Threonine dehydratase enhances bacterial cadmium resistance via driving cysteine desulfuration and biomineralization of cadmium sulfide nanocrystals.

Biomineralization is often used by microorganisms to sequester heavy metal ions and provides a potential means for remediating increasing levels of heavy metal pollution. Bacteria have been shown to utilize cysteine for the biomineralization of metal sulfide. Indeed, in the present study, the supplement of L-cysteine was found to significantly improve both cadmium resistance and removal abilities of a deep-sea bacterium Pseudomonas stutzeri 273 through cadmium sulfide (CdS) nanoparticle biomineralization. With a proteomic approach, threonine dehydratase of P. stutzeri 273 (psTD) was proposed to be a key factor enhancing bacterial cadmium resistance through catalyzing L-cysteine desulfuration, H2S generation and CdS nanoparticle biomineralization. Consistently, deletion of the gene encoding psTD in P. stutzeri 273 resulted in the decline of H2S generation, decrease of cadmium resistance, and reduction of cadmium removal ability, confirming the unique function of psTD directing the formation of CdS nanoparticles. Correspondingly, the single-enzyme biomineralization of CdS nanoparticle driven by psTD was further developed, and psTD was shown to act as a capping reagent for the mineralization reaction, which controlling the size and structure of nanocrystals. Our results provide important clues for the construction of engineered bacteria for cadmium bioremediation and widen the synthesis methods of nanomaterials.