Genetic analysis of the antifungal activity of a soilborne Pseudomonas aureofaciens strain

Abstract

Pseudomonas aureofaciens Q2-87 produces the antibiotic 2,4-diacetophloroglucinol (Phl), which inhibits Gaeumannomyces graminis var. tritici and other fungi in vitro. Strain Q2-87 also provides biological control of take-all, a root disease of wheat caused by this fungus. To assess the role of Phl in the antifungal activity of strain Q2-87, a genetic analysis of antibiotic production was conducted. Two mutants of Q2-87 with altered antifungal activity were isolated by site-directed mutagenesis with TnS. One mutant, Q2-87::Tn5-1, did not inhibit G. graminis var. tritici in vitro and did not produce Phl. Two cosmids were isolated from a genomic library of the wild-type strain by probing with the mutant genomic fragment. Antifungal activity and Phl production were coordinately restored in Q2-87::Tn5-1 by complementation with either cosmid. Mobilization of one of these cosmids into two heterologous Pseudomonas strains conferred the ability to synthesize Phl and increased their activity against G. graminis var. tritici, Pythium ultimum, and Rhizoctonia solani in vitro. Subcloning and deletion analysis of these cosmids identified a 4.8-kb region which was necessary for Phl synthesis and antifungal activity.

Isolation and characterization of a novel banana rhizosphere bacterium as fungal antagonist and microbial adjuvant in micropropagation of banana

“…DAPG has been well documented for its ability to suppress soil-borne fungal pathogens of root and seedling diseases. Some well-studied DAPG producing strains such as P. fluorescens CHAO, F113, Q2-87 and Q8r1-96 have been successfully used against black root rot of tobacco, crown and root rot of tomato, Pythium damping-off of cucumber and sugar beet, take-all of wheat and cyst nematode and soft rot of potato (Stutz et al 1986;Fenton et al 1992;Keel et al 1992;Vincent et al 1991;Harrison et al 1993;Cronin et al 1997;Duffy and Défago 1997;Raaijmakers and Weller 1998). Genetic studies demonstrate the role of DAPG in biological control, which is complemented by direct isolation of DAPG from the rhizosphere .…”

“…The broad-spectrum antimicrobial activity of DAPG produced by fluorescent pseudomonads has drawn great attention to agriculture because of its ability to suppress plant pathogens and play a key role in the biological control (Keel et al 1996; Thomashow and Weller 1996;Duffy and Défago 1997;Duffy et al 2004). DAPG-producing strains such as P. fluorescens Pf5, CHA0, F113, Q2-87, Q8r1-96 (Howell and Stipanovic 1980;Vincent et al 1991;Harrison et al 1993;Pierson and Weller 1994;Cronin et al 1997;Raaijmakers and Weller 1998;Duffy and Défago 1999) have been used to suppress the black root rot of tobacco, root rot of tomato, Pythium damping-off of cucumber and sugar beet, cyst nematode and soft rot of potato and take-all of wheat. Although antagonistic fluorescent pseudomonads associated with banana have been studied earlier (Banerjee and Langhe 1985;Sutra et al 2000), the role of DAPG or DAPG-producing bacterium for the suppression of banana wilts and root necrosis pathogens have not been reported so far.…”

Genetic diversity and biocontrol potential of fluorescent pseudomonads producing phloroglucinols and hydrogen cyanide from Swiss soils naturally suppressive or conducive to Thielaviopsis basicola-mediated black root rot of tobacco

“…In one such strain, designated CHA0, hydrogen cyanide (HCN) and 2,4-diacetylphloroglucinol (Phl; Keel et al, 1992) have been shown to be major determinants of the strain's biocontrol ability. HCN and, especially, Phl are also implicated in the biological control of soil-borne phytopathogens by other antagonistic fluorescent pseudomonads (Vincent et al, 1991;Fenton et al, 1992;Keel et al, 1992;Cronin et al, 1997;Ellis et al, 2000;Haas & Keel, 2003;Moënne-Loccoz & Défago, 2004). In addition, Phl 1 pseudomonads and Phl synthesis contribute to the monoculture decline of take-all disease of wheat caused by Gaeumannomyces graminis var.…”

Cosmopolitan distribution of phlD-containing dicotyledonous crop-associated biocontrol pseudomonads of worldwide origin

“…Phl is a polyketide displaying antifungal as well as antibacterial, antiviral, antihelminthic, antinematode and phytotoxic properties in vitro [11^14]. The use of Phl-minus derivatives of Pseudomonas £uorescens CHA0, F113 and Q2-87 in soil microcosms has shown the importance of Phl in disease suppression by the corresponding wildtype strains [3,13,15,16]. Moreover, Phl has been detected in the rhizosphere of plants colonized by Phl strains CHA0 (under gnotobiotic conditions; [13]) and Q2-87 (in non-sterile soil; [17]).…”