Metallothionein assisted periplasmic lead sequestration as lead sulfite by Providencia vermicola strain SJ2A.

Lead resistant Providencia vermicola strain SJ2A was isolated from the waste of a battery manufacturing industry which could tolerate upto 3.0mM lead nitrate in the minimal medium. Interestingly, this isolate showed presence of a plasmid borne metallothionein gene, bmtA that matched significantly (96%) with that of Pseudomonas aeruginosa. Scanning electron micrographs of bacterial cells exposed to lead revealed a unique alteration in the cell morphology from rods to long inter-connected filaments. On the other hand, electron dispersive X-ray spectroscopy (EDX) clearly indicated no significant lead adsorption therefore, we speculated intracellular sequestration in this bacterial strain. Transmission electron micrographs of the bacterial cells exposed to lead evidently demonstrated periplasmic sequestration of lead which was also supported by Fourier transformed infrared spectroscopic (FTIR) analysis. The bacterium internalised 155.12mg Pb2+/g biomass as determined by atomic absorption spectroscopy. Subsequently, the accumulated lead was identified as lead sulfite by X-ray diffraction studies. Therefore P. vermicola strain SJ2A has potential to bioremediate lead contaminated environmental sites.