Pyoluteorin is a secondary metabolite produced by the biological control organism Pseudomonas fluorescens Pf-5, a rhizosphere bacterium. Pyoluteorin shows no toxicity to seed- and root-rotting plant pathogens. Pyoluteorin production is influenced by positive autoregulation. Addition of pyoluteorin to liquid cultures of Pf-5 enhanced pyoluteorin production.

Pyoluteorin functions as a signal molecule negatively regulating additional secondary metabolites produced by Pseudomonas [1]. The pyoluteorin contributes to the biological control of soilborne plant diseases by some strains of Pseudomonas fluorescens, including Pf-5. Pyoluteorin induces its own productionand represses the other’s production [2]. Depending on the plant, pyoluteorin production plays an important role in the suppression of damping-off by strain CHA0 without being a major mechanism in disease suppression [3].

References:
[1] Brodhagen M, Henkels M D, Loper J E.  Positive autoregulation and signaling properties of pyoluteorin, an antibiotic produced by the biological control organism Pseudomonas fluorescens Pf-5[J]. Applied and environmental microbiology, 2004, 70(3): 1758-1766.
[2] Kidarsa T A, Goebel N C, Zabriskie T M, et al.  Phloroglucinol mediates cross‐ alk between the pyoluteorin and 2, 4‐diacetylphloroglucinol biosynthetic pathways in Pseudomonas fluorescens Pf‐5[J]. Molecular microbiology, 2011, 81(2): 395-414.
[3] Maurhofer M, Keel C, Haas D, et al.  Pyoluteorin production byPseudomonas fluorescens strain CHA0 is involved in the suppression ofPythium damping-off of cress but not of cucumber[J]. European journal of plant pathology, 1994, 100(3): 221-232.