Method for determining microbial activity (hydrolysis of fluorescein diacetate (FDA), 490 nm)

Abstract

Abstract Fluorescein diacetate (FDA) is used to determine microbial activity. The determination of this activity can be carried out within the frame of various study objects using soil, litter, peat, etc. This method is based on a hydrolysis reaction of converting fluorescein diacetate (FDA) to fluorescein. The concentration is usually determined using a spectrophotometer in the UV range. This article discusses the possible concentration of fluorescence in the visible spectrum (490 nm). The activity of microorganisms was determined in the Chernozem typical arable horizon. The work used two methods for determining the concentration of fluorescence by optical density. The first option is to use a calibration concentration (the dependence of optical density on the concentration of fluorescein). In this case two options were used: with heating (60 °C) and without it (25 °C). The second option is to use the Bouguer-Lambert-Beer equation and the extinction coefficient. The results were used for calculating the Michaelis-Menten constants (Km) and the maximum reaction rate (Vm). While determining the microbial activity with FDA, the concentration of fluorescein can be determined in the visible range. The more preferable way of determining the concentration of fluorescein is by using the extinction coefficient of fluorescein, rather than by plotting a calibration graph based on matrix solutions.