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use of FDA to detect soil microbes

Bruce A. Caldwell caldwelb at fsl.orst.edu
Tue Jul 24 16:52:49 EST 2001

HI --
FDA is a non-specific esterase substrate and not a direct indicator of
life.  Many cell-free soil enzymes (e.g., phosphatases, lipases) can
react with this substrate.

A better approach would be to use one of several chromogenic terminal
electron acceptors (TTC, INT) which actually response to microbial
metabolism.  There are many papers on this (dehydrogenase) assay.
Basically, you incubate the soil with substrate and then extract the
reduced "formazan" with methanol. Microbial respiratiopn turns the
colorless INT or TTC to red-purple "formazan".

Good luck,
Bruce Caldwell
Dept of Forest Science
321 Richardson Hall
Oregon State University
Corvallis  OR  97331-5752

martin weiss wrote:

> We have developed an activity for visitors to detect life in soil
> using fluorescein diacetate (in DMSO). However, the reaction proceeds
> very slowly reaching a peak after a day or so.
> Does anyone have any suggestions to speed up the reaction?. We've
> tried heat (55 C) and SDS (2% final) to no avail.
> Cheers,
> Martin
> --
> Martin Weiss, Ph.D.
> Director of Science
> New York Hall of Science
> 47-01 111 th Street
> Corona, New York 11368
> phone: 718 699 0005 x 356
> facsimile:718 699 1341
> mweiss at nyhallsci.org
> http://www.nyhallsci.org
> ---

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