Global Transcriptomics and Targeted Metabolite Analysis Reveal the Involvement of the AcrAB Efflux Pump in Physiological Functions by Exporting Signaling Molecules inPhotorhabdus laumondii
Authors: Hadchity Linda , Lanois-Nouri Anne , Chouchou Adrien , Roche David , Houard Jessica , Claveyroles Noémie , Dauvé Alexandra , Imbert Jacques , Gualtieri Maxime , Givaudan Alain , Carré-Mlouka Alyssa , Khattar Ziad Abi 
Published: February 2025

In Gram-negative bacteria, resistance-nodulation-division-type efflux pumps, particularly AcrAB-TolC, play a critical role in mediating resistance to antimicrobial agents and toxic metabolites, contributing to multidrug resistance.Photorhabdus laumondiiis an entomopathogenic bacterium that has garnered significant interest due to its production of bioactive specialized metabolites with anti-inflammatory, antimicrobial, and scavenger deterrents properties. In previous work, we demonstrated that AcrAB confers self-resistance to stilbenes inP. laumondiiTT01. Here, we explore the pleiotropic effects of AcrAB in this bacterium. RNA sequencing of ΔacrAcompared to wild-type revealed growth-phase-specific gene regulation, with stationary-phase cultures showing significant downregulation of genes involved in stilbenes, fatty acid, and anthraquinone pigment biosynthesis, as well as genes related to cellular clumping and fimbrial pilin formation. Genes encoding putative LuxR regulators, type VI secretion systems, two-partner secretion systems, and contact dependent growth inhibition systems were upregulated in ΔacrA. Additionally, exponential-phase cultures revealed reduced expression of genes related to motility in ΔacrA. The observed transcriptional changes were consistent with phenotypic assays, demonstrating that the ΔacrAmutant had altered bioluminescence and defective orange pigmentation due to disrupted anthraquinone production. These findings confirm the role of stilbenes as signaling molecules involved in gene expression, thereby shaping these phenotypes. Furthermore, we showed that AcrAB contributes to swarming and swimming motilities independently of stilbenes. Collectively, these results highlight that disruptingacrABcauses transcriptional and metabolic dysregulation inP. laumondii, likely by impeding the export of key signaling molecules such as stilbenes, which may serve as a ligand for global transcriptional regulators.

Importance

Recent discoveries have highlightedPhotorhabdus laumondiias a promising source of novel anti-infective compounds, including non-ribosomal peptides and polyketides. One key player in the self-resistance of this bacterium to stilbene derivatives is the AcrAB-TolC complex, which is also a well-known contributor to multidrug-resistance. Here, we demonstrate the pleiotropic effects of the AcrAB efflux pump inP. laumondiiTT01, impacting secondary metabolite biosynthesis, motility, and bioluminescence. These effects are evident at transcriptional, metabolic, and phenotypic levels and are likely mediated by the efflux of signaling molecules such as stilbenes. These findings shed light on the multifaceted roles of efflux pumps and open avenues to better explore the complexity of RND pump-mediated signaling pathways in bacteria, thereby aiding combat multidrug resistant infections.