Biocontrol by Phenazine-1-carboxamide-Producing Pseudomonas chlororaphis PCL1391 of Tomato Root Rot Caused by Fusarium oxysporum f. sp. radicis-lycopersici

Abstract

Seventy bacterial isolates from the rhizosphere of tomato were screened for antagonistic activity against the tomato foot and root rot-causing fungal pathogen Fusarium oxysporum f. sp. radicis-lycopersici. One isolate, strain PCL1391, appeared to be an efficient colonizer of tomato roots and an excellent biocontrol strain in an F. oxysporum/tomato test system. Strain PCL1391 was identified as Pseudomonas chlororaphis and further characterization showed that it produces a broad spectrum of antifungal factors (AFFs), including a hydrophobic compound, hydrogen cyanide, chitinase(s), and protease(s). Through mass spectrometry and nuclear magnetic resonance, the hydrophobic compound was identified as phenazine-1-carboxamide (PCN). We have studied the production and action of this AFF both in vitro and in vivo. Using a PCL1391 transposon mutant, with a lux reporter gene inserted in the phenazine biosynthetic operon (phz), we showed that this phenazine biosynthetic mutant was substantially decreased in both in vitro antifungal activity and biocontrol activity. Moreover, with the same mutant it was shown that the phz biosynthetic operon is expressed in the tomato rhizosphere. Comparison of the biocontrol activity of the PCN-producing strain PCL1391 with those of phenazine-1-carboxylic acid (PCA)-producing strains P. fluorescens 2-79 and P. aureofaciens 30-84 showed that the PCN-producing strain is able to suppress disease in the tomato/F. oxysporum system, whereas the PCA-producing strains are not. Comparison of in vitro antifungal activity of PCN and PCA showed that the antifungal activity of PCN was at least 10 times higher at neutral pH, suggesting that this may contribute to the superior biocontrol performance of strain PCL1391 in the tomato/F. oxysporum system.

Phenazine antibiotics produced by fluorescent pseudomonads contribute to natural soil suppressiveness to Fusarium wilt

“…These two soils were the same as those used earlier to show the role of carbon and iron competition in soil suppressiveness to Fusarium wilts (Lemanceau et al, 1988). At this stage, the two structurally different antibiotics DAPG and phenazines were considered because of their established role in the activity of various Pseudomonas strains against pathogenic F. oxysporum (Georgakopoulos et al, 1994;Anjaiah et al, 1998;Chin-A-Woeng et al, 1998;Schouten et al, 2004) and, for DAPG-producing pseudomonads, because of their prevalence in a soil naturally suppressive to Fusarium wilt of peas (Landa et al, 2002). Molecular-based detection revealed that DAPGand phenazine-producing pseudomonads were present in the rhizosphere of flax and tomato plants grown in the wilt-suppressive soil.…”

“…For example, phenazine antibiotics were shown to play a key role in the biocontrol activity of several Pseudomonas species against F. oxysporum on diverse crops (Anjaiah et al, 1998;Chin-A-Woeng et al, 1998. Also the antibiotic 2,4-diacetylphloroglucinol (DAPG) has substantial activity against pathogenic F. oxysporum (Schouten et al, 2004), and populations of DAPG-producing pseudomonads were highly enriched in a soil naturally suppressive to Fusarium wilt of peas (Landa et al, 2002).…”

The role of antibiosis in the antagonism of different bacteria towards Helminthosporium solani, the causal agent of potato silver scurf

“…In confrontation assays on solid media, including when precultures on cellophane membranes were used, A. piechaudii, P. chlororaphis and S. griseus inhibited both mycelial growth and conidial germination of H. solani, suggesting that antibiosis is a contributor to the antagonistic effect of these bacteria through the diffusion of antifungal compounds into the medium. Alcaligenes piechaudii, P. chlororaphis and S. griseus had previously been shown to produce antibiotics (Assis et al 1998;Chin-A-Woeng et al 1998;Huddleston et al 1997), though not against H. solani.…”

Role of the phenazine-inducing protein Pip in stress resistance of Pseudomonas chlororaphis

“…Indeed phenazine-1-carboxamide (PCN) of Pseudomonas chlororaphis inhibits the growth of the fungal agent of tomato foot and root rot, Fusarium oxysporum f. sp. radicis lycopersici (Chin-A- Woeng et al, 1998). The phenazine pyocyanin produced by Pseudomonas aeruginosa is suggested to be involved in lung infection of cystic fibrosis patients (Caldwell et al, 2009).…”