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Applied and Environmental Microbiology, May 2006, p. 3119-3129, Vol. 72, No. 5
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.5.3119-3129.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Pyridine-2,6-Bis(Thiocarboxylic Acid) Produced by Pseudomonas stutzeri KC Reduces and Precipitates Selenium and Tellurium Oxyanions

Anna M. Zawadzka, Ronald L. Crawford, and Andrzej J. Paszczynski*

Environmental Biotechnology Institute, University of Idaho, Moscow, Idaho 83844-1052

Received 22 November 2005/ Accepted 16 February 2006

The siderophore of Pseudomonas stutzeri KC, pyridine-2,6-bis(thiocarboxylic acid) (pdtc), is shown to detoxify selenium and tellurium oxyanions in bacterial cultures. A mechanism for pdtc's detoxification of tellurite and selenite is proposed. The mechanism is based upon determination using mass spectrometry and energy-dispersive X-ray spectrometry of the chemical structures of compounds formed during initial reactions of tellurite and selenite with pdtc. Selenite and tellurite are reduced by pdtc or its hydrolysis product H2S, forming zero-valent pdtc selenides and pdtc tellurides that precipitate from solution. These insoluble compounds then hydrolyze, releasing nanometer-sized particles of elemental selenium or tellurium. Electron microscopy studies showed both extracellular precipitation and internal deposition of these metalloids by bacterial cells. The precipitates formed with synthetic pdtc were similar to those formed in pdtc-producing cultures of P. stutzeri KC. Culture filtrates of P. stutzeri KC containing pdtc were also active in removing selenite and precipitating elemental selenium and tellurium. The pdtc-producing wild-type strain KC conferred higher tolerance against selenite and tellurite toxicity than a pdtc-negative mutant strain, CTN1. These observations support the hypothesis that pdtc not only functions as a siderophore but also is involved in an initial line of defense against toxicity from various metals and metalloids.

* Corresponding author. Mailing address: Environmental Biotechnology Institute, University of Idaho, Food Research Center 103, P.O. Box 441052, Moscow, ID 83844-1052. Phone: (208) 885-6318. Fax: (208) 885-5741. E-mail: andrzej{at}uidaho.edu.

Applied and Environmental Microbiology, May 2006, p. 3119-3129, Vol. 72, No. 5
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.5.3119-3129.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.





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