HipBA toxin-antitoxin systems mediate persistence in Caulobacter crescentus

Céline Henry,Kathleen R. Ryan,Carlos Gonzalez-Lopez,Ivan Mijakovic,Charlie Y. Huang

doi:10.1038/s41598-020-59283-x

Abstract

Antibiotic persistence is a transient phenotypic state during which a bacterium can withstand otherwise lethal antibiotic exposure or environmental stresses. In Escherichia coli, persistence is promoted by the HipBA toxin-antitoxin system. The HipA toxin functions as a serine/threonine kinase that inhibits cell growth, while the HipB antitoxin neutralizes the toxin. E. coli HipA inactivates the glutamyl-tRNA synthetase GltX, which inhibits translation and triggers the highly conserved stringent response. Although hipBA operons are widespread in bacterial genomes, it is unknown if this mechanism is conserved in other species. Here we describe the functions of three hipBA modules in the alpha-proteobacterium Caulobacter crescentus. The HipA toxins have different effects on growth and macromolecular syntheses, and they phosphorylate distinct substrates. HipA1 and HipA2 contribute to antibiotic persistence during stationary phase by phosphorylating the aminoacyl-tRNA synthetases GltX and TrpS. The stringent response regulator SpoT is required for HipA-mediated antibiotic persistence, but persister cells can form in the absence of all hipBA operons or spoT, indicating that multiple pathways lead to persister cell formation in C. crescentus.

Highlights

Antibiotic persistence is a transient phenotypic state during which a bacterium can withstand otherwise lethal antibiotic exposure or environmental stresses
While no bacterium with multiple HipA toxins has been studied, co-activation of distinct TA systems within the same organism has been reported, and we could not discount the possibility of crosstalk between hipBA modules[32,33]
To assess the effect of each HipA toxin without the possibility of crosstalk, we expressed each HipA from a low-copy plasmid in a strain with all three hipBA operons deleted from the chromosome (ΔhipBA1,2,3)

Summary

Introduction

Antibiotic persistence is a transient phenotypic state during which a bacterium can withstand otherwise lethal antibiotic exposure or environmental stresses. In Escherichia coli, persistence is promoted by the HipBA toxin-antitoxin system. The HipA toxin functions as a serine/threonine kinase that inhibits cell growth, while the HipB antitoxin neutralizes the toxin. TA systems can provide stability to mobile genetic elements in bacterial chromosomes, but a growing body of work indicates that TA modules are involved in additional processes including biofilm formation, phage resistance, stress responses, and antibiotic persistence[9,10,11,12,13]. Named for high incidence of persistence, the hipBA module encodes two proteins, the HipB antitoxin and the HipA toxin, which functions as a serine/threonine kinase[20,21,22]. Mutations in hipA are reported to arise in half of E. coli clinical isolates associated with chronic urinary tract infections, indicating a need for further studies to understand how HipA toxins promote antibiotic persistence[24]

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Results

Conclusion