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

Thesis (MSc)--Stellenbosch University, 2018.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

Bacteria of the genus xenorhabdus, a novel source of bioactive compounds

CITATION: Dreyer, J., Malan, A. P. & Dicks, L. M. T. 2018. Bacteria of the genus xenorhabdus, a novel source of bioactive compounds. Frontiers in Microbiology, 9:3177, doi:10.3389/fmicb.2018.03177.The original publication is available at https://www.frontiersin.orgPublication of this article was funded by the Stellenbosch University Open Access Fund.The genus Xenorhabdus of the family Enterobacteriaceae, are mutualistically associated with entomopathogenic nematodes of the genus Steinernema. Although most of the associations are species-specific, a specific Xenorhabdus sp. may infect more than one Steinernema sp. During the Xenorhabdus–Steinernema life cycle, insect larvae are infected and killed, while both mutualists produce bioactive compounds. These compounds act synergistically to ensure reproduction and proliferation of the nematodes and bacteria. A single strain of Xenorhabdus may produce a variety of antibacterial and antifungal compounds, some of which are also active against insects, nematodes, protozoa, and cancer cells. Antimicrobial compounds produced by Xenorhabdus spp. have not been researched to the same extent as other soil bacteria and they may hold the answer to novel antibacterial and antifungal compounds. This review summarizes the bioactive secondary metabolites produced by Xenorhabdus spp. and their application in disease control. Gene regulation and increasing the production of a few of these antimicrobial compounds are discussed. Aspects limiting future development of these novel bioactive compounds are also pointed out.https://www.frontiersin.org/articles/10.3389/fmicb.2018.03177/fullPublisher's versio