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Title: Rhizoxin analogs, orfamide A and chitinase production contribute to the toxicity of Pseudomonas protegens strain Pf-5 to Drosophila melanogaster

item Loper, Joyce
item Henkels, Marcella
item RANGEL, LORENA - Oregon State University
item OLCOTT, MARIKA - Oregon State University
item WALKER, FRANCESCA - Oregon State University
item BOND, KISE - Oregon State University
item Kidarsa, Teresa
item Hesse, Cedar
item SNEH, BARUCH - Tel Aviv University
item Stockwell, Virginia
item TAYLOR, BARBARA - Oregon State University

Submitted to: Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2016
Publication Date: 4/30/2016
Citation: Loper, J.E., Henkels, M.D., Rangel, L.I., Olcott, M.H., Walker, F.L., Bond, K.L., Kidarsa, T.A., Hesse, C.N., Sneh, B., Stockwell, V.O., Taylor, B.J. 2016. Rhizoxin analogs, orfamide A and chitinase production contribute to the toxicity of Pseudomonas protegens strain Pf-5 to Drosophila melanogaster. Environmental Microbiology. 18(10):3509-3521. doi: 10.1111/1462-2920.13369.

Interpretive Summary: This manuscript evaluated the biological control bacterium Pseudomonas protegens Pf-5, which is known to suppress plant diseases and kill certain insects. We identified the reason why the bacterium kills the fruit fly Drosophila melangaster. Pf-5 was known previously to produce an insect toxin called FitD and a large number of biologically-active compounds ("natural products"). In this study, we generated a large set of mutants of Pf-5, each lacking the production of one compound or toxin, and compared each mutant to Pf-5 for oral toxicity to D. melanogaster. We discovered three factors produced by Pf-5 -- a chitinase and two natural products (rhizoxin and orfamide A)-- are required for full oral toxicity to D. melanogaster. The insect toxin FitD had no detectable role against D. melanogaster even though it is known to be the primary reason that Pf-5 kills lepidopteran insects. These results show that different factors are responsible for Pf-5's toxicity against different insects. We also showed that rhizoxin, which had no known insect toxicity previously, is the primary factor responsible for Pf-5's toxicity to D. melanogaster.

Technical Abstract: Pseudomonas protegens strain Pf-5 is a soil bacterium that was first described for its activity in biological control of plant diseases and has since been shown to be lethal to certain insects. Among these is the fruit fly Drosophila melanogaster, a well-established model organism for studies evaluating the molecular and cellular basis of the immune response to bacterial challenge. Pf-5 produces the insect toxin FitD, but a 'fitD mutant of Pf-5 retained full toxicity against D. melanogaster in a non-invasive feeding assay, indicating that FitD is not a major determinant of Pf-5’s oral toxicity against this insect. Pf-5 also produces a broad spectrum of exoenzymes and natural products with antibiotic activity, whereas a mutant with a deletion in the global regulatory gene gacA produces none of these exoproducts and also lacks toxicity to D. melanogaster. In this study, we made use of a panel of Pf-5 mutants having single or multiple mutations in the biosynthetic gene clusters for seven natural products and two exoenzymes that are produced by the bacterium under the control of gacA. Our results demonstrate that rhizoxin, orfamide A and chitinase production are required for full oral toxicity of Pf-5 against D. melanogaster, with rhizoxin being the primary determinant.