Influences of chemical speciation and solid phase partitioning on microbial toxicity : single organism to in situ community response
Moberly, James Gill
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The waters and sediments of Lake Coeur d'Alene (LCDA) in northern Idaho have been contaminated by heavy metals because of decades of mining operations. Metal speciation is critical in assessing toxicity because it may vary considerably with pH and is dependent on other aqueous constituents. There has been little research on integrated investigations of the effects of heavy metal speciation on indigenous microbes from LCDA, especially large scale community analysis. The focus of this research in the LCDA system was to determine the effect of heavy metal speciation on toxicity, first in a defined single organism system, followed by in situ studies. Combined results of thermodynamic modeling, statistical analysis, and batch culture studies using Arthrobacter sp. JM018 suggest that the toxic species is not solely limited to the free ion, but also includes ZnHPO 4 0(aq). Cellular uptake of ZnHPO 4 0(aq) through the inorganic phosphate transporter (pit family), which requires a neutral metal phosphate complex for phosphate transport, may explain the observed toxicity. These findings show the important role of "minor" Zn species in organism toxicity and have wider implications since the pit inorganic phosphate transport system is widely distributed in bacteria, archaea, and eukaryotes. Using a multivariate statistical approach, correlations between the microbial community (via 16S rDNA microarray) in sediment cores and operationally defined heavy metal phases (via continuous sequential extractions) were explored. Candidate phyla NC10, OP8 and LD1PA were only present in metal contaminated cores and diversity doubled among Natronoanaerobium in metal contaminated cores which may suggest some increased fitness of these phyla in contaminated sediments. Correlations show decreases in diversity from presumed sulfate reducing lineages within most taxa from Desulfovibrionales and Bdellovibrionales and from metal reducing bacterial lineages Shewanellaceae, Geobacteraceae, and Rhodocyclaceae with increases in the ratio of more bioavailable Pb exchangeable/carbonate to less bioavailable Pb oxyhydroxide. This is the first time these techniques have been used in combination to describe a contaminated system.