|Zabriskie, T. Mark|
Submitted to: Molecular Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2011
Publication Date: 7/1/2011
Citation: Kidarsa, T.A., Goebel, N.C., Zabriskie, T., Loper, J.E. 2011. Phloroglucinol mediates crosstalk between the pyoluteorin and 2,4-diacetylphloroglucinol biosynthetic pathways in Pseudomonas fluorescens Pf-5. Molecular Microbiology. 81(2):395-414. Interpretive Summary: Biological control is a promising and environmentally-friendly approach for the management of plant diseases. Certain strains of Pseudomonas fluorescens live on root surfaces and protect roots from infection by plant pathogens that live in the soil. These bacteria produce antibiotics that kill fungal or Oomycete plant pathogens. Factors that influence the production of these antibiotics also influence the success of biological control. In this study, we focus on the root-inhabiting bacterium P. fluorescens Pf-5, which produces many different antibiotics. We show that in Pf-5 the compound phloroglucinol, which is an intermediate in the biosynthesis of the antibiotic 2,4-diacetylphloroglucinol, influences the production of a second antibiotic, pyoluteorin. At very low concentrations, phloroglucinol is required for pyoluteorin production, but at higher concentrations, phloroglucinol inhibits pyoluteorin production. These results are important because they show that antibiotics, or an intermediate in antibiotic production such as phloroglucinol, can function as signaling molecules, in addition to their known roles in suppressing microbial growth. Also, the results highlight a new factor influencing biological control of plant disease, which could open the door to future studies aiming to improve biological control for use in agriculture.
Technical Abstract: The antibiotics pyoluteorin and 2,4-diacetylphloroglucinol (DAPG) are involved in the biological control of certain soil-borne diseases by some strains of Pseudomonas fluorescens, including P. fluorescens Pf-5. These secondary metabolites also act as signaling molecules with each compound reported to induce its own production and repress each other’s production. In this study, we show that the biosynthetic intermediate phloroglucinol (PG) is required at nanomolar concentrations for pyoluteorin production in Pf-5. At higher concentrations, PG is responsible for the inhibition of pyoluteorin production previously attributed to DAPG. DAPG had no effect on pyoluteorin production, and monoacetylphloroglucinol showed both stimulatory and inhibitory activities but at concentrations 100-fold greater than the levels of PG required for similar effects. Resorcinol, a compound structurally-related to PG, showed inhibitory but not stimulatory effects on pyoluteorin production. We also demonstrate that a PhlD homolog encoded by a gene adjacent to the pyoluteorin biosynthetic gene cluster of Pseudomonas aeruginosa strains LESB58, PACS171b, and PACS88 synthesizes PG and can stimulate pyoluteorin production when introduced into Pf-5. Bioinformatic analyses show that the dual role of PhlD in the biosynthesis of DAPG and the regulation of pyoluteorin production could have arisen within the Pseudomonads during the assembly of these biosynthetic gene clusters from genes and gene subclusters having diverse origins.