Saturday, 15 July 2006

Isolation and Characterization of Antifungal Substances from Culture Broth of Burkholderia sp.

Mao Sopheareth, Jin Rong De, Park Mi Jung, Kim Yong Woong, and Kim Kil Yong. Division of Applied BioScience and Biotechnology, College of Agriculture and Life Science, Chonnam National Univ, 300, Yong Bong Dong, Buk Ku, Gwangju, South Korea

A new antagonistic Burkholderia strain, designated as MP-1 and producing antifungal activities against various plant pathogenic fungi, was isolated from the rhizoshere in Naju area. Cultural characteristic studies strongly suggested that this strain belongs to the genus Burkholderia. The nucleotide sequence of the 16S rRNA gene (1491 pb) of strain MP-1 exhibited close similarity (99-100%) with other Burkholderia 16S rRNA genes. Bacterial culture broth was extracted with ethyl acetate (EtOAc) and partitioned with a NaHCO3 buffer solution. The EtOAc-soluble acidic fraction was then sequentially purified by silica gel, Sephadex LH-20, ODS column chromatography, and high performance liquid chromatography. Various separation and purification steps led to isolation of four pure active molecules. The chemical structure of these four compounds, named as phenylacetic acid (PA), hydrocinnamic acid (HA), 4-hydroxyphenylacetic acid (4HPA), and 4-hydroxyphenylacetate methyl ester (4HPME), was established on the basis of GC-EI-MS and trimethylsilation GC-EI-MS data. Each isolated substance inhibited fungal growth on potato dextrose agar supplemented with 100 ppm. When each compound was treated to Phytophthora capsici, the walls of hyphae were deformed and destroyed as illustrated by light microscopy. We suggest that Burkholderia sp. MP-1 could be good candidate to be used in the biocontrol of plant pathogens. The concentration and nature of ecosystem can exploit these compounds as a plant growth regulator or fungicide, and further studies are needed to evaluate this possibility.

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