Abstract
Antimicrobial multidrug resistance (MDR) is a global challenge, not only for public health, but also for sustainable agriculture. Antibiotics used in humans should be ruled out for use in veterinary or agricultural settings. Applying antimicrobial peptide (AMP) molecules, produced by soil-born organisms for protecting (soil-born) plants, seems a preferable alternative. The natural role of peptide-antimicrobials, produced by the prokaryotic partner of entomopathogenic-nematode/bacterium (EPN/EPB) symbiotic associations, is to sustain monoxenic conditions for the EPB in the gut of the semi-anabiotic infective dauer juvenile (IJ) EPN. They keep pathobiome conditions balanced for the EPN/EPB complex in polyxenic (soil, vanquished insect cadaver) niches. Xenorhabdus szentirmaii DSM16338(T) (EMC), and X. budapestensis DSM16342(T) (EMA), are the respective natural symbionts of EPN species Steinernema rarum and S. bicornutum. We identified and characterized both of these 15 years ago. The functional annotation of the draft genome of EMC revealed 71 genes encoding non-ribosomal peptide synthases, and polyketide synthases. The large spatial Xenorhabdus AMP (fabclavine), was discovered in EMA, and its biosynthetic pathway in EMC. The AMPs produced by EMA and EMC are promising candidates for controlling MDR prokaryotic and eukaryotic pathogens (bacteria, oomycetes, fungi, protozoa). EMC releases large quantity of iodinin (1,6-dihydroxyphenazine 5,10-dioxide) in a water-soluble form into the media, where it condenses to form spectacular water-insoluble, macroscopic crystals. This review evaluates the scientific impact of international research on EMA and EMC.
Highlights
Antimicrobial multidrug-resistance (MDR) [1] is an indirect consequence of large-scale and non-professional applications of previously powerful antibiotics, leading to the situation in which the lifesaving role of antibiotics has gradually become diminished [2]
Since wild type as well as most cultured plants are by definition “soil-born” organisms, the concept of battling MDR plant pathogens with natural antimicrobial peptides (AMPs) produced by other soil-born organisms was taken into consideration
entomopathogenic bacterium (EPB)-released AMP products provide a monoxenic milieu in the gut of the EPN infective juvenile (IJ) for the non-propagating EPB symbiont [6]
Summary
Antimicrobial multidrug-resistance (MDR) [1] is an indirect consequence of large-scale and non-professional applications of previously powerful antibiotics, leading to the situation in which the lifesaving role of antibiotics has gradually become diminished [2]. EPB-released AMP products provide a monoxenic milieu in the gut of the EPN infective juvenile (IJ) for the non-propagating EPB symbiont [6] This keeps the pathobiome conditions optimally balanced [8] for the EPN/EPB symbiotic complex in the polyxenic colonized insect cadaver and soil. Literature from the last 15 years indicates a trend within EPN/EPB research in this antimicrobial direction This conception led us 15 years ago to search for, and find, isolate, identify, characterize, and deposit, two beneficial AMP-producing EPB strains [9] under the respective names Xenorhabdus szentirmaii nov. All EMA and EMC were isolated from the EPN collection in our laboratory at the Department of Genetics, Eötvös University, Budapest, Hungary [12] Stackabrrandt et al, 2021 Another two EPB species were identified and published in a previous article [9]. The co-evolutionary trends of resistance against antimicrobial peptides [32], and those against conventional antibiotics, must be different [31]
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