The potential of soil protein-based methods to indicate metal contamination

Abstract

Soil metal contamination is an international problem and there is a recognised need for methods to detect the effects of such pollution. To this end, we investigated the use of soil protein extraction, quantification and expression as indicators of cadmium contamination of soil. A variety of methods to extract total soil protein were examined and the effects of cadmium and lime treatment on total soil protein, protein expression and microbial biomass were determined. A simple snap freeze protein extraction technique (using liquid nitrogen) was found to extract the most protein from soil samples compared to a bead beating method used commonly for DNA extraction from soil. Using the snap freeze method, cadmium (Cd) contamination was observed to significantly decrease total soil protein levels compared to an uncontaminated control soil (16 μg g −1 cf. 24 μg g −1) whilst liming significantly increased total soil protein in the control and contaminated treatments (35 and 22 μg g −1). These results were related to similar, but less pronounced, changes in microbial biomass in Cd contaminated and limed control soils. Limed Cd contaminated soils had similar amounts of total soil protein to unlimed control soils. The protein profiles (SDS-PAGE) of extracted soil protein from control and cadmium contaminated soils concentrated by both acetone precipitation and heating showed no obvious changes in protein expression between treatments. However, large amounts of presumably low molecular weight proteins (<21 kDa) were observed at the bottom of the protein profiles from the contaminated soils.