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Applied and Environmental Microbiology, November 2003, p. 6464-6474, Vol. 69, No. 11
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.11.6464-6474.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Low-Temperature Isolation of Disease-Suppressive Bacteria and Characterization of a Distinctive Group of Pseudomonads

P. Maria Johansson1* and Sandra A. I. Wright2*

Plant Pathology and Biocontrol Unit, Sveriges Lantbruksuniversitet, SE-750 07 Uppsala,1 Department of Cellular and Molecular Biology, Göteborg University, SE-405 30 Göteborg, Sweden2

Received 21 July 2003/ Accepted 6 August 2003

The influence of environmental factors during isolation on the composition of potential biocontrol isolates is largely unknown. Bacterial isolates that efficiently suppressed wheat seedling blight caused by Fusarium culmorum were found by isolating psychrotrophic, root-associated bacteria and by screening them in a bioassay that mimicked field conditions. The impact of individual isolation factors on the disease-suppressive index (DSI) of almost 600 isolates was analyzed. The bacteria originated from 135 samples from 62 sites in Sweden and Switzerland. The isolation factors that increased the probability of finding isolates with high DSIs were sampling from arable land, Swiss origin of samples, and origination of isolates from plants belonging to the family Brassicaceae. The colony morphology of the isolates was characterized and compared to DSIs, which led to identification of a uniform morphological group containing 57 highly disease-suppressive isolates. Isolates in this group were identified as Pseudomonas sp.; they were fluorescent on King's medium B and had characteristic crystalline structures in their colonies. These isolates were morphologically similar to seven strains that had previously been selected for suppression of barley net blotch caused by Drechslera teres. Members of this morphological group grow at 1.5°C and produce an antifungal polyketide (2,3-deepoxy-2,3-didehydrorhizoxin [DDR]). They have similar two-dimensional polyacrylamide gel electrophoresis protein profiles, phenotypic characteristics, and in vitro inhibition spectra of pathogens. In summary, in this paper we describe some isolation factors that are important for obtaining disease-suppressive bacteria in our system, and we describe a novel group of biocontrol pseudomonads.

* Corresponding author. Mailing address for P. Maria Johansson: Plant Pathology and Biocontrol Unit, SLU, Box 7035, 75007 Uppsala, Sweden. Phone: 46-18-303158. Fax: 46-18-671690. E-mail: Maria.Johansson{at}vpat.slu.se. Mailing address for Sandra A. I. Wright: Department of Cellular and Molecular Biology, Göteborg University, Box 462, 405 30 Göteborg, Sweden. Phone: 46-18-671605. Fax: 46-18-671690. E-mail: Sandra.Wright{at}molbio.gu.se.

Applied and Environmental Microbiology, November 2003, p. 6464-6474, Vol. 69, No. 11
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.11.6464-6474.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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