Submitted to: Gene
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 7, 1997
Publication Date: N/A
Interpretive Summary: The biological control of plant pathogens provides an alternative treatment for plant diseases that are not adequately controlled by current agricultural practices. Pseudomonas fluorescens PF-5 is a promising biological control agent that produces several antifungal metabolites that contribute to its biological control properties. Our current research focuses on the production of one of these metabolites, pyoluteorin. Previous research within our lab has identified several factors that affect pyoluteorin production. In this study, we describe two genes that are required for the synthesis of pyoluteorin. The proteins encoded by these genes are similar to other polyketide synthases that have been reported in the literature and have provided insight to the metabolic pathways operating within P. fluorescens Pf-5. Polyketide synthases have captured the attention of many researchers because the metabolites produced by these enzymes are either economically important or could be exploited in the production of potentially valuable chemicals. Furthermore, the detailed understanding of pyoluteorin production that is unfolding may lead to the development of a more effective biological control agent.
Technical Abstract: Pyoluteorin is a chlorinated metabolite of mixed polyketide/amino acid origin produced by the biocontrol agent Pseudomonas fluorescens Pf-5. Pyoluteorin inhibits growth of oomycete fungi, including the plant pathogen Pythium ultimum. Sequence analysis of a gene cluster required for pyoluteorin biosynthesis (Kraus and Loper, 1995. Appl.environ. Microbial.61:849-854.) has identified two genes whose deduced peptide sequences exhibit characteristics of both fungal and bacterial Type I polyketide synthases (PKSs). The pyoluteorin PKS does not contain a loading domain that is typically present in bacterial Type I PKSs. Furthermore, this PKS possesses an acyltransferase domain that does not contain the conserved residues surrounding the active-site motif typically found in domains of similar function. Based on the organization of the functional domains within the pyoluteorin PKS, we propose a biosynthetic pathway analogous to nonaromatic polyketide biosynthesis within the actinomycete bacteria that is responsible for the formation of the resorcinol moiety of pyoluteorin.