Biotransformation of tributyltin chloride to less toxic dibutyltin dichloride and monobutyltin trichloride by Klebsiella pneumoniae strain SD9

Abstract

A tributyltin chloride (TBTCl) resistant bacterial strain was isolated from the Zuari estuary, in Goa, India, and identified as Klebsiella pneumoniae based on biochemical characteristics and 16S rRNA sequence analysis, and designated as strain SD9. It could utilize TBTCl as a sole carbon source in mineral salt medium and tolerated up to 2.5 mM TBTCl with maximum growth at 2 mM. Nuclear magnetic resonance spectroscopic analysis of column purified TBTCl degradation products clearly demonstrated the presence of dibutyltin dichloride (DBTCl2) and monobutyltin trichloride (MBTCl3). Mass spectrometry further confirmed degradation of toxic TBTCl into its less toxic derivatives, viz., DBTCl2 and MBTCl3. This strain also showed enhanced siderophore production in the presence of TBTCl, which was demonstrated by chrome azurol S agar assay as an increase in diameter of the orange halo around the bacterial colony in the presence of 2 mM TBTCl; this seems to be a mechanism to counteract TBTCl toxicity. Furthermore, scanning electron microscopy revealed significant morphological alterations as shrinkage in cell size along with roughness of cell surface when bacterial cells were exposed to 2 mM TBTCl. These interesting characteristics of this estuarine bacterium make it a potential tool for bioremediation of TBTCl contaminated sites since it possesses biotransformation capability to convert TBTCl into DBTCl2 and MBTCl3.