Frequency of Antibiotic-Producing Pseudomonas spp. in Natural Environments

Abstract

The antibiotics phenazine-1-carboxylic acid (PCA) and 2,4-diacetylphloroglucinol (Phl) are major determinants of biological control of soilborne plant pathogens by various strains of fluorescent Pseudomonas spp. In this study, we described primers and probes that enable specific and efficient detection of a wide variety of fluorescent Pseudomonas strains that produce various phenazine antibiotics or Phl. PCR analysis and Southern hybridization demonstrated that specific genes within the biosynthetic loci for Phl and PCA are conserved among various Pseudomonas strains of worldwide origin. The frequency of Phl-and PCA-producing fluorescent pseudomonads was determined on roots of wheat grown in three soils suppressive to take-all disease of wheat and four soils conducive to take-all by colony hybridization followed by PCR. Phenazine-producing strains were not detected on roots from any of the soils. However, Phl-producing fluorescent pseudomonads were isolated from all three take-all-suppressive soils at densities ranging from approximately 5 ؋ 10 5 to 2 ؋ 10 6 CFU per g of root. In the complementary conducive soils, Phl-producing pseudomonads were not detected or were detected at densities at least 40-fold lower than those in the suppressive soils. We speculate that fluorescent Pseudomonas spp. that produce Phl play an important role in the natural suppressiveness of these soils to take-all disease of wheat.

Polymorphisms within the prnD and pltC genes from pyrrolnitrin and pyoluteorin-producing Pseudomonas and Burkholderia spp.

“…Pseudomonas spp. harboring phlD, one of the genes involved in biosynthesis of the antibiotic 2,4-DAPG, were detected at densities similar to those reported by other authors for the wheat and maize rhizosphere [13,63]. The occurrence of relatively higher populations of 2,4-DAPG-producing Pseudomonas spp.…”

Investigations of the structure and function of bacterial communities associated with Sphagnum mosses

“…In addition, the production of antifungal antibiotics was detected for a high proportion of bacterial isolates. However, only for a few isolates the genes encoding for enzymes involved in the biosynthesis of antibiotics that are well-known for plant-associated antagonists (Raaijmakers et al, 1997) were detected. Two Burkholderia isolates were tested positive for the pyrrolnitrin biosynthetic gene prnD.…”

Degradation of pathogen quorum-sensing molecules by soil bacteria: a preventive and curative biological control mechanism

“…Q2-87 we showed that AHL degradation was a mechanism for controlling bacterial plant diseases as e¡ective as or better than phenazine and 2,4-diacetylphloroglucinol antibiotic production. Our ¢nding of AHL degradation as a novel mechanism of plant disease suppression opens the door for targeted selection of new wild-type strains that may be even more e¡ective at degrading pathogen autoinducers, much as earlier work demonstrating the important role of antibiotic production in biocontrol has led to designing molecular probes used to streamline the screening process for new biocontrol agents [44]. The aiiA gene responsible for AHL degradation in Bacillus sp.…”