Effects of Varying Concentrations of Zinc on Bacterial Tolerance, Diversity, and Community Structure in Artificially Amended Soils

Abstract

Controlled experiments in laboratory settings examining the effect of zinc pollution on bacterial communities in soil often neglect metal exposure over a period of time. Increasing levels of soil-zinc have been shown to increase the Zn tolerance of bacterial communities in soil and decrease diversity and change community structure of bacterial populations. Since soils are a critical component of terrestrial systems, the soil must be able to recover from a pollution event in order to maintain the quality of natural and agricultural systems. This study analyzed bacterial tolerance and diversity in soils containing 0,12.5,25, and 50 mM Zn after a year of incubation in a laboratory setting. Approximately 50 16S rDNA clones from each soil (0,25, and 50 mM Zn) were sequenced and analyzed by neighbor joining. There was an increase in tolerance with increasing Zn concentration in soil, and there was also an increase in tolerance from a year previous. Both the arginine and dehydrogenase assays showed a decrease in activity with increasing Zn concentration. The diversity of the communities changed little with 40 unique species in the control and 37 and 36 unique species in the 25 and 50 mM Zn amended soils, respectively. The structure of the communities also exhibited a small change as both the number of species in each taxon changed, and the taxa that were present changed with Zn concentration.