase the tolerance to CmOHs including isoprenol. It is assumed that outer membrane channel TolC plays an important role in extrusion of isoprenol and other CmOHs.
Highlights
Engineering of efflux pumps is a promising way to improve host’s tolerance to biofuels such as medium-chain alcohols (CmOHs); this strategy is restricted by poor understanding of the efflux pumps engaged in extrusion of solvents
There are at least 37 putative multidrug transporters (MDTs) found in Escherichia coli, belonging to five different families: major facilitator (MF) family, small multidrug resistance (SMR) family, resistance nodulation cell division (RND) family, ATP-binding cassette (ABC) family and multidrug and toxic compound extrusion (MATE) family[16]
Several multidrug transporter (MDT) mutants are susceptible to isoprenol
Summary
Engineering of efflux pumps is a promising way to improve host’s tolerance to biofuels such as medium-chain alcohols (CmOHs); this strategy is restricted by poor understanding of the efflux pumps engaged in extrusion of solvents. To probe native isoprenol transporters, it was assumed that any deletion of MDT gene associated with isoprenol extrusion would result in a reduced tolerance phenotype in comparison with the wild type E. coli (Fig. 1A,B). To explore the possible transporters for isoprenol extrusion, cell growth was evaluated after 12 h exposure to 0.5% (v/v) of isoprenol in a total of 44 MDT null mutants (Fig. 1C and Supplementary Table S3).
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