Two Novel MvaT-Like Global Regulators Control Exoproduct Formation and Biocontrol Activity in Root-Associated Pseudomonas fluorescens CHA0

Abstract

Pseudomonas fluorescens CHA0 protects various crop plants against root diseases caused by pathogenic fungi. Among a range of exoproducts excreted by strain CHA0, the antifungal compounds 2,4-diacetylphloroglucinol (DAPG) and pyoluteorin (PLT) are particularly relevant to the strain's biocontrol potential. Here, we report on the characterization of MvaT and MvaV as novel regulators of biocontrol activity in strain CHA0. We establish the two proteins as further members of an emerging family of MvaT-like regulators in pseudomonads that are structurally and functionally related to the DNA-binding protein H-NS. In mvaT and mvaV in frame-deletion mutants of strain CHA0, PLT production was enhanced about four- and 1.5-fold, respectively, whereas DAPG production remained at wild-type levels. Remarkably, PLT production was increased up to 20-fold in an mvaT mvaV double mutant. DAPG biosynthesis was almost completely repressed in this mutant. The effects on antibiotic production could be confirmed by following expression of gfp-based reporter fusions to the corresponding biosynthetic genes. MvaT and MvaV also influenced levels of other exoproducts, motility, and physicochemical cell-surface properties to various extents. Compared with the wild type, mvaT and mvaV mutants had an about 20% reduced capacity (in terms of plant fresh weight) to protect cucumber from a root rot caused by Pythium ultimum. Biocontrol activity was nearly completely abolished in the double mutant Our findings indicate that MvaT and MvaV act together as further global regulatory elements in the complex network controlling expression of biocontrol traits in plant-beneficial pseudomonads.

Efficacy of Certain Bio-Agents and Plant Extracts against Late Blight (Phytophthora infestans) of Tomato (Lycopersicon esculentum L.)

“…Maximum yield (q/ha) was recorded in treatment P. fluorescens @ 5g/l (223.10 q/ha) followed by T. viride @ 5g/l (213.36 q/ha) as compared to treated control (244.50 q/ha) and untreated control (103.50 q/ha). Islam and Faruq (2008), Manoranjitham et al, (1999), Bunker and Mathur (2001), Haas and De´fago (2005), Baehler et al, (2006) and Dubuis et al, (2007). Similar findings have also been reported by Karegowda et al, (2009) who found that T. viride and T. harzianum overgrew and suppressed the growth of Phytophthora capsici, Dennis and Webster, (1971) reported that Trichoderma spp.…”

Bacterial Subfamily of LuxR Regulators That Respond to Plant Compounds

“…P. fluorescens strains were added as a suspension (5 ml per flask) of washed cells to give 10 7 CFU/g of soil. Seedlings were covered with nontreated soil, and the flasks were sealed and incubated as specified by Baehler et al (4).…”

Predators promote defence of rhizosphere bacterial populations by selective feeding on non-toxic cheaters

“…A 1.5-kb MluI-HindIII fragment from the resulting plasmid carrying the P tac -dsred.T3_S4T fusion was then cloned into the mini-Tn7-Gm carrier plasmid, pME3280b (Zuber et al, 2003). The construct obtained, pME7160, and the Tn7 transposition helper plasmid pUX-BF13 (Bao et al, 1991) were coelectroporated (Baehler et al, 2006) into the recipient strain CHA0. The gacS mutant CHA19 (Zuber et al, 2003) was tagged with a green fluorescent protein as follows: a mini-Tn7-gfp2 cassette carrying the gfpmut3 gene controlled by a modified P tac promoter (Koch et al, 2001) was introduced into the chromosome of strain CHA19 using the transposition helper pUX-BF13, giving CHA19-g.…”