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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 reported here, as suggested by the APE Ec biosynthetic complex. Further research is required to develop these broad-spectrum antimicrobial compounds into drugs that may be used in the fight against microbial infections.    Electronic supplementary material  The online version of this article (10.1186/s12866-019-1503-x) contains supplementary material, which is available to authorized users.

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