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1. Ecological relevance of flagellar motility in soil bacterial communities

   https://doi.org/10.1093/ismejo/wrae067  

   Ramoneda, Josep; Fan, Kunkun; Lucas, Jane M.; Chu, Haiyan; Bissett, Andrew; Strickland, Michael S.; Fierer, Noah (April 2024, The ISME Journal)

   Abstract Flagellar motility is a key bacterial trait as it allows bacteria to navigate their immediate surroundings. Not all bacteria are capable of flagellar motility, and the distribution of this trait, its ecological associations, and the life history strategies of flagellated taxa remain poorly characterized. We developed and validated a genome-based approach to infer the potential for flagellar motility across 12 bacterial phyla (26 192 unique genomes). The capacity for flagellar motility was associated with a higher prevalence of genes for carbohydrate metabolism and higher maximum potential growth rates, suggesting that flagellar motility is more prevalent in environments with higher carbon availability. To test this hypothesis, we applied a method to infer the prevalence of flagellar motility in whole bacterial communities from metagenomic data and quantified the prevalence of flagellar motility across four independent field studies that each captured putative gradients in soil carbon availability (148 metagenomes). We observed a positive relationship between the prevalence of bacterial flagellar motility and soil carbon availability in all datasets. Since soil carbon availability is often correlated with other factors that could influence the prevalence of flagellar motility, we validated these observations using metagenomic data from a soil incubation experiment where carbon availability was directly manipulated with glucose amendments. This confirmed that the prevalence of bacterial flagellar motility is consistently associated with soil carbon availability over other potential confounding factors. This work highlights the value of combining predictive genomic and metagenomic approaches to expand our understanding of microbial phenotypic traits and reveal their general environmental associations. 

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2. Evolutionary adaptations of doublet microtubules in trypanosomatid parasites

   https://doi.org/10.1126/science.adr5507  

   Doran, Matthew H; Niu, Qingwei; Zeng, Jianwei; Beneke, Tom; Smith, James; Ren, Peter; Fochler, Sophia; Coscia, Adrian; Höög, Johanna L; Meleppattu, Shimi; et al (March 2025, Science)

   The movement and pathogenicity of trypanosomatid species, the causative agents of trypanosomiasis and leishmaniasis, are dependent on a flagellum that contains an axoneme of dynein-bound doublet microtubules (DMTs). In this work, we present cryo–electron microscopy structures of DMTs from two trypanosomatid species,Leishmania tarentolae and Crithidia fasciculata, at resolutions up to 2.7 angstrom. The structures revealed 27 trypanosomatid-specific microtubule inner proteins, a specialized dynein-docking complex, and the presence of paralogous proteins that enable higher-order periodicities or proximal-distal patterning. Leveraging the genetic tractability of trypanosomatid species, we quantified the location and contribution of each structure-identified protein to swimming behavior. Our study shows that proper B-tubule closure is critical for flagellar motility, exemplifying how integrating structural identification with systematic gene deletion can dissect individual protein contributions to flagellar motility. 

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3. The swimming defect caused by the absence of the transcriptional regulator LdtR in Sinorhizobium meliloti is restored by mutations in the motility genes motA and motS

   https://doi.org/10.1111/mmi.15247  

   Sobe, Richard C.; Scharf, Birgit E. (March 2024, Molecular Microbiology)

   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 MotA_G12Salso restored the ΔldtRmotility defect. The MotA_G12Svariant 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/MotA_G12Smight stabilize its interaction with altered peptidoglycan. 

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4. Phages on filaments: A genetic screen elucidates the complex interactions between Salmonella enterica flagellin and bacteriophage Chi

   https://doi.org/10.1371/journal.ppat.1011537  

   Esteves, Nathaniel C; Bigham, Danielle N; Scharf, Birgit E (August 2023, PLOS Pathogens)

   Navarre, William (Ed.)

   The bacterial flagellum is a rotary motor organelle and important virulence factor that propels motile pathogenic bacteria, such asSalmonella enterica, through their surroundings. Bacteriophages, or phages, are viruses that solely infect bacteria. As such, phages have myriad applications in the healthcare field, including phage therapy against antibiotic-resistant bacterial pathogens. Bacteriophage χ (Chi) is a flagellum-dependent (flagellotropic) bacteriophage, which begins its infection cycle by attaching its long tail fiber to theS.entericaflagellar filament as its primary receptor. The interactions between phage and flagellum are poorly understood, as are the reasons that χ only kills certainSalmonellaserotypes while others entirely evade phage infection. In this study, we used molecular cloning, targeted mutagenesis, heterologous flagellin expression, and phage-host interaction assays to determine which domains within the flagellar filament protein flagellin mediate this complex interaction. We identified the antigenic N- and C-terminal D2 domains as essential for phage χ binding, with the hypervariable central D3 domain playing a less crucial role. Here, we report that the primary structure of theSalmonellaflagellin D2 domains is the major determinant of χ adhesion. The phage susceptibility of a strain is directly tied to these domains. We additionally uncovered important information about flagellar function. The central and most variable domain, D3, is not required for motility inS. Typhimurium 14028s, as it can be deleted or its sequence composition can be significantly altered with minimal impacts on motility. Further knowledge about the complex interactions between flagellotropic phage χ and its primary bacterial receptor may allow genetic engineering of its host range for use as targeted antimicrobial therapy against motile pathogens of the χ-host generaSalmonella,Escherichia, orSerratia. 

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5. Photoactivated carbon dots inducing bacterial functional and molecular alterations

   https://doi.org/10.1039/D2MA00403H  

   Dong, Xiuli; Wang, Ping; Rodriguez, Cristian E.; Tang, Yongan; Kathariou, Sophia; Sun, Ya-Ping; Yang, Liju (August 2022, Materials Advances)

   Carbon dots (CDots) of small carbon nanoparticles with oligomeric polyethylenimine for surface functionalization, coupled with visible light exposure, were found highly effective in the inactivation of bacterial pathogens. In this study, using a representative strain of a major foodborne pathogen – Listeria monocytogenes , as a target, the effects of the CDots treatment at sublethal concentrations on bacterial functions/behaviors related to the biofilm formation ability/potential, including cell attachment and swimming motility, were assessed. On the consequence at molecular level, the expression levels of the genes that are related to cell attachment/adhesion, motility, flagellar synthesis, quorum sensing, and environmental stress response and virulence were found all being up-regulated. 

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