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Insect Toxicity in Plant Associated Fluorescent Pseudomonads

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Insect Toxicity in Plant Associated Fluorescent Pseudomonads Faculteit Bio-ingenieurswetenschappen Academiejaar 2012 – 2013 Insect toxicity in plant associated fluorescent pseudomonads Insecten toxiciteit bij plant-geassocieerde fluorescente pseudomonaden Thomas Van den haute Promotors: Prof. Dr. ir. Monica Höfte, Prof. Dr. ir. Patrick De Clercq Tutors: Prof. Dr. ir. Monica Höfte, Dr. Chien-Jui Huang Masterproef voorgelegd tot het behalen van de graad van Master in de Bio- Ingenieurswetenschappen: Landbouwkunde ii Faculteit Bio-ingenieurswetenschappen Academiejaar 2012 – 2013 Insect toxicity in plant associated fluorescent pseudomonads Insecten toxiciteit bij plant-geassocieerde fluorescente pseudomonaden Thomas Van den haute Promotors: Prof. Dr. ir. Monica Höfte, Prof. Dr. ir. Patrick De Clercq Tutors: Prof. Dr. ir. Monica Höfte, Dr. Chien-Jui Huang Masterproef voorgelegd tot het behalen van de graad van Master in de Bio- Ingenieurswetenschappen: Landbouwkunde De auteur en de promotors geven de toelating deze masterproef voor consultatie beschikbaar te stellen en delen ervan te kopiëren voor persoonlijk gebruik. Elk ander gebruik valt onder de beperkingen van het auteursrecht, in het bijzonder met betrekking tot de verplichting uitdrukkelijk de bron te vermelden bij het aanhalen van resultaten uit deze masterproef. Gent, Juni 2013 De auteur: Thomas Van den haute De promotors: Prof. Dr. ir. M. Höfte Prof. Dr. ir. P. De Clercq i PREFACE Mijn masterpoef, het pronkstuk van een 6 jaar durende studie, is eindelijk af. Nu ik dit tot een goed einde bracht, sluit ik naast mijn boeken ook een hoofdstuk af in mijn levensloop. “De beste tijd uit u leven”, het studentenleven, is nu voorbij. Een tijd getekend door dieptepunten, maar vooral heel veel hoogtepunten: het zenuwslopende afwachten op de allereerste resultaten, het maken van vele nieuwe vrienden, een eerste keer buizen, de onstuimige feestjes, het leren kennen van mijn stad Gent vanuit een andere oogpunt, liefdesperikelen, het eerste mondelijke examen, de vele studietrips, in het oog van de storm zitten in Kievit, 6 maanden overleven in het zonnige Córdoba, mijn Brits en labotechnieken bijschaven in Reading, … Te veel om op te noemen. Dit alles had ik echter nooit kunnen doen ware het niet van een aantal bijzondere mensen. In de eerste plaats wil ik mijn beide promotors, prof. dr. ir. Höfte en prof. dr. ir. De Clercq, bedanken voor deze kans die ik heb gekregen en hopelijk met beide handen heb gegrepen. Het was niet alleen een professionele verrijking aan labo-ervaring maar ook een harde leerschool in geduld, concentratie en werklust. Dankzij jullie nauwe opvolging bleef ik met de voetjes op de grond en verloor ik mezelf niet in m’n chaotische gedachtegang. Secondly I wish to express my greatest gratitude to my tutor Huang, who guided me through the reluctant ways of Pseudomonas. Our endless discussions were an enormous source of inspiration and it kept me motivated. I also wanted to thank everyone from the lab of Phytopathology for helping me with my many questions. Ook had ik graag het labo van Agrozoölogie willen bedanken, en dan vooral Leen en Didier, voor hun hulp bij het kweken van mijn behoeftige insectjes. Vervolgens wou ik mijn medethesisstudentjes bedanken. Lien, Charissa, Ellen, ondanks ieders probleempjes (plantjes vergeten water geven, ontploffende flessen, brandwonden en mislukte proeven) waren we er voor elkaar en hadden we altijd tijd voor ’n koffiepauze of ’n leuke babbel. Ik wens iedereen veel succes toe, maar eerst een welverdiende vakantie. Tot slot, de waarheid overtreft het cliché, ware het niet dankzij de oneindige steun van mijn ouders en grootouders, was ik nooit geraakt waar ik nu sta. Mama en papa, jullie boden me de kans te studeren, jullie bleven me motiveren om verder te doen en we amuseerden ons rot. Nu hoop ik jullie te kunnen bewijzen dat het geen “six years down the drain” waren. Het was in ieder geval een onvergetelijke rit waar we geluk en vreugde deelden. ii SUMMARY Ever since the first descriptions of plant-protecting rhizobacteria, microorganisms with specific qualities have been proposed as valuable alternatives to conventional crop protection measures, mostly involving synthetic chemicals. Research involving the control or suppression of soil-borne fungal and bacterial pathogens had risen substantially. Recently, insect pest control by microorganisms was readily received for research. After the prominent discoveries of insecticidal toxins from Bacillus thuringiensis and from the nematode- associated Photorhabdus spp. and Xenorhabdus spp., certain fluorescent pseudomonads can be added to this group of bacteria gifted with secondary metabolites with insecticidal activity. In this study we evaluate several fluorescent pseudomonads with potential biocontrol properties against insects. In a first part we examine the insect toxicity of Pseudomonas cichorii strains NCPPB 907 and SF1-54. We injected the bacteria inside the hemocoel of larvae of greater wax moth (Galleria mellonella) and demonstrate toxicity at concentrations of 106 cfu/larvae. To NCPPB 907, MCP was suggested to play a key role in insect toxicity. Our assays confirm this statement and show reduced mortality of G. mellonella injected with the MCP mutant of NCPPB 907. However, we cannot demonstrate a restoration of the insecticidal activity with the MCP complementary strain. In order to further elucidate the pathogenicity mechanisms we examined several known virulence factors with mutant strains of SF1-54. Although important to some bacteria in their pathogenicity, neither the GacS/GacA two component regulatory system, nor the type III secretory system were of importance in insect toxicity of P. cichorii SF1-54. Nevertheless, the mutant impaired of cichopeptin production caused higher mortality. How the absence of the cichopeptins augment the insecticidal capacity is still up to speculation. Secondly, we evaluate the insecticidal properties of Pseudomonas sp. CMR12a, a very potent biocontrol agent. By injection in the hemocoel of G. mellonella larvae we demonstrated insect toxicity of CMR12a at very low concentrations down to 80 cfu/larvae. FitD, a recently iii characterized insect toxin in Pseudomonas CHA0 and also associated with CMR12a, was confirmed by our study to be present in CMR12a and is most likely to be responsible for its entomopathogenic characteristic. However, residual mortality remained in fitD mutants of CHA0 indicating for additional insecticidal components. Mutants of CMR12a impaired of the production of multiple secondary metabolites did not show any significant differences in mortality against G. mellonella in comparison to the wild type, except for the gacA mutant. The gacA mutant showed a clear increased activity. We suggest this phenomenon to be a result of “growth advantage in stationary phase” (GASP). GASP occurs when spontaneous mutants get a competitive advantage due to the reduced number of expressed metabolites. Results from oral toxicity assays where cottonworm caterpillars (Spodoptera littoralis) were presented with inoculated artificial diet, indicate that CMR12a cannot cause mortality after digestion. A third part consists of the further characterization of novel biocontrol pseudomonads. Insecticidal properties can be used to differentiate strain from each other and to attribute potential control properties. In a virulence assay we demonstrate mortality of G. mellonella larvae injected with NSE1 at 8 x 104 cfu/larva. With this result we deliver proof of NSE1 and NNC8 being different strains, although them being classified as closely related strains. With a DNA sequence analysis we demonstrate the presence of the insect toxin FitD in CMR12a and CMR5c. The sequence analysis of the novel pseudomonad strains did not generate clear results, which indicate that the proposed primers are not specific enough to be applied on all Pseudomonas spp. iv SAMENVATTING Al sinds de eerste beschrijvingen van plant-microbiële interacties in de bodem werden micro-organismen met specifieke gunstige eigenschappen onderzocht om mogelijks te dienen als alternatief voor conventionele gewasbeschermingsmaatregelen, die veelal gebaseerd zijn op het gebruik van synthetische pesticiden. Daaruit vloeide een exponentiële groei aan onderzoek naar het beheersen of bestrijden van bodem gebonden plantpathogenen door middel van micro-organismen. Recent werd ook de bestrijding van insectenplagen met bacteriën meer uitgelicht. Na de prominente ontdekkingen van insecten toxines geproduceerd door Bacillus thuringiensis en door de nematoden-symbiotische Photorhabdus spp en Xenorhabdus spp., kan men nu ook een aantal fluorescente pseudomonaden toevoegen aan de lijst van entomopathogene bacteriën. In deze studie onderzoeken we enkele fluorescente pseudomonaden op hun potentieel vermogen om insectenplagen te bestrijden. In een eerste luik onderzochten we de toxiciteit van Pseudomonas cichorii SF1-54 en NCPPB 907 ten opzichte van insecten. We injecteerden bacteriën in het hemocoel van wasmot larven (Galleria mellonella) en toonden daarbij toxiciteit aan van NCPPB 907 en SF1-54 bij concentraties van 1 x 106 cfu/larve. Voor de stam NCPPB 907 werd gesuggereerd dat de chemotaxis proteïne MCP een cruciale rol zou spelen in de insecten toxiciteit. Onze proeven bevestigen deze veronderstelling vermits een reductie in mortaliteit van G. mellonella geïnjecteerd met MCP-mutanten werd geobserveerd. Wanneer we echter de larven injecteerden met complementaire stammen konden we geen herstel van toxiciteit waarnemen. Met het oog op het verder uitklaren van ziektemechanismen
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