Efflux and motility are two key biological functions in bacteria. Recent findings have shown that efflux impacts flagellum biosynthesis and motility in
Efflux and motility play a major role in bacterial growth, colonization, and survival. In
Chemical signalling in the plant microbiome can have drastic effects on microbial community structure, and on host growth and development. Previously, we demonstrated that the auxin metabolic signal interference performed by the bacterial genus
- Award ID(s):
- 1917270
- NSF-PAR ID:
- 10376376
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Microbiology
- Volume:
- 7
- Issue:
- 11
- ISSN:
- 2058-5276
- Page Range / eLocation ID:
- p. 1817-1833
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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ABSTRACT Escherichia coli and other bacteria. AcrR is known to be the major transcriptional repressor of AcrAB-TolC, the main multidrug efflux pump inE. coli and otherEnterobacteriaceae . However, the underlying molecular mechanisms of how efflux and motility are co-regulated remain poorly understood. Here, we have studied the role of AcrR in direct regulation of motility inE. coli . By combining bioinformatics, electrophoretic mobility shift assays (EMSAs), gene expression, and motility experiments, we have found that AcrR represses motility inE. coli by directly repressing transcription of theflhDC operon, but not the other flagellum genes/operons tested.flhDC encodes the master regulator of flagellum biosynthesis and motility genes. We found that such regulation primarily occurs by direct binding of AcrR to theflhDC promoter region containing the first of the two predicted AcrR-binding sites identified in this promoter. This is the first report of direct regulation by AcrR of genes unrelated to efflux or detoxification. Moreover, we report that overexpression of AcrR restores to parental levels the increased swimming motility previously observed inE. coli strains without a functional AcrAB-TolC pump, and that such effect by AcrR is prevented by the AcrR ligand and AcrAB-TolC substrate ethidium bromide. Based on these and prior findings, we provide a novel model in which AcrR senses efflux and then co-regulates efflux and motility inE. coli to maintain homeostasis and escape hazards.IMPORTANCE Escherichia coli , the transcriptional repressor AcrR is known to directly repress efflux and was later found to also repress flagellum biosynthesis and motility by Kim et al. (J Microbiol Biotechnol 26:1824–1828, 2016, doi: 10.4014/jmb.1607.07058). However, it remained unknown whether AcrR represses flagellum biosynthesis and motility directly and through which target genes, or indirectly because of altering the amount of efflux. This study reveals that AcrR represses flagellum biosynthesis and motility by directly repressing the expression of theflhDC master regulator of flagellum biosynthesis and motility genes, but not the other flagellum genes tested. We also show that the antimicrobial, efflux pump substrate, and AcrR ligand ethidium bromide regulates motility via AcrR. Overall, these findings support a novel model of direct co-regulation of efflux and motility mediated by AcrR in response to stress inE. coli . -
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Abstract Carboxysomes are protein‐based organelles essential for carbon fixation in cyanobacteria and proteobacteria. Previously, we showed that the cyanobacterial nucleoid is used to equally space out β‐carboxysomes across cell lengths by a two‐component system (McdAB) in the model cyanobacterium
Synechococcus elongatus PCC 7942. More recently, we found that McdAB systems are widespread among β‐cyanobacteria, which possess β‐carboxysomes, but are absent in α‐cyanobacteria, which possess structurally and phyletically distinct α‐carboxysomes. Cyanobacterial α‐carboxysomes are thought to have arisen in proteobacteria and then horizontally transferred into cyanobacteria, which suggests that α‐carboxysomes in proteobacteria may also lack the McdAB system. Here, using the model chemoautotrophic proteobacteriumHalothiobacillus neapolitanus , we show that a McdAB system distinct from that of β‐cyanobacteria operates to position α‐carboxysomes across cell lengths. We further show that this system is widespread among α‐carboxysome‐containing proteobacteria and that cyanobacteria likely inherited an α‐carboxysome operon from a proteobacterium lacking themcdAB locus. These results demonstrate that McdAB is a cross‐phylum two‐component system necessary for positioning both α‐ and β‐carboxysomes. The findings have further implications for understanding the positioning of other protein‐based bacterial organelles involved in diverse metabolic processes.Plain language summary Cyanobacteria are well known to fix atmospheric CO2into sugars using the enzyme Rubisco. Less appreciated are the carbon‐fixing abilities of proteobacteria with diverse metabolisms. Bacterial Rubisco is housed within organelles called carboxysomes that increase enzymatic efficiency. Here we show that proteobacterial carboxysomes are distributed in the cell by two proteins, McdA and McdB. McdA on the nucleoid interacts with McdB on carboxysomes to equidistantly space carboxysomes from one another, ensuring metabolic homeostasis and a proper inheritance of carboxysomes following cell division. This study illuminates how widespread carboxysome positioning systems are among diverse bacteria. Carboxysomes significantly contribute to global carbon fixation; therefore, understanding the spatial organization mechanism shared across the bacterial world is of great interest.
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Summary Auxin is widely involved in plant growth and development. However, the molecular mechanism on how auxin carries out this work is unclear. In particular, the effect of auxin on pre‐
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