Project description: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.
Project description: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.
Project description:Nickel is an essential component of many eukaryotic and prokaryotic metallo-enzymes. Due to its employment in many industrial applications, wastewaters from industrial plants often contain millimolar concentrations of Ni2+ that are toxic and life-threatening for many organism. Several lines of preliminary evidence suggest that members of the genus Sphingobium are able to grow in the presence of high concentrations of metal ions. We have isolated a novel Sphingobium strain (sp. ba1) able to grow in the presence of high concentrations (up to 20 mM) of NiCl2. Sequencing of its genome allowed the identification of several genes coding for proteins potentially involved in efflux-mediated resistance mechanisms. Here we use the RNA-seq approach to analyze the response of the Sphingobium sp. ba1 strain to high concentrations (10 mM) of Ni ions. Transcriptomic data show the differential expression of about one-hundred and twenty genes, most of which are up-regulated and encode proteins such as membrane proteins and components of metal efflux systems, enzymes involved in oxidative stress responses (catalases, peroxidases) and signal transduction systems.
