Soil Oxidoreductases and FDA Hydrolysis

The oxidoreductases comprise the largest enzyme group and consist of enzymes that catalyze reactions in which one substrate is oxidized (the donor) while another is reduced (the acceptor). This chapter proposes the use of an assay for fluorescein diacetate (FDA) hydrolysis as an alternative indicator of overall enzymatic activity in soil. FDA hydrolysis is mediated by a number of different enzymes, including lipases, proteases, and esterases, and appears to be ubiquitous among fungi and bacteria that are the primary decomposers in the soil. Organisms that degrade plant and other organic residues have been identified as major contributors to soil enzyme activity. Therefore, since FDA hydrolysis is a wide-ranging assay of soil hydrolase activities, it should represent microbial activity and have an important role in soil microbial ecology. FDA hydrolysis is based on the following enzyme-mediated reaction, The product, fluorescein, is extracted and measured by spectrophotometry.