Pseudomonas putida mutants in the exbBexbDtonB gene cluster are hypersensitive to environmental and chemical stressors

The genes in the exbBexbDtonB cluster of Pseudomonas putida DOT-T1E are co-transcribed. We have generated non-polar mutants in each of the genes by inserting an aphA3 cassette encoding kanamycin resistance. All three mutants show similar phenotypes: the mutants are unable to grow on minimal medium under iron deficiency conditions. Furthermore, regardless of iron conditions, all mutants are hypersensitive to antibiotics, p-hydroxybenzoate and toluene, chemicals that are extruded from the cell by efflux pumps. These findings are discussed in terms of the involvement of the TonB system in the energization of outer membrane functions necessary for the import or export of different compounds in P. putida.