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Identification and characterization of Pseudomonas membrane transporters necessary for utilization of the siderophore pyridine-2,6-bis(thiocarboxylic acid) (PDTC)

Department of Microbiology and Molecular Genetics, University of Vermont, 95 Carrigan Drive, Burlington, VT 05405, USA

Correspondence
Thomas A. Lewis
talewis{at}uvm.edu

The compound pyridine-2,6-bis(thiocarboxylic acid) (PDTC) is known to be produced and excreted by three strains of Pseudomonas. Its reactivity includes the complete dechlorination of the environmental contaminant carbon tetrachloride. PDTC functions as a siderophore; however, roles as a ferric reductant and antimicrobial agent have also been proposed. PDTC function and regulation were further explored by characterizing the phenotypes of mutants in predicted membrane transporter genes. The functions of a predicted outer-membrane transporter (PdtK) and a predicted inner-membrane permease (PdtE) were examined in Pseudomonas putida DSM 3601. Uptake of iron from ⁵⁵Fe(III):PDTC, and bioutilization of PDTC in a chelated medium, were dependent upon PdtK and PdtE. Another strain of P. putida (KT2440), which lacks pdt orthologues, showed growth inhibition by PDTC that could be relieved by introducing a plasmid containing pdtKCPE. Transcriptional activation in response to exogenously added PDTC (25 µM) was unaltered by the pdtK or pdtE mutations; each mutant showed activation of a pdt transcriptional reporter, indistinguishable from an isogenic PDTC utilization-proficient strain. The data demonstrate that PdtK and PdtE constitute a bipartite outer-membrane/inner-membrane transport system for iron acquisition from Fe(III):PDTC. Disruptions in this portion of the P. putida DSM 3601 pdt gene cluster do not abolish PDTC-dependent transcriptional signalling.

This article has been cited by other articles:

				S. E. Morales and T. A. Lewis Transcriptional Regulation of the pdt Gene Cluster of Pseudomonas stutzeri KC Involves an AraC/XylS Family Transcriptional Activator (PdtC) and the Cognate Siderophore Pyridine-2,6-Bis(Thiocarboxylic Acid) Appl. Envir. Microbiol., November 1, 2006; 72(11): 6994 - 7002. [Abstract] [Full Text] [PDF]