Palladium recovery as nanoparticles by an anaerobic bacterial community

BACKGROUND: Bio-recovery of metals from dilute industrial waste using bacteria is a promising alternative to primary raw material resources. Therefore, the search for and identification of palladium resistant bacteria with the ability to remove that metal from solutions is very important. The main goal of this study was to find a palladium(II) resistant bacterial community able to bio-recover this metal from solution. RESULTS: A palladium(II) resistant bacterial community able to precipitate that metal from the growth medium was obtained from a sludge sample from a municipal waste water treatment plant. This community was able to remove 60% of palladium(II) from an aqueous solution containing 18 mg L^-1 of Pd(II) and 43% in the presence of 26 mg L^-1 Pd(II) plus sulphate. TEM-EDS analysis showed the presence of nanosized palladium deposits in the surface of cells. Phylogenetic analysis of the 16S rRNA gene showed that this community was mainly composed of bacteria closely related to several Clostridium species. However, bacteria affiliated to genera Bacteroides and Citrobacter were also present in the community. CONCLUSION: The current study for the first time reports the bio-recovery of Pd(II) as nanoparticles by a bacterial consortium, and is a relevant demonstration of the biotechnological potentialities of this community.