Browsing by Author "Dreyer, Jonike"
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- ItemBacteria of the genus xenorhabdus, a novel source of bioactive compounds(Frontiers Media, 2018-12-19) Dreyer, Jonike; Malan, Antoinette P.; Dicks, Leon Milner Theodore, 1961-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.
- ItemCharacterization of novel Xenorhabdus-Steinernema associations and identification of novel antimicrobial compounds produced by Xenorhabdus khoisanae(Stellenbosch : Stellenbosch University, 2018-03) Dreyer, Jonike; Dicks, Leon Milner Theodore; Malan, Antoinette P.; Stellenbosch University. Faculty of Science. Dept. of Microbiology.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.