The Effects of Zinc Contamination on Soil Bacterial Communities

Abstract

Relatively little is known about the effects of soil metal contamination on bacteria in laboratory environments. Extensive field studies have been done on the long-term effects of metal contamination on soil communities while relatively few studies have been performed in controlled environments. Zinc contamination is known to have an adverse effect on soil microorganisms that are important to ecosystem stability. The ability of microorganisms to adapt after an initial contamination is important in natural environments that may become contaminated. In this study the proportion of Zn tolerant bacteria and the activity of soil microorganisms were tested 2 days, 32 days, and 62 days after the initial contamination of soil with Zn levels of 12.5 mM and increasing to 25 and 50 mM. Numbers of Zn tolerant bacteria were determined using 15% tryptone soy agar plates containing 0, 2, and 10 mM Zinc. Microbial activity was measured using two assays: an arginine assay for ammonification activity and an iodonitrotetrazolium assay for dehydrogenase activity. Concentration of soil-zinc had a significant effect on ammonification and dehydrogenase activity in soil during the study period. Soils contaminated with zinc had a significant increase in the proportion of the total community tolerant to Zn. Populations tolerant to 2 and 10 mM zinc were significant at the P<0.00033 and P<3.9E-09 respectively.