The role of the siderophore pyridine-2,6-bis (thiocarboxylic acid) (PDTC) in zinc utilization by Pseudomonas putida DSM 3601

Abstract

Previous work had suggested that in addition to serving the function of a siderophore, pyridine-2,6-bis(thiocarboxylic acid) (PDTC) may also provide producing organisms with the ability to assimilate other divalent transition metals. This was tested further by examining regulation of siderophore production, expression of pdt genes, and growth in response to added zinc. In media containing 10-50 microM ZnCl2, the production of PDTC was found to be differentially repressed, as compared with the production of pyoverdine. The expression of PdtK, the outer membrane receptor involved in PDTC transport, was also reduced in response to added zinc whereas other iron-regulated outer membrane proteins were not. Expression of a chromosomal pdtI: xylE fusion was repressed to a similar extent in response to zinc or iron. Mutants that cannot produce PDTC did not show a growth enhancement with micromolar concentrations of zinc as seen in the wild type strain. The phenotype of the mutant strains was suppressed by the addition of PDTC. The outer membrane receptor and inner membrane permease components of PDTC utilization were necessary for relief of chelator (1,10-phenanthroline)-induced growth inhibition by Zn:PDTC. Iron uptake from 55Fe:PDTC was not affected by a 32-fold molar excess of Zn:PDTC. The data indicate that zinc present as Zn:PDTC can be utilized by strains possessing PDTC utilization functions but that transport is much less efficient than for Fe:PDTC.

Beyond iron: non-classical biological functions of bacterial siderophores

“…68 Subsequent studies revealed that the zinc-pdtc complex is recognized and transported by the outer membrane receptor and inner membrane permease of the pdtc utilization machinery; however, transport of zinc-pdtc is much less efficient than transport of the iron-pdtc complex. 69 …”

Chalkophores

“…Stabilization of harder transition metals like nickel and iron requires bischelate formation, and despite demonstrated iron binding (199), pdtc’s role in iron uptake may rely partly on its ability to reduce iron (198, 200). Nevertheless, uptake of Fe(III)-pdtc and of Zn-pdtc (201, 202) has been the major biological focus, and whether pdtc is a true chalkophore is unclear. Cu-pdtc appears to have other unusual properties, including the ability to dechlorinate the carcinogen carbon tetrachloride (203).…”

Metallophores and Trace Metal Biogeochemistry

“…Siderophore-mediated uptake is not known; aqueous Mn(III) is stabilized and strongly bound by known Fe(III)-siderophores (Duckworth and Sposito 2005b;Farkas and Szabo 2012;Faulkner et al 1994;Harrington et al 2012a, b;Parker et al 2004) B B is an essential element to plants and may be beneficial to bacteria and animals (Adriano 2001) B is bound by several iron siderophores and may be associated with signaling in the ocean (Harris et al 2007) W Some prokaryotic redox enzymes, most notably in thermophilic bacteria (Kletzin and Adams 1996) No metallophores have been identified; however, W binds to azotochelin and protochelin, but is not taken up by A. vinelandii (Wichard et al 2008) Zn Many diverse enzymes (Morel et al 2006) No metallophores have been identified; however, there is a possible role of pyridine-2,6-bisthiocarboxylic acid (PDTC) in uptake (Leach et al 2007) by…”