Fabclavine diversity in Xenorhabdus bacteria

Abstract

The global threat of multiresistant pathogens has to be answered by the development of novel antibiotics. Established antibiotic applications are often based on so-called secondary or specialized metabolites (SMs), identified in large screening approaches. To continue this successful strategy, new sources for bioactive compounds are required, such as the bacterial genera Xenorhabdus or Photorhabdus. In these strains, fabclavines are widely distributed SMs with a broad-spectrum bioactivity. Fabclavines are hybrid SMs derived from nonribosomal peptide synthetases (NRPS), polyunsaturated fatty acid (PUFA), and polyketide synthases (PKS). Selected Xenorhabdus and Photorhabdus mutant strains were generated applying a chemically inducible promoter in front of the suggested fabclavine (fcl) biosynthesis gene cluster (BGC), followed by the analysis of the occurring fabclavines. Subsequently, known and unknown derivatives were identified and confirmed by MALDI–MS and MALDI–MS2 experiments in combination with an optimized sample preparation. This led to a total number of 22 novel fabclavine derivatives in eight strains, increasing the overall number of fabclavines to 32. Together with the identification of fabclavines as major antibiotics in several entomopathogenic strains, our work lays the foundation for the rapid fabclavine identification and dereplication as the basis for future work of this widespread and bioactive SM class.

Editorial: New Antimicrobial Peptides From Bacteria/Invertebrate Obligate Symbiotic Associations

“…This Research Topic (RT) was designed as a platform for publications from separate trends in AMP research, focusing on ribosomal templated and non-ribosomal templated (NRP) AMP molecules, respectively. NRP-AMPs are synthesized via multi-enzyme thiol-template mechanisms mediated by two specific enzymes (non-ribosomal peptide synthetases (NRPS) and/or fatty acid synthase (FAS)-related polyketide synthases, PKS) (Fuchs et al, 2014 ; Wenski et al, 2020 ), encoded by biosynthetic gene clusters (BGC) (Wenski et al, 2019 ). In total, 10 of the 16 submitted manuscripts were accepted, of which five are reviews and five are original research papers that appeared in Frontiers Microbiology.…”

Influence of condensation domains on activity and specificity of adenylation domains

“…Consequently, the pronounced conformational changes of the ASub domain observed in silico are less determined by the opposite C-domain, suggesting dynamic detachment. Therefore, the previously described promiscuity at this position in fabclavine biosynthesis (Wenski et al, 2020) does not seem to be the exclusive result of the FclJ_A6 domains activity, but from the extended gatekeeping function of the FclJ_C6 domain that grants additional spatial flexibility mainly in AOI1.…”

“…FclJ, however, bears another advantage necessary to study the impact of an altered C-A interface on the A domain's substrate recognition profilenamely FclJ_A6. While this particular A domain recognises and activates proline in X. budapestensis and X. hominickii, it also activates threonine and valine in X. szentirmaii (Wenski et al, 2020). As the promiscuity of the latter neither can be explained by differences within the respective proteins' primary structure (~89 % similarity) (Tab.…”

Beyond Soil-Dwelling Actinobacteria: Fantastic Antibiotics and Where to Find Them

“…The fact that these molecules seem to be one of the few widely conserved within the Xenorhabuds/Photorhabdus clade and that those strains that do not produce them produce instead another novel family of hydrophobic depsipeptides termed xefoampeptides suggests these molecules must have a relevant role in the biology of these bacteria [119]. Other relevant NRPS-derived molecules in Xenorhabdus are xenorhabdins and xenorxides (Figure 6), both belonging to the category of dithiolopyrrolone antibiotics and with strong antibacterial and cytotoxic activities [140] and recently identified odilorhabdins, broad spectrum antimicrobials with activity against drug-resistant Gram-negative bacteria and with proven efficacy in animal models of infection [141,142]. Interestingly in Photorhabdus, mevalagmapeptides, gameXpeptides and several other metabolites such as the giant pentadecapeptide NRP kolossin were only identified through promoter exchange, placing their gene clusters under the control of the arabinose inducible P BAD /AraC system [120].…”

“…These molecules also exhibit a broad target spectrum all the way from bacteria to eukaryotes, and have been postulated as protection compounds against food competitors of Xenorhabdus [ 149 ]. Activation of the highly conserved xenocoumacin BGCs in diverse Xenorhabdus species via integration of chemically inducible promoters has led to the recent identification of over 20 more members of this family [ 141 ]. Pristinamycins, originally thought to be produced only by Streptomyces , have also been detected in X. nematophyla cultures, after finding its BGC through comparative genomics.…”