Phenazines are not essential for Pseudomonas chlororaphis  PA23 biocontrol of Sclerotinia sclerotiorum, but  do play a role in biofilm formation

Abstract

Pseudomonas chlororaphis strain PA23 is a biocontrol agent capable of suppressing disease caused by the fungal pathogen Sclerotinia sclerotiorum. This bacterium produces the diffusible antibiotics phenazine-1-carboxylic acid, 2-hydroxyphenazine and pyrrolnitrin (PRN). Because the individual contribution of these antibiotics to PA23 biocontrol has not been defined, mutants deficient in the production of phenazine (PHZ), PRN or both antibiotics were created. Analysis of the PHZ mutant revealed enhanced antifungal activity in vitro and wild-type levels of Sclerotinia disease suppression. Conversely, the PRN- and the PRN/PHZ-deficient strains exhibited decreased antifungal activity in vitro and markedly reduced the ability to control Sclerotinia infection of canola in the greenhouse. These findings suggest that PRN is the primary antibiotic mediating biocontrol of this pathogen. Analysis of prnA-lacZ and phzA-lacZ transcriptional fusions revealed that PRN and PHZ are not subject to autoregulation; moreover, they do not cross-regulate each other. However, HPLC showed a twofold increase in PRN levels in the PHZ(-) background. Finally, PHZ, but not PRN production, is involved in biofilm development in P. chlororaphis PA23.

The PhzI/PhzR quorum-sensing system is required for pyrrolnitrin and phenazine production, and exhibits cross-regulation with RpoS in Pseudomonas chlororaphis PA23

“…The sequence of the phzI and phzR genes was determined through a primer walking strategy using a Tn5 XhoI rescue clone previously isolated in our laboratory (Selin et al, 2010). This plasmid contains a portion of the phz biosynthetic locus (phzABCDE) and approximately 17 kb of upstream DNA.…”

“…Pseudomonas chlororaphis strain PA23 has shown excellent biocontrol of sclerotinia stem rot of canola caused by the fungal pathogen Sclerotinia sclerotiorum (Fernando et al, 2007;Savchuk & Dilantha Fernando, 2004). Strain PA23 produces a number of secondary metabolites, including phenazine (PHZ), pyrrolnitrin (PRN), HCN, proteases, lipases and siderophores, some of which have been shown to contribute to antagonism (Poritsanos et al, 2006;Zhang et al, 2006;Selin et al, 2010).…”

Antifungal activity of Pseudomonas chlororaphis Q16 against Sclerotinia sclerotiorum isolated from different medicinal plants

“…Iako PA23 produkuje difuzibilne antibiotike fenazin-1-karboksilnu kiselinu, 2-hidroksifenazin i pirolnitrin (PRN), koji suprimiraju S. sclerotiorum, primarni antibiotik odgovoran za biokontrolu ovog patogena je PRN, koji se sintetiše u dvostruko većoj koncentraciji kod PHZ(-) mutanata, ali ne učestvuje u produkciji biofilma. PHZ, pored antibiotskog delovanja na rast S. sclerotiorum, deluju stimulativno na formiranje biofilma (Poritsanos et al, 2006;Selin et al, 2010). Među sekundarnim metabolitima koje ovaj soj sintetiše su litički enzimi-lipaze i proteaze, cijanovodonik i siderofore koji doprinose antagonizmu prema S. sclerotiorum (Poritsanos et al, 2006;Zhang et al, 2006;Selin et al, 2010).…”

“…PHZ, pored antibiotskog delovanja na rast S. sclerotiorum, deluju stimulativno na formiranje biofilma (Poritsanos et al, 2006;Selin et al, 2010). Među sekundarnim metabolitima koje ovaj soj sintetiše su litički enzimi-lipaze i proteaze, cijanovodonik i siderofore koji doprinose antagonizmu prema S. sclerotiorum (Poritsanos et al, 2006;Zhang et al, 2006;Selin et al, 2010). Eksperimenti u polju su potvrdili da P. chlororaphis PA23 efikasno sprečava trulež stabljike uljane repice izazvanu S. sclerotiorum (Fernando et al, 2007;Savchuk and Dilantha Fernando, 2004).…”

Biological control of the soil-borne fungal pathogen Sclerotinia sclerotiorum –– a review

“…In most cases Pseudomonas showed multiple mechanisms in the biocontrol of diseases caused by S. sclerotiorum. Zazzerini 1987;Zhang and Fernando 2004a;Chitrampalam et al 2008;Hu et al 2011;Zeng et al 2012a, b;Monteiro et al 2013;Hu et al 2014;Kamal et al 2015 Bacillus megaterium Hu et al 2013;Hu et al 2014 Bacillus amyloliquefaciens Fernando et al 2007 Bacillus cereus Zazzerini 1987;Kamal et al 2015 Erwinia herbicola (Pantoea agglomerans) Godoy et al 1990b;Yuen et al 1994 Pseudomonas chlororaphis Zhang and Fernando 2004b;Savchuk and Fernando 2004;Fernando et al 2007;Selin et al 2010 Pseudomonas fluorescens Bin et al 1991;Expert and Digat 1995 Pseudomonas putida Expert and Digat 1995…”