Abstract
ABSTRACT: Among soil microorganisms, the genus Cupriavidus has garnered particular scientific, economic and ecological interest because of its ability to fix nitrogen and tolerate high concentrations of metals. The aim of this study was to analyze four strains of Cupriavidus necator for their ability to tolerate and bioaccumulate cadmium and zinc. The tolerance of these strains to these metals was assessed in liquid culture medium containing different concentrations of Zn + Cd and in soil solutions and soils contaminated with multiple elements including Zn, Cd, Cu and Pb. The four strains showed high tolerance to Zn and Cd, both in culture medium and when inoculated into contaminated soil solutions or multi-element contaminated soil. The UFLA02-71 strain displayed the highest ability to bioaccumulate these metals. It was able to accumulate 93.76 µmol g cell−1 of Zn and 16.03 µmol g cell−1 of Cd when cultured in liquid medium with a total heavy metal concentration of 9,140 µmol L−1 (9,000 Zn + 140 Cd) and was able to accumulate 16.98 µmol g cell−1 of Cd in the soil solution. An increase in the pH of the culture medium resulting from the growth of the C. necator strains reduced the Zn2+ and Cd2+ ions in the medium and increased the concentrations of the ZnHPO4 and CdHPO4 species in solution. Thus, we concluded that they show great potential for use in the bioremediation of HM-contaminated areas.
Highlights
Several microorganisms are capable of colonizing heavy metals (HM)-contaminated environments due to a wide range of mechanisms and interactions that allow them to adapt to these environments (Sharaff and Archana, 2015)
The main tolerance mechanisms of microorganisms are related to the active transporting of metals across the membrane and out of the cell, resistance plasmids with genes encoding to heavy metal tolerance, adsorption of metals by the cell wall, and biotransformation of the metals directly by specific enzymes or indirectly by cellular metabolites (Gadd, 2004)
The strains grown at the highest concentration of heavy metals had a prolonged period of growth but grew at lower rates than the cultures grown in low concentrations of Zn + Cd
Summary
Several microorganisms are capable of colonizing HM-contaminated environments due to a wide range of mechanisms and interactions that allow them to adapt to these environments (Sharaff and Archana, 2015). Other species of the Cupriavidus genus that were isolated from tailing pond sediments at a zinc factory have garnered interest for their potential use in bioremediation, including Cupriavidus metallidurans, this specie does not fix nitrogen. These species are well known for being highly tolerant of Zn, Cd, Co, Ni, Cu, Cr, Hg and Pb (Taghavi et al, 1997; Goris et al, 2001; Mergeay et al, 2003) and for their ability to biodegrade recalcitrant xenobiotic compounds (Louie et al, 2002; Trefault et al, 2004). There are no studies examining the tolerance of Cupriavidus necator under multi-element HM-contamination conditions either in culture medium or using contaminated soils
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