Isolation and In vitro and In vivo antifungal activity of phenylacetic acid produced by Micromonospora aurantiaca strain JK-1

Abstract

The actinomycete strain JK-1 that showed strong inhibitory activity against some plant pathogenic fungi and oomycetes was isolated from Jung-bal Mountain in Ko-yang, Korea. The strain JK-1 produced spores singly borne on sporophores and the spores were spherical and 0.9-1.2 μm in diameter. The cell wall of the strain JK-1 contained meso-diaminopimelic acid. The actinomycete strain JK-1 was identified as the genus Micromonospora based on the morphological, physiological, biochemical and chemotaxonomic characteristics. From the 16S rDNA analysis, the strain JK-1 was assigned to M. aurantiaca. The antibiotic MA-1 was purified from the culture broth of M. aurantiaca JK-1 using various purification procedures, such as Diaion HP20 chromatography, C18 flash column chromatography, silica gel flash column chromatography and Sephadex LH-20 column chromatography. 1H-, 13C-NMR and EI mass spectral analysis of the antibiotic MA-1 revealed that the antibiotic MA-1 is identical to phenylacetic acid. Phenylacetic acid showed in vitro inhibitory effects against fungal and oomycete pathogens Alternaria mali, Botrytis cinerea, Magnaporthe grisea, Phytophthora capsici and yeast Saccharomyces cerevisiae at < 100 μg ml-1. In addition, phenylacetic acid completely inhibited the growth of Sclerotinia sclerotiorum, Bacillus subtilis, Candida albicans, Xanthomonas campestris pv. vesicatoria at < 500 μg ml-1. Phenylacetic acid strongly inhibited conidial germination and hyphal growth of M. grisea and C. orbiculare. Phenylacetic acid showed significantly high levels of inhibitory effect against rice blast and cucumber anthracnose diseases at 250 μg ml-1. The control efficacies of phenylacetic acid against the two diseases were similar to those of commercial compounds tricyclazole, iprobenfos and chlorothalonil in the greenhouse. © The Korean Society of Plant Pathology.