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Revised structure for the phenazine antibiotic from Pseudomonas fluorescens 2-79 (NRRL B-15132)
P G Brisbane1, L J Janik, M E Tate
1Division of Soils, Commonwealth Scientific and Industrial Research Organisation, Glen Osmond, South Australia.
Abstract:
A phenazine antibiotic (mp, 243 to 244 degrees C), isolated in a yield of 134 micrograms/ml from cultures of Pseudomonas fluorescens 2-79 (NRRL B-15132), was indistinguishable in all of its measured physicochemical (melting point, UV and infrared spectra, and gas chromatography-mass spectrometry data) and biological properties from synthetic phenazine-1-carboxylic acid. Gurusiddaiah et al. (S. Gurusiddaiah, D. M. Weller, A. Sarkar, and R. J. Cook, Antimicrob. Agents Chemother. 29:488-495, 1986) attributed a dimeric phenazine structure to an antibiotic with demonstrably similar properties obtained from the same bacterial strain. Direct comparison of the physicochemical properties of the authentic antibiotic obtained from D. M. Weller with synthetic phenazine-1-carboxylic acid and with the natural product from the present study established that all three samples were indistinguishable within the experimental error of each method. No evidence to support the existence of a biologically active dimeric species was obtained. Phenazine-1-carboxylic acid has a pKa of 4.24 +/- 0.01 (25 degrees C; I = 0.09), and its carboxylate anion shows no detectable antimicrobial activity compared with the active uncharged carboxylic acid species. These data suggest that phenazine-1-carboxylic acid is probably not an effective biological control agent for phytopathogens in environments with a pH greater than 7.
Insights
This study identified phenazine-1-carboxylic acid from Pseudomonas fluorescens, finding it indistinguishable from synthetic versions. The research found no evidence for a dimeric form and suggests limited efficacy against phytopathogens above pH 7.
Area of Science:
- Microbiology
- Natural Product Chemistry
- Biochemistry
Background:
- Pseudomonas fluorescens produces phenazine antibiotics.
- Previous research suggested a dimeric phenazine structure from this bacterium.
- The biological activity of phenazine derivatives is pH-dependent.
Purpose of the Study:
- To characterize the phenazine antibiotic produced by Pseudomonas fluorescens 2-79.
- To compare the natural product with synthetic phenazine-1-carboxylic acid and a previously reported dimeric structure.
- To investigate the antimicrobial activity of phenazine-1-carboxylic acid and its anion.
Main Methods:
- Isolation and purification of the antibiotic from bacterial cultures.
- Physicochemical characterization using melting point, spectroscopy, and chromatography-mass spectrometry.
- Direct comparison of natural and synthetic compounds.
- Determination of pKa and antimicrobial activity at different pH levels.
Main Results:
- The isolated antibiotic was identical to synthetic phenazine-1-carboxylic acid.
- No evidence supported the existence of a biologically active dimeric phenazine species.
- Phenazine-1-carboxylic acid's carboxylate anion showed no antimicrobial activity.
Conclusions:
- Phenazine-1-carboxylic acid is the active antimicrobial compound produced by Pseudomonas fluorescens 2-79.
- The previously proposed dimeric structure was not supported by this study.
- Phenazine-1-carboxylic acid is unlikely to be effective for biological control of phytopathogens in environments with pH > 7.