Horiyama Tsukasa, Nishino Kunihiko
Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan.
Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan; Laboratory of Microbiology and Infectious Diseases, Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan.
PLoS One. 2014 Sep 26;9(9):e108642. doi: 10.1371/journal.pone.0108642. eCollection 2014.
Escherichia coli produces the iron-chelating compound enterobactin to enable growth under iron-limiting conditions. After biosynthesis, enterobactin is released from the cell. However, the enterobactin export system is not fully understood. Previous studies have suggested that the outer membrane channel TolC is involved in enterobactin export. There are several multidrug efflux transporters belonging to resistance-nodulation-cell division (RND) family that require interaction with TolC to function. Therefore, several RND transporters may be responsible for enterobactin export. In this study, we investigated whether RND transporters are involved in enterobactin export using deletion mutants of multidrug transporters in E. coli. Single deletions of acrB, acrD, mdtABC, acrEF, or mdtEF did not affect the ability of E. coli to excrete enterobactin, whereas deletion of tolC did affect enterobactin export. We found that multiple deletion of acrB, acrD, and mdtABC resulted in a significant decrease in enterobactin export and that plasmids carrying the acrAB, acrD, or mdtABC genes restored the decrease in enterobactin export exhibited by the ΔacrB acrD mdtABC mutant. These results indicate that AcrB, AcrD, and MdtABC are required for the secretion of enterobactin.
大肠杆菌产生铁螯合化合物肠杆菌素，以便在铁限制条件下生长。生物合成后，肠杆菌素从细胞中释放出来。然而，肠杆菌素的输出系统尚未完全了解。先前的研究表明，外膜通道TolC参与肠杆菌素的输出。有几种属于耐药-固氮-细胞分裂（RND）家族的多药外排转运蛋白需要与TolC相互作用才能发挥功能。因此，几种RND转运蛋白可能负责肠杆菌素的输出。在本研究中，我们使用大肠杆菌中多药转运蛋白的缺失突变体来研究RND转运蛋白是否参与肠杆菌素的输出。单独缺失acrB、acrD、mdtABC、acrEF或mdtEF并不影响大肠杆菌排泄肠杆菌素的能力，而缺失tolC则确实影响肠杆菌素的输出。我们发现，acrB、acrD和mdtABC的多重缺失导致肠杆菌素输出显著减少，并且携带acrAB、acrD或mdtABC基因的质粒恢复了ΔacrB acrD mdtABC突变体所表现出的肠杆菌素输出减少。这些结果表明，AcrB、AcrD和MdtABC是肠杆菌素分泌所必需的。
