Quantifying Soil Microbial Respiration with a Fluorometric Dye.

Microbial respiration is integral to a variety of soil characteristics including carbon cycling and soil fertility. Given the important services soils provide to humans, it is beneficial to have methods to accurately measure the microbial activity present in soil. Applications for such methods range from agriculture to bioremediation. There are methods that currently exist for quantifying soil microbial respiration, but they have several cons such as inaccuracies, complicated laboratory techniques, and lengthy procedures. This project’s purpose was to the attempt to develop a new method of soil microbial respiration quantification using a fluorometric dye. The dye used is a chemical called resazurin (RAZ) that was originally designed as a tracer for surface water applications. This dye reacts biochemically with enzymes present in the mitochondria of heterotrophic microorganisms during respiration, becoming irreversibly reduced into another chemical called resorufin (RRU). RRU is fluorescent, as well as extremely chemically stable. It was hypothesized that the rate of RAZ reduction to RRU could be an indicator of soil microbial respiration rate. This project focused on observing the rate of RRU production over time in soil samples inoculated with RAZ. RRU concentration was estimated using a standard curve of RRU fluorescence. RRU production rates were compared across different soil types. RRU production rates were also correlated to other measures of soil microbial activity. One final aim of this project was to test sterilized soil samples to verify a lack of RRU production, or observe and identify a level of purely physiochemical RRU production. The development of a new, accurate, cheap, and simple method in measuring soil microbial activity would be extremely beneficial for many, especially those in agriculture and other soil involved industries. The use of resazurin as an effective measure of soil microbial activity could prove to be this “new” method. It is recommended further research is pursued in examining resazurin as a tool for soil metabolome quantification.