The genotypic diversity of antibiotic-producing Pseudomonas spp. provides an enormous resource for identifying strains that are highly rhizosphere competent and superior for biological control of plant diseases. In this study, a simple and rapid method was developed to determine the presence and genotypic diversity of 2,4-diacetylphloroglucinol (DAPG)-producing Pseudomonas strains in rhizospher...

A real-time PCR SYBR green assay was developed to quantify populations of 2,4-diacetylphloroglucinol (2,4-DAPG)-producing (phlD+) strains of Pseudomonas fluorescens in soil and the rhizosphere. Primers were designed and PCR conditions were optimized to specifically amplify the phlD gene from four different genotypes of phlD+ P. fluorescens. Using purified genomic DNA and genomic DNA extracted f...

PhlD, a type III polyketide synthase from Pseudomonas fluorescens, catalyzes the synthesis of phloroglucinol from three molecules of malonyl-CoA. Kinetic analysis by direct measurement of the appearance of the CoASH product (k(cat) = 24 +/- 4 min(-1) and Km = 13 +/- 1 microM) gave a k(cat) value more than an order of magnitude higher than that of any other known type III polyketide synthase. Ph...

ABSTRACT Analyses of multiple field experiments indicated that the incidence and relative abundance of root-colonizing phlD+ Pseudomonas spp. were influenced by crop rotation, tillage, organic amendments, and chemical seed treatments in subtle but reproducible ways. In no-till corn plots, 2-year rotations with soybean resulted in plants with approximately twofold fewer phlD+ pseudomonads per gr...

ABSTRACT Pseudomonas species that produce 2,4-diacetylphloroglucinol (2,4-DAPG) play a significant role in the suppression of fungal root pathogens in the rhizosphere of crop plants. To characterize the abundance and diversity of these functionally important bacterial populations, we developed a rapid polymerase chain reaction (PCR)-based assay targeting phlD, an essential gene in the phloroglu...

ABSTRACT Fluorescent Pseudomonas spp. that produce 2,4-diacetylphloroglucinol (2,4-DAPG) have biocontrol activity against damping-off, root rot, and wilt diseases caused by soilborne fungal pathogens, and play a key role in the natural suppression of Gaeumannomyces graminis var. tritici, known as take-all decline. Diversity within phlD, an essential gene in the biosynthesis of 2,4-DAPG, was stu...

Substantial concentrations of phloroglucinol were synthesized by Pseudomonas fluorescens Pf-5 expressing the plasmid-localized phlACBDE gene cluster responsible for biosynthesis of 2,4-diacetylphloroglucinol. Expression in Escherichia coli of a single gene in this cluster, P. fluorescens Pf-5 phlD, led to extracellular accumulation of phloroglucinol. Purification of PhlD to homogeneity afforded...