Communication Breakdown: Into the Molecular Mechanism of Biofilm Inhibition by CeO₂ Nanocrystal Enzyme Mimics and How It Can Be Exploited

Abstract

Bacterial biofilm formation is a huge problem in industry and medicine. Therefore, the discovery of anti-biofilm agents may hold great promise. Biofilm formation is usually a consequence of bacterial cell–cell communication, a process called quorum sensing (QS). CeO2 nanocrystals (NCs) have been established as haloperoxidase (HPO) mimics and ecologically beneficial biofilm inhibitors. They were suggested to interfere with QS, a mechanism termed quorum quenching (QQ), but their molecular mechanism remained elusive. We show that CeO2 NCs are effective QQ agents, inactivating QS signals by bromination. Catalytic bromination of 3-oxo-C12-AHL a QS signaling compound used by Pseudomonas aeruginosa, was detected in the presence of CeO2 NCs, bromide ions, and hydrogen peroxide. Brominated acyl-homoserine lactones (AHLs) no longer act as QS signals but were not detected in the bacterial cultures. Externally added brominated AHLs also disappeared in P. aeruginosa cultures within minutes of their addition, indicating that they are rapidly degraded by the bacteria. Moreover, we detected the catalytic bromination of 2-heptyl-1-hydroxyquinolin-4­(1H)-one (HQNO), a multifunctional non-AHL QS signal from P. aeruginosa with antibacterial and algicidal properties controlling the expression of many virulence genes. Brominated HQNO was not degraded by the bacteria in vivo. The repression of the Pseudomonas quinolone signal (PQS) production and biofilm formation in P. aeruginosa through the catalytic formation of Br-HQNO on surfaces with coatings containing CeO2 enzyme mimics validates the non-toxic strategy for the development of anti-infectives.

In situ generation of H2O2 using CaO2 as peroxide storage depot for haloperoxidase mimicry with surface-tailored Bi-doped mesoporous CeO2 nanozymes

“…Thus, the bromination of phenol red to tetrabromophenol blue does not proceed. We do not show here again the biofilm inhibiting properties of the PES–BiCe–CaO 2 composites, because this has already been reported before for CeO 2 /paint, 26 Bi 0.2 CeO 1.9 O 1.95 /PES, 36 CeO 2 /polyurethane 54 or CeO 2− x /polycarbonate 61,62 composites.…”

“…Likewise, no oxidative bromination occurred in the absence of H 2 O 2 , i.e., peroxide is essential for the initiation of the reaction. The porous structure of the polymer beads facilitates the diffusion of dissolved ionic or low molecular reactants (i.e., signaling compounds for quorum quenching of bacteria [13][14][15]54 ) through the polymer and ensures that the catalytic haloperoxidase-like reaction always proceeds. So, the idea is similar to that of modern drug delivery systems, where drugs are released from nanoparticles or polymer capsules.…”

Bromination of Quorum Sensing Molecules: Vanadium Bromoperoxidase and Cerium Dioxide Nanocrystals via Free Active Bromine Transform Bacterial Communication

“…TP301 could be confirmed by an in-house synthesized standard (Table S5 of the Supporting Information). Further details were reported by Pütz et al…”

“…However, the influence of cerium dioxide NCs on QSMs is not fully understood. Pütz et al showed that the communication molecules C 4 -AHL and 3-OH-C 10 -AHL were not degraded from cerium dioxide NCs, but the long-chain AHL 3-Oxo-C 12 -AHL and N -Oxo-2-heptyl-4-quinolone (HQNO), a quinolone-like HHQ, can be catalytically brominated and transformation products (TPs) were identified. Michels et al showed the halogenation of short-chain AHL 3-Oxo-C 6 -AHL for active halogen and proposed a transformation pathway.…”

Construction of microbial consortia for microbial degradation of complex compounds

“…QS primarily regulates collective features that involve energetically costly “public goods” and are most effective or even only functional if performed by a microbial consortium. Bacterial traits controlled by QS include genetic phenotypes, biofilm formation, promoting or inhibiting function, and virulence ( Mashruwala et al, 2022 ; Pütz et al, 2022 ; Ramsay et al, 2022 ). QS even can be a driver and target of other functions ( Striednig and Hilbi, 2022 ).…”