Characterization of the molecular mechanisms controlling negative chemotaxis to copper in Caulobacter crescentus

Abstract

Bacteria have developed various mechanisms to maintain their fitness in an ever-changing environment. They encounter a wide variety of stresses, such as heavy metals. Copper (Cu) is an essential trace element but becomes cytotoxic at higher concentration. We have previously shown that the dimorphic aquatic bacterium Caulobacter crescentus uses a bi-modal strategy to cope with toxic Cu concentrations. The sessile stalked cell triggers Cu oxidation and efflux within minutes while the motile swarmer cell rapidly flees from the Cu source (Lawarée et al., 2016).
The molecular mechanisms underlying bacterial chemotaxis upon heavy metals exposure have remained unknown so far. A high cellular Cu concentration is essential for C. crescentus negative chemotaxis, suggesting that a Cu sensory system monitors intracellular variations of Cu concentration.
A bioinformatics analysis reveals the presence of 19 chemoreceptors (MCPs – Methyl-accepting Chemotaxis Proteins) encoding genes in C. crescentus genome. Their invalidation coupled to the analysis of their Cu chemotactic properties by Live Chemotaxis Imaging (LCI) led us to isolate the Cu chemotaxis-defective ΔmcpR mutant.
In silico analysis of the McpR sensor domain shows a PAS domain potentially involved in O2 and redox sensing, containing a cysteine and several histidines and methionines. These predictions suggest that McpR could sense Cu and/or Cu-generated ROS.
By using the rxYFP biosensor and the DeepRed CellROX, we show that Cu leads to the generation of oxidative stress. In addition, we highlight a link between the Cu-induced ROS and Cu chemotaxis since strains overexpressing SODs and catalase do not trigger Cu chemotaxis.
The involvement of McpR in both H2O2 and Cu chemotaxis suggests a double sensing of Cu and Cu-induced ROS by McpR, sustaining Cu chemotaxis.

Date of Award	2021
Original language	English
Awarding Institution	University of Namur
Sponsors	Fund for Research Training in Industry and Agriculture (FRIA)
Supervisor	Jean-Yves Matroule (Supervisor), Xavier De Bolle (Jury), Emilia Mauriello (Jury), Abram Aertsen (Jury) & Jean-François Collet (Jury)