Accumulation and Partitioning of Heavy Metals by Bacterial Cells and Associated Colloidal Minerals, with Alteration, Neoformation, and Selective Adsorption of Minerals by Bacteria, in Metal-Polluted Lake Sediment

Abstract

Energy dispersive X-ray microanalysis and transmission electron microscopy were used to investigate heavy metal accumulation and partitioning by a statistically meaningful assortment of bacteria and colloidal minerals in metal-polluted lake sediment. Visually selected external and internal parts of bacterial cells were analysed individually. Variations in element distribution and relationships provided clues to small-scale biogeochemical processes and their implications for microbial ecology. Most bacteria had mineral coatings of varying composition and texture formed by adsorption of detrital clay and precipitation of authigenic oxides and clay attributable to Fe and Al complexing by cell walls and fibrils. Fe oxide precipitated abiotically and indiscriminately on bacteria and minerals, but Mn oxide was purely biogenic, precipitating only on certain bacteria. Cell walls also complexed Cu; formation of mineral coatings interfered with Cu binding, but the coatings themselves scavenged Cu. Cu and Zn were bound preferentially by oxides, but Ni was bound mainly by clay. Many bacteria accumulated metals preferentially on cell exteriors or in cytoplasmic inclusions, implying different mechanisms of bioaccumulation and detoxification, whose original purpose may have been to concentrate nutrient trace metals from dilute solution and regulate their proportions. Bacteria commonly employed both mechanisms, suggesting adaptation to different metal species. Preferential intake and exclusion of metals also occurred, and exterior-interior partition coefficients of metals in cells correlated with specific metal properties, revealing clues to the processes involved. In addition, bacteria were important agents of diagenesis. Besides precipitating oxides, they degraded adsorbed clay, synthesised intracellular and extracellular clay, and adsorbed clay minerals selectively.

Keywords:

• heavy metals
• bacteria
• colloidal minerals
• sediment
• lake
• energy dispersive X-ray microanalysis

Acknowledgments

The field work was carried out by M.R. Mawhinney, F. Rosa, R.D. Coker, and K. Zhou, and we thank F. Rosa for contributing the data for the lake water. The bulk chemical analyses and microbiological assays were performed by N. Nguyen, and the X-ray diffraction analyses were done by W. M. Last (Department of Geological Sciences, University of Manitoba). The electron microscopy and microanalyses, including preliminary work done by D.T. Flannigan, were performed with facilities of the Department of Biology and Faculty of Health Sciences, McMaster University. The research was supported by funds from Environment Canada (Government of Canada), including a grant from the Commercial Chemicals Evaluation Branch and a grant provided through the Metals in the Environment (MITE) programme.