Soil zymography – A novel in situ method for mapping distribution of enzyme activity in soil

Recently, there has been growing interest in the spatial distribution of microbial activity in soil; however, methods for analysis of spatial distribution of microbial activity and for localization of hotspots of enzyme activity in soil are limited. Here were present an in situ zymography technique for localization and quantification of enzyme activities in soil by means of thin gels with embedded substrates. After incubation, the substrate remaining in the gel is colored and quantified using calibration curves and digital image analysis. So far, zymography has mostly been used to localize enzymatic activity in electrophoresis gels and in tissue sections. In this study we developed a zymography technique for analysis of the two-dimensional distribution of enzyme activities in soil. The technique was applied to map and quantify protease and amylase activity in the rhizosphere of lupine (Lupinus polyphyllus) grown in rhizoboxes. Highest activities, of up to 46 ng mm−2 of the soil surface h−1 for the protease and of up to 0.90 μg mm−2 h−1 for the amylase were found in close association with roots. Since zymography is an in situ method that does not require destruction of soil structure, it likely pictures enzyme activities more realistically than standard enzyme assays. In conclusion, soil in situ zymography offers a promising tool for mapping distributions of enzyme activities in soils in a work- and cost-efficient way.