Characterization of novel Xenorhabdus-Steinernema associations and identification of novel antimicrobial compounds produced by Xenorhabdus khoisanae

Dreyer, Jonike (2018-03)

Thesis (MSc)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Xenorhabdus bacteria are closely associated with Steinernema nematodes. This is a species-specific association. Therefore, a specific Steinernema species is associated with a specific Xenorhabdus species. During the Xenorhabdus-Steinernema life cycle the nematodes infect insect larvae and release the bacteria into the hemocoel of the insect by defecation. The bacteria and nematodes produce several exoenzymes and toxins that lead to septicemia, death and bioconversion of the insect. This results in the proliferation of both the nematodes and bacteria. When nutrients are depleted, nematodes take up Xenorhabdus cells and leave the cadaver in search of their next prey. Xenorhabdus produces various broad-spectrum bioactive compounds during their life cycle to create a semi-exclusive environment for the growth of the bacteria and their symbionts. During this study, a molecular approach was used to identify four Xenorhabdus isolates from Steinernema sacchari SB10T, Steinernema jeffreyense J194T, Steinernema nguyeni F2T and Steinernema litchii WS9T as Xenorhabdus khoisanae SB10 and J194, Xenorhabdus bovienii F2 and Xenorhabdus griffiniae WS9, respectively. Steinernema phylogenetics were analyzed and the X. khoisanae-S. sacchari and X. griffiniae-S. litchii associations proved that X. khoisanae and X. griffiniae has the ability to switch between different nematode clades. Antimicrobial compounds produced by X. khoisanae SB10 were purified and analyzed by high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LCMS), respectively. MS spectra and MSe fragmentation profiles revealed novel antimicrobial compounds with mass-to-charge ratios of 671.41 m/z, 259.17 m/z, 434.27 m/z and/or 341.15 m/z. Additionally, this study reports for the first time, the isolation of PAX peptides, xenocoumacins and xenorhabdins from X. khoisanae.

AFRIKAANSE OPSOMMING: Xenorhabdus bakterieë is naby geassosieer met Steinernema nematodes. Hierdie is ‘n spesie-spesifieke assosiasie. Dit wil sê, ʼn spesifieke Steinernema spesie is geassosieer met ʼn spesifieke Xenorhabdus spesie. Tydens die Xenorhabdus-Steinernema lewenssiklus infekteer die nematodes inseklarwes en word die bakterieë in die hemoseel van die insek vrygestel deur middel van ontlasting. Die bakterieë en nematodes produseer verskeie ekso-ensieme en toksiene wat lei tot septisemie, dood en bio-omskakeling van die insek. Dit lei tot die vermeerdering van beide die nematodes en bakterieë. Sodra nutriente uitgeput is, neem nematodes Xenorhabdus selle op en verlaat die kadawer opsoek na hul volgende prooi. Xenorhabdus produseer verskeie breë-spektrum bioaktiewe verbindings tydens hul lewenssiklus om ‘n gedeeltelike eksklusiewe omgewing te skep vir die groei van die bakterieë en hul simbionte. Gedurende hierdie studie was ‘n molekulêre benadering gebruik om vier Xenorhabdus isolate vanaf Steinernema sacchari SB10T, Steinernema jeffreyense J194T, Steinernema nguyeni F2T en Steinernema litchii WS9T te identifiseer as, Xenorhabdus khoisanae SB10 en J194, Xenorhabdus bovienii F2 en Xenorhabdus griffiniae WS9, afsonderlik. Steinernema filogenetika was geanaliseer en die X. khoisanae-S. sacchari en X. griffiniae-S. litchii assosiasies het bewys dat X. khoisanae en X. griffiniae die vermoë het om te wissel tussen nematodes van verskillende klades. Antimikrobiese verbindings geproduseer deur die isolaat, X. khoisanae SB10, was gesuiwer en geanaliseer deur hoëdrukvloeistofchromatografie (HDVC) en vloeistofchromatografie massa-spektrometrie (VCMS), afsonderlik. MS spektra en MSe fragementasie profiele het nuwe antimikrobiese verbindings met massa-tot-lading verhoudings van 671.41 m/z, 259.17 m/z, 434.27 m/z en/of 341.15 m/z onthul. Vêrder rapporteer hierdie studie, vir die eerste keer, dat PAX peptiede, xenokoumasiene en xenorhabdiene geïsoleer was vanaf X. khoisanae.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103354
This item appears in the following collections: