REGULATION OF LACTONASE EXPRESSION IN Serratia marcescens: ROLE OF QUORUM SENSING AND UREA-DEPENDENT INDUCTION

TUTTOBENE, MARISEL ROMINA; ARANGO, BRAYAN; VESCOVI, ELEONORA GARCÍA

Chapadmalal

Congreso; SAMIGE 2023; 2023

SAMIGE

Serratia marcescens is an opportunistic bacterial pathogen that causes a broad-spectrum of infections in humans, in recent years, it has become a public health concern, especially for immunocompromised patients and neonates. Bacteria have evolved a community genetic regulatory mechanism known as “Quorum sensing” (QS), which relies in QS signals such as Acyl-homoserine lactone (AHL) to synchronize the expression of genes involved in pathogenesis, virulence and biofilm production. The disruption of QS signaling through AHL degradation is known as “Quorum Quenching”, enzymes such as lactonases have been identified to cleave the lactone ring of AHL. Understanding how the QS and QQ is regulated remains crucial for designing new therapeutic targets. In our laboratory, we identified an AHL-degrading lactonase in a clinical Serratia marcescens strain, isolated from a urinary tract infection. We found that the lactonase expression is up-regulated when Serratia is exposed to urine or to a urea-containing medium (0,2M to 0,4M concentration range). To identify regulators responsible for lactonase induced expression in the presence of urea, we employed a green fluorescent protein-based reporter plasmid to measure lactonase expression in Serratia marcescens wild-type versus mutant strains deleted in global regulators (rssB, rcsB, phoP, fliA, flhD, ompR, cpxR and luxR). Inhibition of lactonase expression was observed in either ΔcpxR and ΔluxR mutant background strains, even in the presence of urea. In vitro binding of purified CpxR and LuxR proteins to the lactonase gene promoter region was tested by the DNA electromobility shift assay. Results revealed that CpxR directly binds to the lactonase promoter. DNA binding affinity was enhanced by the addition of the alternative CpxR phosphate donor acetyl phosphate. In contrast, no LuxR binding was observed, suggesting an indirect regulation mechanism. In conclusion, results showed a urea-dependent induction of lactonase expression that is modulated by a signal transduction mechanism that relies both on the regulatory activity of both CpxR and LuxR.