Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 20, 2000
Publication Date: N/A
Interpretive Summary: A classic biological control agent is known to produce the antibiotic phenazine-1-carboxylic acid (PCA) as its primary means of suppressing take-all root disease of wheat. In addition to PCA, we have now discovered another metabolite in a defined liquid production culture of strain 2-79. The metabolite was isolated, purified, and identified as 2-acetamidophenol (AAP). The accumulations of AAP and PCA in liquid cultures were positivel correlated. This is the first report of AAP production by the classic biological control strain P. fluorescens 2-79. This finding is pertinent to our understanding of the metabolic pathways fundamental to the ability of strain 2-79 to efficiently accomplish biological control, and it is expected to impact the design of efficacious commercial seed inoculants of phenazine-producing bacteria for take-all control.
Technical Abstract: Pseudomonas fluorescens strain 2-79 (NRRL B-15132) is a classic biological control agent which is known to produce phenazine-1-carboxylic acid (PCA) as its primary means of suppressing take-all disease of wheat. In addition to PCA, an unknown metabolite was discovered by thin-layer chromatography (TLC) in a defined liquid production culture of strain 2-79. The 1**H and **13C nuclear magnetic resonance and electron impact mass spectra indicate the identity of the purified compound to be 2-acetamidophenol (AAP). Using reversed-phase high performance liquid chromatography (HPLC), the accumulations of AAP and PCA in cultures of strain 2-79 were measured to reach 0.05 g/L and 1 g/L, respectively. The accumulations of AAP and PCA in liquid cultures were linearly correlated (P<0.001), as shown by studies of cultures stimulated to yield varying levels of PCA by controlling levels of oxygen transfer, pH, and growth medium composition. In this study, oxygen limitation, a defined amino-acid-free medium, and neutral pH stimulated maximal production of both AAP and PCA. Furthermore, a mutant strain of 2-79 unable to produce PCA [2A40 2-79(phz-)] did not accumulate AAP. These findings indicate that AAP and PCA are likely to share a common segment of pathway steps during biosynthesis. This is the first report of AAP production by the classic biological control strain P. fluorescens 2-79. Possible routes of AAP production are discussed relative to current knowledge of the phenazine biosynthetic pathway of strain 2-79. The relevance of AAP to the design of commercial seed inoculants of phenazine-producing bacteria for controlling wheat take-all is also considered.