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Appl. Environ. Microbiol., Mar 1997, 951-955, Vol 63, No. 3
RF Bonsall, DM Weller and LS Thomashow
The broad-spectrum antibiotic 2,4-diacetylphloroglucinol (Phl) is a major
determinant in the biological control of a wide range of plant diseases by
fluorescent Pseudomonas spp. A protocol was developed to readily isolate
and quantify Phl from broth and agar cultures and from the rhizosphere
environment of plants. Extraction with ethyl acetate at an acidic pH was
suitable for both in vitro and in situ sources of Phl. For soil samples,
the addition of an initial extraction step with 80% acetone at an acidic pH
was highly effective in eliminating polar organic soil components, such as
humic and fulvic acids, which can interfere with Phl detection by
high-performance liquid chromotography. The efficiency of Phl recovery from
soil by a single extraction averaged 54.6%, and a second extraction added
another 6.1%. These yields were substantially greater than those achieved
by several standard protocols commonly used to extract polar phenolic
compounds from soil. For the first time Phl was isolated from the
rhizosphere environment in raw soil. Following application of Pseudomonas
fluorescens Q2-87 and the Phl-overproducing strain Q2-87(pPHL5122) to the
seeds of wheat, 2.1 and 2.4 (mu)g of Phl/g of root plus rhizosphere soil,
respectively, were isolated from wheat grown in a Ritzville silt loam; 0.47
and 1.3 (mu)g of Phl/g of root plus rhizosphere soil, respectively, were
isolated from wheat grown in a Shano silt loam. However, when the amount of
Phl was calculated on the basis of cell density, Q2-87(pPHL5122) produced
seven and six times more antibiotic than Q2-87 in Ritzville silt loam, and
Shano silt loam, respectively.
Copyright © 1997, American Society for Microbiology
Quantification of 2,4-Diacetylphloroglucinol Produced by Fluorescent Pseudomonas spp. In Vitro and in the Rhizosphere of Wheat
Department of Plant Pathology, Washington State University, and Root Disease and Biological Control Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Pullman, Washington 99164-6430
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