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Updated: May 17, 2025
Imaging InlC Secretion to Investigate Cellular Infection by the Bacterial Pathogen Listeria monocytogenes
Published on: September 19, 2013
ClpP2 proteasomes and SpxA1 determine Listeria monocytogenes tartrolon B hyper-resistance
Tim Engelgeh1, Sabrina Wamp1, Patricia Rothe1
1FG11 Division of Enteropathogenic bacteria and Legionella, Robert Koch Institute, Wernigerode, Germany.
Abstract:
The foodborne bacterium Listeria monocytogenes is transmitted to humans from various environmental sources through consumption of contaminated plant and animal-based food. L. monocytogenes uses ATP-binding cassette (ABC)-type drug transporters to resist antimicrobial compounds produced by competitors co-residing in its environmental reservoirs. We have shown previously that the TimAB transporter confers resistance of L. monocytogenes to tartrolon B, a boron containing macrodiolide produced by myxo- and proteobacterial species. Tartrolon B acts as a potassium ionophore and is sensed by TimR, the transcriptional repressor of timABR operon. We here have isolated tartrolon B resistant suppressor mutations outside the timABR locus. These mutations inactivated the clpP2 gene, which encodes the main proteolytic component of house-keeping Clp proteases. Deletion of clpP2 impaired growth and virulence but caused tartrolon B hyper-resistance. This phenotype was timAB-dependent, but neither production nor degradation of TimAB was affected upon clpP2 inactivation. Combinatorial deletions of the genes encoding the three Clp ATPases showed that ClpCP2 and ClpXP2 proteasomes jointly promote tartrolon B hyper-resistance. Genetic follow-up experiments identified the ClpP2 substrate and transcription factor SpxA1 and its protease adaptor YjbH as further tartrolon B resistance determinants. SpxA1 activates transcription of the cydABCD operon encoding cytochrome oxidase and in accordance with this transposon mutants with impaired cytochrome oxidase function were depleted from a transposon mutant library during tartrolon B exposure. Our work demonstrates novel roles of Clp proteasomes, SpxA1 and cytochrome oxidase CydAB in the resistance against compounds dissipating transmembrane ion gradients and helps to better understand the genetic and chemical basis of the manifold ecological interactions of an important human pathogen in its natural ecologic niches.
Insights
Listeria monocytogenes resistance to tartrolon B involves Clp proteases, SpxA1, and cytochrome oxidase. These factors help the bacterium survive environmental antimicrobial compounds.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- Listeria monocytogenes is a foodborne pathogen that utilizes ATP-binding cassette (ABC)-type drug transporters for antimicrobial resistance.
- The TimAB transporter confers resistance to tartrolon B, a potassium ionophore produced by bacterial competitors.
- Tartrolon B resistance is regulated by TimR, the transcriptional repressor of the timABR operon.
Purpose of the Study:
- To identify novel genetic determinants of tartrolon B resistance in Listeria monocytogenes.
- To elucidate the roles of Clp proteases and associated factors in bacterial survival against ionophores.
Main Methods:
- Isolation and characterization of tartrolon B resistant suppressor mutations.
- Genetic analysis including gene deletions and combinatorial studies of Clp ATPases.
- Identification of ClpP2 substrates and their role in resistance pathways.
- Transposon sequencing to assess fitness during antimicrobial exposure.
Main Results:
- Suppressor mutations conferring tartrolon B resistance were found in the clpP2 gene, encoding a Clp protease component.
- Deletion of clpP2 impaired bacterial growth and virulence but conferred tartrolon B hyper-resistance.
- ClpCP2 and ClpXP2 proteasomes were found to jointly promote tartrolon B resistance.
- The transcription factor SpxA1 and its adaptor YjbH were identified as key resistance determinants.
- SpxA1 regulates the cydABCD operon, essential for cytochrome oxidase function, which is crucial for resistance.
Conclusions:
- Clp proteasomes, SpxA1, and cytochrome oxidase CydAB play significant roles in Listeria monocytogenes resistance to ionophores.
- These findings reveal new mechanisms of bacterial adaptation to environmental antimicrobial compounds.
- Understanding these resistance pathways enhances knowledge of pathogen interactions in ecological niches.
