hipBA toxin-antitoxin systems mediate persistence in Caulobacter crescentus

Area of Science:

• Microbiology
• Bacterial Physiology
• Molecular Biology

Background:

• Antibiotic persistence is a survival mechanism where bacteria tolerate lethal antibiotic concentrations.
• The HipBA toxin-antitoxin system in Escherichia coli promotes persistence by inhibiting growth via HipA toxin.
• It is unknown if the E. coli HipBA persistence mechanism is conserved in other bacterial species.

Purpose of the Study:

• To investigate the function of three hipBA modules in the alpha-proteobacterium Caulobacter crescentus.
• To determine if the HipBA system in C. crescentus contributes to antibiotic persistence.
• To identify the substrates phosphorylated by C. crescentus HipA toxins.

Main Methods:

• Genetic analysis of Caulobacter crescentus hipBA operons and spoT.
• Biochemical assays to determine HipA kinase activity and substrate specificity.
• Assessment of antibiotic persistence in wild-type and mutant strains.

Main Results:

• Caulobacter crescentus possesses three distinct hipBA modules with HipA toxins exhibiting varied effects on growth and macromolecular synthesis.
• Two HipA toxins, HipA1 and HipA2, phosphorylate aminoacyl-tRNA synthetases GltX and TrpS, respectively, contributing to stationary phase antibiotic persistence.
• While the stringent response regulator SpoT is required for HipA-mediated persistence, persister cell formation can occur independently of hipBA operons or spoT, indicating multiple pathways.

Conclusions:

• The HipBA toxin-antitoxin system contributes to antibiotic persistence in Caulobacter crescentus, but through mechanisms distinct from E. coli.
• Multiple pathways, including but not limited to the HipBA system and SpoT-dependent stringent response, mediate persister cell formation in C. crescentus.
• This study reveals the complexity of antibiotic persistence strategies in bacteria and highlights the potential for novel therapeutic targets.