Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2006
Publication Date: 3/2/2007
Citation: Haiming, L., Yanjing, H., Haixia, J., Huasong, P., Xianqing, H., Xuehong, Z., Thomashow, L.S., Yuquan, X. 2007. Characterization of a phenazine-producing strain Pseudomonas chlororaphis GP72 with broad-spectrum antifungal activity from green pepper rhizosphere. Current Microbiology.
Interpretive Summary: Root diseases caused by soilborne pathogens are major yield-limiting factors in the production of food, fiber and ornamental crops. Trends in agriculture toward greater sustainability and less dependence on synthetic fungicides have created a need for more ecologically sound methods of disease control. Biological control exploits the natural antagonistic activity of certain root-colonizing bacteria against plant pathogens and is considered the best alternative for the control of certain soilborne root diseases of wheat. This study focused on Pseudomonas chlororaphis GP72, a new biocontrol agent isolated from the roots of green pepper. The specific goals of the study were to characterize the strain and the antibiotics it produces. Standard microbiological methods identified the strain as a member of a species known to have biocontrol activity, and sophisticated biochemical analyses identified the antibiotics as being among those characteristic of the strain. Additional analyses revealed that antibiotic synthesis in this strain is regulated by Quorum sensing. The study is novel in demonstrating that a role for N-butanoyl homoserine lactone, which has not previously been shown to be involved in quorum sensing among strains of P. chlororaphis.
Technical Abstract: A new Pseudomonas strain, designated GP72, was isolated from green pepper rhizosphere and identified as a member of species Pseudomonas chlororaphis based on morphology; conventional biochemical and physiologic tests; Biolog GN system (Biolog Inc., Hayward, CA); and 16S rDNA sequence analysis. The secondary metabolites produced by this strain have shown broad-spectrum antifungal activity against various phytopathogens of agricultural importance in vitro. Two main antifungal substances produced by this strain proved to be phenazine-1-carboxylic acid and 2-hydroxyphenazine with further purification and structure elucidation based on ultraviolet-absorbent spectrum scanning, atmospheric pressure chemical ionization–mass spectrometry (APCI-MS) spectrum, and 1H,13C nuclear magnetic resonance spectrums. Strain GP72 could produce quorum-sensing signaling molecules of N-butanoyl-L-homoserine lactone and N-hexanoyl-L-homoserine lactone, which were found to accumulate with different quantities in King’s medium B and pigment producing medium, respectively.