Role of the DmpR-Mediated Regulatory Circuit in Bacterial Biodegradation Properties in Methylphenol-Amended Soils

Abstract

Pathway substrates and some structural analogues directly activate the regulatory protein DmpR to promote transcription of the dmp operon genes encoding the (methyl)phenol degradative pathway of Pseudomonas sp. strain CF600. While a wide range of phenols can activate DmpR, the location and nature of substituents on the basic phenolic ring can limit the level of activation and thus utilization of some compounds as assessed by growth on plates. Here we address the role of the aromatic effector response of DmpR in determining degradative properties in two soil matrices that provide different nutritional conditions. Using the wild-type system and an isogenic counterpart containing a DmpR mutant with enhanced ability to respond to para-substituted phenols, we demonstrate (i) that the enhanced in vitro biodegradative capacity of the regulator mutant strain is manifested in the two different soil types and (ii) that exposure of the wild-type strain to 4-methylphenol-contaminated soil led to rapid selection of a subpopulation exhibiting enhanced capacities to degrade the compound. Genetic and functional analyses of 10 of these derivatives demonstrated that all harbored a single mutation in the sensory domain of DmpR that mediated the phenotype in each case. These findings establish a dominating role for the aromatic effector response of DmpR in determining degradation properties. Moreover, the results indicate that the ability to rapidly adapt regulator properties to different profiles of polluting compounds may underlie the evolutionary success of DmpR-like regulators in controlling aromatic catabolic pathways.

Degradation of mixtures of phenolic compounds by Arthrobacter chlorophenolicus A6

“…Alternatively micro-scale niches in the soil environment may be present where the halogenated phenols were reduced sufficiently to enable localized onset of phenol degradation. The soil conditions could possibly also promote rapid adaptation of A. chlorophenolicus to the substrates present as reported previously for another phenol-degrading strain (Sarand et al 2001).…”

Expression of the Nitroarene Dioxygenase Genes inComamonassp. Strain JS765 andAcidovoraxsp. Strain JS42 Is Induced by Multiple Aromatic Compounds

“…Also, the regulators of TOL meta-cleavage pathway genes, XylS and XylS1, differ in only five amino acids but have different effector profiles and display different sigma factor dependence (37). Finally, the ability of bacterial strains to grow with multiple hydroxylated aromatic substrates has been linked to enhanced effector responses, such as those caused by single-amino-acid changes in DmpR, a regulator of phenol degradation genes (40). Therefore, it seems reasonable that the few differences between NtdR and NagR could drastically alter the effector profile as well as the observed basal level of expression.…”

Engineering input/output nodes in prokaryotic regulatory circuits

“…A plasmid carrying DmpR was introduced into the selection Po-km strain (Po is the promoter activated by DmpR). Further analysis demonstrated that these strains had point mutations within the A domain of DmpR, which produced an enhanced response to 4-methylphenol (Sarand et al, 2001). This produced one mutant bearing a point mutation in the A domain of the protein, which displayed not only a novel response to 4-ethylphenol but also showed an increased reaction to 4-methyphenol and 3,4-dimethyphenol.…”