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Applied and Environmental Microbiology, April 2003, p. 2023-2031, Vol. 69, No. 4
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.4.2023-2031.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Isolation and Antifungal and Antioomycete Activities of Aerugine Produced by Pseudomonas fluorescens Strain MM-B16

Laboratory of Molecular Plant Pathology, College of Life and Environmental Sciences, Korea University, Seoul 136-701,¹ Department of Chemistry, Kongju National University, Kongju 314-701, Korea²

Received 7 August 2002/ Accepted 2 January 2003

The bacterial strain MM-B16, which showed strong antifungal and antioomycete activity against some plant pathogens, was isolated from a mountain forest soil in Korea. Based on the physiological and biochemical characteristics and 16S ribosomal DNA sequence analysis, the bacterial strain MM-B16 was identical to Pseudomonas fluorescens. An antibiotic active against Colletotrichum orbiculare and Phytophthora capsici in vitro and in vivo was isolated from the culture filtrates of P. fluorescens strain MM-B16 using various chromatographic procedures. The molecular formula of the antibiotic was deduced to be C₁₀H₁₁NO₂S (M⁺, m/z 209.0513) by analysis of electron impact mass spectral data. Based on the nuclear magnetic resonance and infrared spectral data, the antibiotic was confirmed to have the structure of a thiazoline derivative, aerugine [4-hydroxymethyl-2-(2-hydroxyphenyl)-2-thiazoline]. C. orbiculare, P. capsici, and Pythium ultimum were most sensitive to aerugine (MICs for these organisms were approximately 10 µg ml^-1). However, no antimicrobial activity was found against yeasts and bacteria even at concentrations of more than 100 µg ml^-1. Treatment with aerugine exhibited a significantly high protective activity against development of phytophthora disease on pepper and anthracnose on cucumber. However, the control efficacy of aerugine against the diseases was in general somewhat less than that of the commercial fungicides metalaxyl and chlorothalonil. This is the first study to isolate aerugine from P. fluorescens and demonstrate its in vitro and in vivo antifungal and antioomycete activities against C. orbiculare and P. capsici.