Xenorhabdus khoisanae SB10 produces Lys-rich PAX lipopeptides and a Xenocoumacin in its antimicrobial complex

Abstract

Background Xenorhabdus spp. live in close symbiosis with nematodes of the Steinernema genus. Steinernema nematodes infect an insect larva and release their symbionts into the haemocoel of the insect. Once released into the haemocoel, the bacteria produce bioactive compounds to create a semi-exclusive environment by inhibiting the growth of bacteria, yeasts and molds. The antimicrobial compounds thus far identified are xenocoumacins, xenortides, xenorhabdins, indole derivatives, xenoamicins, bicornutin and a number of antimicrobial peptides. The latter may be linear peptides such as the bacteriocins xenocin and xenorhabdicin, rhabdopeptides and cabanillasin, or cyclic, such as PAX lipopeptides, taxlllaids, xenobactin and szentiamide. Thus far, production of antimicrobial compounds have been reported for Xenorhabdus nematophila, Xenorhabdus budapestensis, Xenorhabdus cabanillasii , Xenorhabdus kozodoii , Xenorhabdus szentirmaii , Xenorhabdus doucetiae , Xenorhabdus mauleonii , Xenorhabdus indica and Xenorhabdus bovienii . Here we describe, for the first time, PAX lipopeptides and xenocoumacin 2 produced by Xenorhabdus khoisanae . These compounds were identified using ultraperformance liquid chromatography, linked to high resolution electrospray ionisation mass spectrometry and tandem mass spectrometry. Results Cell-free supernatants of X. khoisanae SB10 were heat stable and active against Bacillus subtilis subsp. subtilis , Escherichia coli and Candida albicans . Five lysine-rich lipopeptides from the PAX group were identified in HPLC fractions, with PAX1’ and PAX7 present in the highest concentrations. Three novel PAX7 peptides with putative enoyl modifications and two linear analogues of PAX1’ were also detected. A small antibiotic compound, yellow in colour and λ max of 314 nm, was recovered from the HPLC fractions and identified as xenocoumacin 2. The PAX lipopeptides and xenocoumacin 2 correlated with the genes and gene clusters in the genome of X. khoisanae SB10. Conclusion With UPLC-MS and MS e analyses of compounds in the antimicrobial complex of X. khoisanae SB10, a number of PAX peptides and a xenocoumacin were identified. The combination of pure PAX1’ peptide with xenocoumacin 2 resulted in high antimicrobial activity. Many of the fractions did, however, contain labile compounds and some fractions were difficult to resolve. It is thus possible that strain SB10 may produce more antimicrobial compounds than repor...

Profiling the Production of Antimicrobial Secondary Metabolites by Xenorhabdus khoisanae J194 Under Different Culturing Conditions

“…Using the MS-MS analysis and predicted sequence from the xenopep putative operon, a working sequence was deduced as Lys-Haa-Pro-Pro-Leu-Gln-Pro-Val (Figure 8D), with Haa an undetermined hydrophobic residue. (Fuchs et al, 2011;Dreyer et al, 2019), and (C) xenoamicins (Zhou et al, 2013 and this study). Refer to Supplementary Figure S6, S7 for more structural analyses details.…”

“…We also found PAX1′, PAX3′ and PAX5 at lower levels in this extract (Figure 6B). The production of the PAX peptides in this Xenorhabdus strain was much lower than that found by Dreyer et al (2019), and we were unable to purify any member of this family further. However, accurate mass analysis and the PAX biosynthetic gene cluster in this strain's genome supported our identification (Table 3).…”

“…Here we report on the activity of X. khoisanae J194 extracts against P. aeruginosa, E. coli, S. aureus, S. epidermidis and L. monocytogenes under different culture conditions. A previous study on X. khoisanae SB10 (Dreyer et al, 2019) also reported activity against Bacillus subtilis subsp. subtilis and Candida albicans.…”

“…A total of 23 antimicrobial compounds produced by Xenorhabdus spp. have been described, of which the majority have bactericidal and fungicidal activity (reviewed by Dreyer et al, 2019). These include xenocoumacins (Park et al, 2009;Reimer et al, 2009), bicornitun (Böszörményi et al, 2009), PAX peptides (Gualtieri et al, 2009;Dreyer et al, 2019), xenorhabdins (McInerney et al, 1991aMcInerney et al, 1991b), xenorxides (Webster et al, 1996) and benzylideneacetone (Ji et al, 2004).…”

“…have been described, of which the majority have bactericidal and fungicidal activity (reviewed by Dreyer et al, 2019). These include xenocoumacins (Park et al, 2009;Reimer et al, 2009), bicornitun (Böszörményi et al, 2009), PAX peptides (Gualtieri et al, 2009;Dreyer et al, 2019), xenorhabdins (McInerney et al, 1991aMcInerney et al, 1991b), xenorxides (Webster et al, 1996) and benzylideneacetone (Ji et al, 2004). A few antimicrobial compounds are also insecticidal and antiparasitic (Ji et al, 2004;Crawford et al, 2011;Crawford et al, 2012;Grundmann et al, 2013;Zhou et al, 2013;Fuchs et al, 2014;Kronenwerth et al, 2014;Proschak et al, 2014;Reimer et al, 2014;Zhao et al, 2018;Hacker et al, 2018).…”