Assessment of fluorescein diacetate hydrolysis as a measure of total esterase activity in natural stream sediment biofilms

I applied the fluorescein diacetate (FDA) hydrolysis technique as a rapid and sensitive estimator of total esterase activity in stream sediment biofilms. I investigated the effects of temperature, pH and incubation time and optimized the assay for low blanks and high fluorescein extraction. The FDA procedure was precise (c.v. = 4.15%) and could detect 10 nM fluorescein. Spatial patterns of esterase activity within stream sediment biofilms correlated with electron transport system activity, bacterial thymidine incorporation, glucosidase activity and chlorophyll a. As such, I suggest the modified and optimized technique as applicable to the investigation of total stream bioflim esterase activity.