ARS | Publication request: OPTIMIZATION OF THE FLUORESCEIN DIACETATE HYDROLYSIS (FDA) ASSAY IN SOIL

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: August 30, 1996
Publication Date: N/A

Technical Abstract: The hydrolysis of fluorescein diacetate (3¿, 6¿-diacetylfluorescein [FDA]) has been suggested as a general measurement of microbial activity in soils. This is because lipase, protease and esterase are the enzymes involved in the hydrolysis. During hydrolysis, fluorescein is released and can then be measured by spectrophotometry. The objective of this study was to optimize the FDA hydrolysis assay in soils. The method developed involves extraction and determination of the fluorescein released when 2.5 g of soil are incubated with 50 ml of 60 mM buffered, (pH 7.0) sodium phosphate solution at 35 degree C for 24 hour. Results showed that FDA hydrolysis was optimum at buffer pH 7.0 and the soil enzymes were denatured at temperatures above 50 degree C. The initial rates of flourescein release obeyed zero-order kinetics. Three soils were used in the study: a silty clay loam, a silt loam and a sand. The FDA hydrolysis in three soils studied ranged from 1800 to 9000 mg fluorescein released per g soil per 24 hour incubation, with more hydrolysis occurring in the silty clay loam.