GSE114148
Sphingobium chlorophenolicum Confronts the Stresses Associated with Pentachlorophenol and Four Toxic Downstream Metabolites to Utilize a Suboptimal Nutrient Source [Tn-Seq]
Pentachlorophenol (PCP) is a highly toxic pesticide that was first introduced in the 1930s. The a-proteobacterium Sphingobium chlorophenolicum, which was isolated from PCP-contaminated sediment, has assembled a metabolic pathway capable of mineralizing PCP. Interestingly, this pathway produces four toxic intermediates, which include a chlorinated benzoquinone that is a potent alkylating agent and three chlorinated hydroquinones that produce reactive oxygen species and benzoquinones upon reaction with O2. We sought to identify how the cell tolerates the onslaught of toxic effects associated with these intermediates. RNA-Seq and Tn-Seq were used to probe the response of S. chlorophenolicum to PCP as well as the stresses associated with its exposure and degradation. The results demonstrate that PCP exposure causes dissipation of the proton-motive force and perturbation of the cell envelope, and the downstream intermediates cause oxidative stress. However, the transcriptional response to PCP degradation far exceeds what is actually needed and, for many genes, is actually counter-productive. Prevention of PCP degradation by deletion of the transcriptional regulator, pcpR, increases growth rate in rich medium. These data suggest that, although PCP degradation allows access to a novel nutrient, the benefit of degrading it depends upon the availability of other resources. When resources are abundant, the detrimental effects of the toxic intermediates may outweigh the benefit of the carbon and energy that can be obtained by degrading PCP. However, when resources are scarce, degradation of PCP may provide access to a novel source of carbon and energy as well as detoxification of this anthropogenic pollutant. Overall design: Transposon mutant libraries were created in wild type S. chlorophenolicum and in S. chlorophenolicum ?pcpB (a mutant which cannot degrade PCP). Libraries were grown in the absence or presence of 200 µM pentachlorophenol for 22-24 generations. Libraries were then subjected to Tn-Seq analysis for fitness determinations of individual mutants. This analysis allowed us to determine genes important for fitness during exposure to PCP as well as specifically those important during degradation of PCP.