Recently, antagonistic bacteria are attracting global attention as a source of biocontrol agents for agricultural land. Commonly, the bacteria used for this purpose are screened and isolated under high nutrient conditions and/or under special culture conditions for antibiotics production to obtain as much candidates as possible. However, normally, the organic nutrients levels in soils are much lower than those in the isolation medium, and consequently, the isolated bacteria are often unable to grow enough to show antagonistic effect in soils. Therefore, we focused on oligotrophic bacteria as a new isolation source of biocontrol agents. Here we report isolation and identification of two candidate bacteria together with their antagonistic activities toward several plant pathogens.  Microbes were isolated from soils, surfaces of plant leaves, insides of seed kernels and, puddles around our university using a minimum mineral medium (MM) supplemented with small carbon source (<100ppm), and incubated at 30�C, 200 rpm for 1 week. As a result, 22 microbes showed high growth capacity in the MM and two of these named strain KS and DE showed strong growth inhibitory activities against plant fungal pathogens including Rhizoctonia solani, Colletotrichum orbiculare, and Monilinia fructigena. KS also exhibited antibacterial activity against Bacillus subtilis. The 16S rDNA analysis of these strains suggested that KS and DE were closely related to Burkholderia contaminans and Pseudomonas protegens, respectively. The structure elucidation using MS and NMR spectroscopies revealed that pyrrolnitrin was major active antifungal constituent in both strains and 2,4-diacetylphloroglucinol was the antibacterial compound in KS. In this session, we would like to discuss the potential application of these strains as biocontrol agents.

Potential application of oligotrophic bacteria as biocontrol agents

248th National Meeting (2014)

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