Sinorhizobium, a potential organism for bioremediation of nickel

Heavy metals represent a great environmental concern, because of their widespread use, distribution, and toxicity to human beings. The growing environmental awareness necessitates the development of effective and inexpensive methods for metal removal. In the present study an attempt was made to examine the nickel tolerating abilities of Rhizobium sp. nodulating Sesbania sesban. The biosorption capability of the isolate was studied using synthetic nickel solution. Out of the 22 Rhizobium and Sinorhizobium isolates, Sinorhizobium sp. BEL5B (JX444691.1) tolerated the highest Ni concentration (3mM) and was used for further studies. The scanning electron microscopy micrographs revealed morphological changes and secretions of extra polymeric substances. The biosorption of nickel was highly influenced by parameters like pH, biomass dosage and metal concentration. The biosorption data followed the Langmuir and Freundlich isotherm models. The maximum biosorption capacity for nickel by BEL5B was found to be 25.13mg/g. The FTIR spectroscopy studies showed the involvement of cell surface ligands in metal biosorption. Further, alkali pretreatement with NaOH was found to increase the biosorption capacity for nickel in BEL5B biomass. Thus, on the basis of all these parameters studied a better insight was obtained into the tolerance mechanisms as well as the bioremediating capabilities of this well know biofertilizer.