Frequency of Antibiotic-Producing Pseudomonas spp. in Natural Environments

TLDR

Phenazine‑1‑carboxylic acid and 2,4‑diacetylphloroglucinol are key antibiotics mediating biological control of soilborne plant pathogens by fluorescent *Pseudomonas* spp. The study aimed to develop primers and probes for specific detection of fluorescent *Pseudomonas* strains producing phenazine antibiotics or Phl. The authors designed these primers/probes and used colony hybridization followed by PCR to assess the frequency of Phl‑ and PCA‑producing fluorescent pseudomonads on wheat roots from suppressive and conducive soils. PCR and Southern hybridization revealed that Phl‑ and PCA‑biosynthetic genes are conserved worldwide, phenazine producers were absent, while Phl producers were abundant in suppressive soils and scarce in conducive soils, indicating Phl production may underlie natural take‑all suppression.

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 x 10(sup5) to 2 x 10(sup6) 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.