Indole-Induced Reversion of Intrinsic Multiantibiotic Resistance in Lysobacter enzymogenes

Abstract

species are a group of environmental bacteria that are emerging as a new source of antibiotics. One characteristic of is intrinsic resistance to multiple antibiotics, which had not been studied. To understand the resistance mechanism, we tested the effect of blocking two-component regulatory systems (TCSs) on the antibiotic resistance of, a prolific producer of antibiotics. Upon treatment with LED209, an inhibitor of the widespread TCS QseC/QseB, produced a large amount of an unknown metabolite that was barely detectable in the untreated culture. Subsequent structural elucidation by nuclear magnetic resonance (NMR) unexpectedly revealed that the metabolite was indole. Indole production was also markedly induced by adrenaline, a known modulator of QseC/QseB. Next, we identified two TCS genes, () and , in and found that mutations of and also led to a dramatic increase in indole production. We then chemically synthesized a fluorescent indole probe that could label the cells. While the (cytoplasmic response regulator) mutant was clearly labeled by the probe, the (membrane sensor) mutant was not labeled. It was reported previously that indole can enhance antibiotic resistance in bacteria. Therefore, we tested if the dramatic increase in the level of indole production in upon blocking of and would lead to enhanced antibiotic resistance. Surprisingly, we found that indole caused the intrinsically multiantibiotic-resistant bacterium to become susceptible. Point mutations at conserved amino acids in -QseC also led to antibiotic susceptibility. Because indole is known as an interspecies signal, these findings may have implications. The environmental bacterium is a new source of antibiotic compounds and exhibits intrinsic antibiotic resistance. Here, we found that the inactivation of a two-component regulatory system (TCS) by an inhibitor or by gene deletion led to a remarkable increase in the level of production of a metabolite in, and this metabolite was identified to be indole. We chemically synthesized a fluorescent indole probe and found that it could label the wild type and a mutant of the TCS cytoplasmic response regulator but not a mutant of the TCS membrane sensor. Indole treatment caused the intrinsically multidrug-resistant bacterium to be susceptible to antibiotics. Mutations of the TCS sensor also led to antibiotic susceptibility. Because indole is known as an interspecies signal between gut microbiota and mammalian hosts, the observation that indole could render intrinsically resistant susceptible to common antibiotics may have implications.

Local and Universal Action: The Paradoxes of Indole Signalling in Bacteria

“…However, two studies reported that indole decreases antibiotic resistance in the Gramnegative Lysobacter species by stimulating the vitamin B12 importer BtuD [37,38]. The weak selectivity of the importer causes cells to increase antibiotic uptake, resulting in cell death [38].…”

Interspecies and Intraspecies Signals Synergistically Regulate Lysobacter enzymogenes Twitching Motility

“…A recently study of ours reported that indole is able to reverse the intrinsic antibiotic resistance of Lysobacter through the two-component regulatory system QseC/QseB. Site-specific mutations in the qseC gene also resulted in antibiotic susceptibility (36). Besides, this antibiotic resistance reversal was facilitated by a novel BtuD-associated importer which can transfer both vitamin B12 and antibiotics (37).…”

Indole Reverses Intrinsic Antibiotic Resistance by Activating a Novel Dual-Function Importer

“…Extraction of plasmids and DNA fragments was performed following the instructions included with the kits purchased from Omega (plasmid mini kit I and gel extraction kit, Omega USA). All molecular manipulations were carried out according to methods described previously (30, 36). Restriction enzymes and molecular biology reagents were purchased from TaKaRa (TaKaRa Bio Group, Japan).…”

“…Another salient feature of Lysobacter spp. is their intrinsic resistance to multiple antibiotics (30). However, the molecular mechanism underlying this intrinsic antibiotic resistance is not well understood, possibly because Lysobacter spp.…”