1887

Abstract

PA23 is a biocontrol agent capable of protecting canola from stem rot disease caused by the fungus . The focus of the current study was to elucidate the role of the transcriptional regulator ANR in the biocontrol capabilities of this bacterium. An mutant was created, PA23, that was devoid antifungal activity. In other pseudomonads, ANR is essential for regulating HCN production. Characterization of PA23 revealed that, in addition to HCN, ANR controls phenazine (PHZ), pyrrolnitrin (PRN), protease and autoinducer (AHL) signal molecule production. In gene expression studies, , , and were found to be downregulated, consistent with our endproduct analysis. Because the phenotype of PA23 closely resembles that of quorum sensing (QS)-deficient strains, we explored whether there is a connection between ANR and the PhzRI QS system. Both and are positively regulated by ANR, whereas PhzR represses transcription. Complementation of PA23 with pUCP-, C-HSL or both yielded no change in phenotype. Conversely, PA23 harbouring pUCP23- exhibited partial-to-full restoration of antifungal activity, HCN, PRN and AHL production together with , , and expression. PHZ and protease production remained unchanged indicating that ANR can complement the QS-deficient phenotype with respect to some but not all traits. Our experiments were conducted at atmospheric O levels underscoring the fact that ANR has a profound effect on PA23 physiology under aerobic conditions.

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2016-12-21
2020-01-29
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