Characterization of the structural and functional diversity of indigenous soil microbial communities in smelter-impacted and nonimpacted soils.

A century of mining and smelting activity at the Anaconda Smelter site in Anaconda, Montana, USA, has contaminated the surrounding soils and groundwater with metals. Soil microbial communities from six smelter-impacted sites and a nonimpacted site were compared to determine the long-term effects of a gradient of metal concentrations on microbial activity, biomass, functional diversity (Biolog microtiter plates), and structural diversity (denaturant gradient gel electrophoresis of 16S ribosomal DNA). Microbial activity and biomass were decreased in the smelter-impacted soils. Likewise, the functional and structural diversity of the microbial communities native to the smelter-impacted soils were shifted, relative to the microbial community, from the nonimpacted site. These shifts were significantly correlated with soil metal concentration and several soil physicochemical properties (pH, organic matter, NO(3), NH(4), etc.), which provides evidence of the importance of many environmental variables on microbial community dynamics in soils. Preliminary evidence of functional redundancy was observed within microbial communities native to the smelter-impacted sites, based on overlapping carbon substrate utilization patterns. However, due to culture-based selection bias, redundancy pertains only to a subset of the community and may not be ecologically relevant. Nevertheless, the effects of metal contamination on microbial communities in the present study are pronounced and results provide preliminary insight into the complex relationship between soil microbial community structure and function in anthropogenically disturbed soils.