Involvement of MexS and MexEF-OprN in Resistance to Toxic Ion Chelators in <i>Pseudomonas putida</i> KT2440

• Main Authors: Tania Henriquez, Tom Baldow, Yat Kei Lo, Dina Weydert, Andreas Brachmann, Heinrich Jung
• Format: Article
• Language: English
• Published: MDPI AG 2020-11-01
• Series: Microorganisms
• Subjects: <i>Pseudomonas</i>; second site revertant; RND transporter; bipyridyls
• Online Access: https://www.mdpi.com/2076-2607/8/11/1782

Bacteria must be able to cope with harsh environments to survive. In Gram-negative bacteria like <i>Pseudomonas</i> species, resistance-nodulation-division (RND) transporters contribute to this task by pumping toxic compounds out of cells. Previously, we found that the RND system TtgABC of <i>Pseudomonas putida</i> KT2440 confers resistance to toxic metal chelators of the bipyridyl group. Here, we report that the incubation of a <i>ttgB</i> mutant in medium containing 2,2’-bipyridyl generated revertant strains able to grow in the presence of this compound. This trait was related to alterations in the pp_2827 locus (homolog of <i>mexS</i> in <i>Pseudomonas aeruginosa</i>). The deletion and complementation of pp_2827 confirmed the importance of the locus for the revertant phenotype. Furthermore, alteration in the pp_2827 locus stimulated expression of the <i>mexEF-oprN</i> operon encoding an RND efflux pump. Deletion and complementation of <i>mexF</i> confirmed that the latter system can compensate the growth defect of the <i>ttgB</i> mutant in the presence of 2,2’-bipyridyl. To our knowledge, this is the first report on a role of pp_2827 (<i>mexS</i>) in the regulation of <i>mexEF-oprN</i> in <i>P. putida</i> KT2440. The results expand the information about the significance of MexEF-OprN in the stress response of <i>P. putida</i> KT2440 and the mechanisms for coping with bipyridyl toxicity.