Abstract
Bacteria must be able to cope with harsh environments to survive. In Gram-negative bacteria like Pseudomonas 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 Pseudomonas putida KT2440 confers resistance to toxic metal chelators of the bipyridyl group. Here, we report that the incubation of a ttgB 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 mexS in Pseudomonas aeruginosa). 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 mexEF-oprN operon encoding an RND efflux pump. Deletion and complementation of mexF confirmed that the latter system can compensate the growth defect of the ttgB mutant in the presence of 2,2’-bipyridyl. To our knowledge, this is the first report on a role of pp_2827 (mexS) in the regulation of mexEF-oprN in P. putida KT2440. The results expand the information about the significance of MexEF-OprN in the stress response of P. putida KT2440 and the mechanisms for coping with bipyridyl toxicity.
Highlights
Pseudomonas species are Gram-negative rod-shaped bacteria that exhibit a highly versatile range of activities, including acting as plant protectants or animal pathogens [1,2]
We described that in P. putida KT2440 the RND system TtgABC is needed in order to cope with the toxicity of the metal chelating compounds 2,2’-bipyridyl (Bip) and caerulomycin (a 2,2’-bipyridyl-derivaive produced by bacteria and normally found in the environment [14]) [15]
In a colony morphology assay on King’s Broth (KB) agar plates supplemented with 1 mM Bip, P. putida KT2440 formed a large colony, while the ∆ttgB mutant yielded very small colonies in the inoculated area within 24 h (Figure 1A)
Summary
Pseudomonas species are Gram-negative rod-shaped bacteria that exhibit a highly versatile range of activities, including acting as plant protectants (such as Pseudomonas putida) or animal pathogens (such as Pseudomonas aeruginosa) [1,2]. The mutation leading to this phenotype can be located in mexT (coding for a regulator of mexEF-oprN and oprD) [9], mexS (regulator of mexT) [9], mexEF-oprN, oprD, mvaT [10], ampR [11] (the latter two genes code for transcriptional regulators), or in other unknown regions of the genome [12,13] While most of this information on MexEF-OprN and its regulatory network was derived from clinical isolates of P. aeruginosa, little is known about the role and regulation of the RND system in other species, including P. putida
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