Long Term Effects of Heavy Metal Contamination on Bacterial Communities in the Upper Clark Fork River Canyon

Abstract

Microorganisms and their activities drive most ecosystems and therefore must be assessed in order to study ecosystem stability. Heavy metal contamination is known to have adverse effects on soil bacteria. In this study, bacterial populations from polluted (PV and PB) and non-polluted (NV) soils were compared in order to better understand soil resiliency, ecosystem stability, and the long-term effects of heavy metals have on bacteria. Biological parameters of soil quality including diversity, structure, activity, and heavy metal tolerance were compared and assessed. The numbers of Zn and Cu tolerant bacteria were determined by spread plating diluted soil samples onto agar plates containing 0.5,2, and 10 mM concentrations of the metals. Arginine and iodonitrotetrazolium assays were used to measure the extent of ammonification and dehydrogenase activity in the soil. And, 16S rDNA cloning and sequencing was used to identify 60 individual microorganisms from both the NV and PV soils. Neighbor-joining phylogenetic trees, constructed with the 16S rDNA clones, were then used to analyze differences in bacterial diversity and community structure. I hypothesized that the population in the NV soil would: 1) have higher activity levels, 2) be more diverse, 3) contain fewer metal tolerant microorganisms, and 4) show a different community structure than the bacterial populations isolated from the polluted soils. All hypotheses were found to be correct except for the hypothesis addressing the diversity of the two soils (NV and PV). It was found that both soils were very diverse in bacterial species and that 60 clones from each soil was not a big enough sample size to address the differences in diversity between the two bacterial populations isolated from the two soils.