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Abstract The flagellar motor is a powerful macromolecular machine used to propel bacteria through various environments. We determined that flagellar motility of the alpha‐proteobacteriumSinorhizobium melilotiis nearly abolished in the absence of the transcriptional regulator LdtR, known to influence peptidoglycan remodeling and stress response. LdtR does not regulate motility gene transcription. Remarkably, the motility defects of the ΔldtRmutant can be restored by secondary mutations in the motility genemotAor a previously uncharacterized gene in the flagellar regulon, which we namedmotS. MotS is not essential forS. melilotimotility and may serve an accessory role in flagellar motor function. Structural modeling predicts that MotS comprised an N‐terminal transmembrane segment, a long‐disordered region, and a conserved β‐sandwich domain. The C terminus of MotS is localized in the periplasm. Genetics based substitution of MotA with MotAG12Salso restored the ΔldtRmotility defect. The MotAG12Svariant protein features a local polarity shift at the periphery of the MotAB stator units. We propose that MotS may be required for optimal alignment of stators in wild‐type flagellar motors but becomes detrimental in cells with altered peptidoglycan. Similarly, the polarity shift in stator units composed of MotB/MotAG12Smight stabilize its interaction with altered peptidoglycan.
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Thermophilic Dehalococcoidia with unusual traits shed light on an unexpected past
Abstract Although the phylum Chloroflexota is ubiquitous, its biology and evolution are poorly understood due to limited cultivability. Here, we isolated two motile, thermophilic bacteria from hot spring sediments belonging to the genus Tepidiforma and class Dehalococcoidia within the phylum Chloroflexota. A combination of cryo-electron tomography, exometabolomics, and cultivation experiments using stable isotopes of carbon revealed three unusual traits: flagellar motility, a peptidoglycan-containing cell envelope, and heterotrophic activity on aromatics and plant-associated compounds. Outside of this genus, flagellar motility has not been observed in Chloroflexota, and peptidoglycan-containing cell envelopes have not been described in Dehalococcoidia. Although these traits are unusual among cultivated Chloroflexota and Dehalococcoidia, ancestral character state reconstructions showed flagellar motility and peptidoglycan-containing cell envelopes were ancestral within the Dehalococcoidia, and subsequently lost prior to a major adaptive radiation of Dehalococcoidia into marine environments. However, despite the predominantly vertical evolutionary histories of flagellar motility and peptidoglycan biosynthesis, the evolution of enzymes for degradation of aromatics and plant-associated compounds was predominantly horizontal and complex. Together, the presence of these unusual traits in Dehalococcoidia and their evolutionary histories raise new questions about the timing and selective forces driving their successful niche expansion into global oceans.
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- Award ID(s):
- 1757316
- PAR ID:
- 10406366
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- The ISME Journal
- Volume:
- 17
- Issue:
- 7
- ISSN:
- 1751-7362
- Format(s):
- Medium: X Size: p. 952-966
- Size(s):
- p. 952-966
- Sponsoring Org:
- National Science Foundation
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