Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2008
Publication Date: 5/10/2008
Citation: Loper, J.E., Henkels, M.D., Shaffer, B.T., Valeriote, F.A., Gross, H. 2008. Isolation and identification of rhizoxin derivatives from Pseudomonas fluorescens Pf-5 using a genomic mining strategy. Applied and Environmental Microbiology. 74(10):3085-3093. Interpretive Summary: This manuscript describes the identification of new chemical compounds (natural products) produced by a microorganism called Pseudomonas fluorescens strain Pf-5, which was isolated from soil. We used a new approach to identify unknown natural products from organisms whose genome sequences are known. The approach begins with a thorough analysis of nucleotide sequences to predict components of the final chemical structure, proceeds by identifying conditions where the genes are expressed, and uses chemical separation and analysis methods to purify and determine the structure of the unknown chemical. We discovered that Pseudomonas fluorescens Pf-5 produces five analogs of rhizoxin, a natural product known to be toxic to fungi, some plants, and to tumor cells. One of the five analogs is a new compound, which has not been found before. We tested the toxicity of all five analogs, and found that two of the compounds, including the new one, were most toxic against a fungal and an Oomycete plant pathogen, three plant species, and human cancer cells. These results extend our knowledge of strain Pf-5, which can suppress plant diseases by producing antibiotics toxic against plant pathogens.
Technical Abstract: The products synthesized from a hybrid polyketide synthase/nonribosomal peptide synthetase gene cluster in the genome of Pseudomonas fluorescens Pf-5 were identified using a genomics-guided strategy involving insertional mutagenesis and subsequent metabolite profiling. Five analogs of rhizoxin, a 16-membered macrolide with antifungal, phytotoxic, and antitumor activities, were produced by Pf-5 but not by a mutant with an insertion in the PKS/NRPS gene cluster. The five rhizoxin analogs, one of which has not been described previously, were differentially toxic to two agriculturally-important plant pathogens, Botrytis cinerea and Phytophthora ramorum, and human tumor cell lines. The rhizoxin analogs also caused swelling of rice roots, a symptom characteristic of rhizoxin itself, but were less toxic to pea and cucumber roots.