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Title: Antibiotic production by Pseudomonas: Insights into biosynthesis, diversity, and environmental consequences.

item Thomashow, Linda
item Weller, David

Submitted to: ASM Conference
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2007
Publication Date: 8/26/2007
Citation: Thomashow, L.S., Mavrodi, V., Mavrodi, O.V., Weller, D.M. 2007. Antibiotic production by Pseudomonas: Insights into biosynthesis, diversity, and environmental consequences. ASM Conference. P.22.

Interpretive Summary:

Technical Abstract: Our current understanding of the biochemistry and environmental consequences of antibiotic biosynthesis by Pseudomonas is derived largely from studies of root-associated strains inhibitory to plant pathogens. Such strains often produce one or more antibiotics including pyoluteorin, pyrrolnitrin, 2,4-diacetylphloroglucinol (DAPG), and phenazine compounds. All phenazine-producing strains carry a conserved seven-gene core operon encoding the biosynthesis pathway for phenazine-1-carboxylic acid (PCA), the end product of P. fluorescens and a precursor for the more highly derivatized phenazines produced by species such as P. chlororaphis and P. aeruginosa. Derivatization is achieved via the products of “decorator” genes that may or may not be linked to the core operon. Despite the phenazine pigment pyocyanin having been reported over 150 years ago, only now are molecular and structural biology revealing the mechanism of phenazine biosynthesis, providing insight into strategies that may interfere with the synthesis of this virulence factor. In contrast to the phenazines, which are products of the shikimic acid pathway, DAPG is produced via a unique type III polyketide mechanism encoded by a four-gene operon that includes phlD, the product of which has homology to plant chalcone and stilbene synthases. DAPG-producing strains are associated with plants worldwide. Population densities of about 105 CFU/g of root or soil are sufficient to control take-all, an important root disease of cereals. Such population densities are present in soils with a long history of wheat cultivation, and are a key component in the natural suppressiveness of these soils to take-all. DAPG-producing strains include numerous distinct but closely related genotypes that differ in the aggressiveness with which they colonize host crops, revealing preferential genotype-by-host interactions apparently independent of DAPG production. The PCA and DAPG biosynthesis operons have not found together within natural isolates. However, we have constructed recombinant strains that synthesize both antibiotics and have monitored the stability, persistence, spread, and nontarget effects of the wild-type and recombinant strains in the growth chamber and the field. Our results have revealed metabolic costs to competitiveness associated with pyramiding pathways, unexpected interactions affecting antibiotic production, and host effects on the relative competitiveness of wild-type and recombinant strains.