Root colonization by a plant-beneficial rhizobacterium, Pseudomonas chlororaphis O6, induces disease resistance in tobacco against leaf pathogens Erwinia carotovora subsp. carotovora SCC1, causing soft-rot, and Pseudomonas syringae pv. tabaci, causing wildfire. In order to identify the bacterial determinants involved in induced systemic resistance against plant diseases, extracellular components produced by the bacterium were fractionated and purified. Factors in the culture filtrate inducing systemic resistance were retained in the aqueous fraction rather than being partitioned into ethyl acetate. Fractionation on high-performance liquid chromatography followed by nuclear magnetic resonance mass spectrometry analysis identified the active compound as 2R, 3R-butanediol. 2R, 3R butanediol induced systemic resistance in tobacco to E. carotovora subsp. carotovora SCC1, but not to P. syringae pv. tabaci. Treatment of tobacco with the volatile 2R, 3R-butanediol enhanced aerial growth, a phenomenon also seen in plants colonized by P. chlororaphis O6. The isomeric form of the butanediol was important because 2S, 3S-butandiol did not affect the plant. The global sensor kinase, GacS, of P. chlororaphis O6 was a key regulator for induced systemic resistance against E. carotovora through regulation of 2R, 3R-butanediol production. This is the first report of the production of these assumed fermentation products by a pseudomonad and the role of the sensor kinase GacS in production of 2R, 3R-butanediol.

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We compared the immunomodulating effects of Phellinus linteus (PL), germinated brown rice (BR) and P. linteus grown on germinated brown rice (PB) on IgE production in murine mesenteric lymph node (MLN) lymphocytes. All extracts decreased IgE concentrations by 43--65% compared to control mice in both serum and MLN lymphocytes. In addition, PL and PB increased the proportion of CD4(+) T cells by 9% and 12% in MLN lymphocytes. IFN-gamma concentration, Th1 cytokine, was significantly increased by 44--67%, whereas IL-4 and IL-10 concentrations, Th2 cytokine, significantly decreased by 30--60% in the three treated groups compared to control group. These results suggest that PB suppresses IgE production through the modulation of Th1/Th2 balance to down-regulate Th2 response in MLN lymphocytes, even though a synergistic effect of PB was not found.

This study was undertaken to describe purification, identification, and characteristics of protocatechuic acid (PCA) isolated for the first time from Paenibacillus elgii HOA73 against Botrytis cinerea (the cause of gray mold disease on strawberry fruit). PCA was purified by different chromatographic techniques and identified as PCA (3,4-dihydroxybenzoic acid) by nuclear magnetic resonance and liquid chromatography-mass spectrometry analyses. PCA displayed potent antifungal activity against B. cinerea and Rhizoctonia solani. However, the antifungal activities were not sufficient to inhibit mycelial growth of Phytophthora capsici and Fusarium oxysporum. The minimum inhibitory concentration of PCA to inhibit any visible mycelial growth of both B. cinerea and R. solani was 64 µg ml(-1) . Most B. cinerea conidia displayed altered shape and absence of germination, or were degraded after treatment with 50 and 100 µg ml(-1) PCA, respectively. Moreover, gray mold formation on strawberry fruit was almost or completely inhibited by these PCA concentrations 7 days following infection with B. cinerea conidia, respectively. PCA may be a promising alternative to chemical fungicides as a potential biofungicide to prevent growth of B. cinerea in strawberry fruit disease management.

In this study, evidences for antagonism were established by production of antifungal metabolites from Streptomyces griseus H7602, which were active to inhibit mycelial growth of Phytophthora capsici in the in vitro assays. Mycelial growth and zoosporangia formation of P. capsici was strongly inhibited in the medium containing the cell free culture filtrate of S. griseus H7602. Antifungal metabolites from the cell free culture filtrate of S. griseus H7602 showed substantial antagonistic effects on P. capsici. In addition, a purified antifungal compound was separated from the antifungal metabolites of S. griseus H7602 and identified to be 1H-pyrrole-2-carboxylic acid (PCA) by spectra analyses. PCA showed strong antifungal activity and was evaluated for the first time for its antagonism against P. capsici under in vitro conditions. Minimum inhibitory concentration (MIC) value of PCA was low (4 µg ml(-1)), and the mycelial growth of P. capsici was almost inhibited at concentration of 64 µg ml(-1). This study suggests that the PCA may be useful as biofungicides against P. capsici, and the prominent antagonism of antifungal metabolites from S. griseus H7602 highlights it as a candidate for biocontrol of P. capsici.