Tin-Carbon Cleavage of Organotin Compounds by Pyoverdine from Pseudomonas chlororaphis

Abstract

The triphenyltin (TPT)-degrading bacterium Pseudomonas chlororaphis CNR15 produces extracellular yellow substances to degrade TPT. Three substances (F-I, F-IIa, and F-IIb) were purified, and their structural and catalytic properties were characterized. The primary structure of F-I was established using two-dimensional nuclear magnetic resonance techniques; the structure was identical to that of suc-pyoverdine from P. chlororaphis ATCC 9446, which is a peptide siderophore produced by fluorescent pseudomonads. Spectral and isoelectric-focusing analyses revealed that F-IIa and F-IIb were also pyoverdines, differing only in the acyl substituent attached to the chromophore part of F-I. Furthermore, we found that the fluorescent pseudomonads producing pyoverdines structurally different from F-I showed TPT degradation activity in the solid extracts of their culture supernatants. F-I and F-IIa degraded TPT to monophenyltin via diphenyltin (DPT) and degraded DPT and dibutyltin to monophenyltin and monobutyltin, respectively. The total amount of organotin metabolites produced by TPT degradation was nearly equivalent to that of the F-I added to the reaction mixture, whereas DPT degradation was not influenced by monophenyltin production. The TPT degradation activity of F-I was remarkably inhibited by the addition of metal ions chelated with pyoverdine. On the other hand, the activity of DPT was increased 13-and 8-fold by the addition of Cu 2؉ and Sn 4؉ , respectively. These results suggest that metal-chelating ligands common to pyoverdines may play important roles in the Sn-C cleavage of organotin compounds in both the metal-free and metal-complexed states.Organotin compounds, in particular tributyltin (TBT) and triphenyltin (TPT), have been extensively used as an active component in antifouling paints and agrochemicals over the last 40 years. These compounds have been introduced into aquatic systems via leaching from the antifouling paints and runoff from agricultural fields (9, 10, 18, 32), causing harmful effects on a variety of nontarget organisms, such as plankton (8,20), gastropods (3, 16), and fish (11), even at low nanomolar aqueous concentrations. In recent years, the application of TBT and TPT in antifouling agents has been restricted in many countries, but these compounds have continued to be detected in the biota, water, and sediments because of their persistence. Thus, organotin contamination has been considered to be one of the most important ecotoxicological problems.The slow disappearance of organotin from the environment is caused by various processes: photolysis by sunlight, chemical cleavage by strong acid or electrophilic agents, and biological degradation (12, 34). These processes involve a sequential removal of organic groups, which generally results in a reduction of toxicity. It remains unclear whether the biological degradation of organotin compounds is due to an enzymatic reaction, because no enzyme catalyzing the Sn-C cleavage reaction is known yet. The debutylation of TBT by microorganisms using ...

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Biochemistry of TBT-Degrading Marine Pseudomonads Isolated from Indian Coastal Waters

“…In this study, P. putida NIOT20 produced pyoverdines which was confirmed by thin layer chromatography (picture not shown). Inoue et al 2003 reported TPT degradation by a pyoverdine-secreting pseudomonad P. chlororaphis CNR15 isolated in Japan. They also confirmed both TBT and TPT degradation activities in culture supernatants of certain bacteria in which no pyoverdine was detected by IEF analysis; suggesting that the degradation reaction of organotin compounds is likely to occur by chelation of tin by certain types of siderophores.…”

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