Virtual surgical planning and use of a 3D-printed, patient-specific reduction system for minimally invasive plate osteosynthesis of diaphyseal tibial fractures in dogs: A historic case control study.

OBJECTIVE: To compare the efficacy and clinical outcomes of computed tomography (CT)-based virtual surgical planning (VSP) and a three-dimensional (3D)-printed, patient-specific reduction system to conventional indirect reduction techniques for diaphyseal tibial fractures stabilized using minimally invasive plate osteosynthesis (MIPO) in dogs. STUDY DESIGN: A prospective clinical study with a historic control cohort. SAMPLE POPULATION: Dogs undergoing MIPO stabilization of diaphyseal tibial fractures using a custom 3D-printed reduction system (3D-MIPO; n = 15) or conventional indirect reduction techniques (c-MIPO; n = 14). METHODS: Dogs were prospectively enrolled to the 3D-MIPO group and CT scans were used to design and fabricate a custom 3D-printed reduction system to facilitate MIPO. Medical records were searched to identify dogs for the c-MIPO group. Pre-, intra- and postoperative parameters were compared between groups. RESULTS: The duration from presentation until surgery was 23 h longer in the 3D-MIPO group (p = .002). Fewer intraoperative fluoroscopic images were acquired (p < .001) and mean surgical duration was 34 min shorter in the 3D-MIPO group (p = .014). Median postoperative tibial length, frontal alignment, and sagittal alignment were within 4 mm, 3° and 3°, respectively, of the contralateral tibia in both groups and did not differ between reduction groups (p > .1). Postoperative complications occurred in 27% and 14% of fractures in the 3D-MIPO and c-MIPO groups, respectively. CONCLUSION: Both reduction methods yielded comparable results. Although the preoperative planning and guide preparation was time consuming, surgery times were shorter and fluoroscopy use was less in the 3D-MIPO group. CLINICAL SIGNIFICANCE: VSP and the custom 3D-printed reduction system facilitated efficient MIPO.

Large attachment organelle mediates interaction between Nanobdellota archaeon YN1 and its host.

DPANN archaea are an enigmatic superphylum that are difficult to isolate and culture in the laboratory due to their specific culture conditions and apparent ectosymbiotic lifestyle. Here we successfully isolated and cultivated a co-culture system of a novel Nanobdellota archaeon YN1 and its host Sulfurisphaera ohwakuensis YN1HA. We characterised the co-culture system by complementary methods, including metagenomics and metabolic pathway analysis, fluorescence microscopy, and high-resolution electron cryo-tomography (cryoET). We show that YN1 is deficient in essential metabolic processes and requires host resources to proliferate. CryoET imaging revealed an enormous attachment organelle present in the YN1 envelope that forms a direct interaction with the host cytoplasm, bridging the two cells. Together our results unravel the molecular and structural basis of ectosymbiotic relationship between YN1 and YNHA. This research broadens our understanding of DPANN biology and the versatile nature of their ectosymbiotic relationships.

Label-free, non-contact determination of resting membrane potential using dielectrophoresis.

Measurement of cellular resting membrane potential (RMP) is important in understanding ion channels and their role in regulation of cell function across a wide range of cell types. However, methods available for the measurement of RMP (including patch clamp, microelectrodes, and potential-sensitive fluorophores) are expensive, slow, open to operator bias, and often result in cell destruction. We present non-contact, label-free membrane potential estimation which uses dielectrophoresis to determine the cytoplasm conductivity slope as a function of medium conductivity. By comparing this to patch clamp data available in the literature, we have demonstratet the accuracy of this approach using seven different cell types, including primary suspension cells (red blood cells, platelets), cultured suspension cells (THP-1), primary adherent cells (chondrocytes, human umbilical mesenchymal stem cells), and adherent (HeLa) and suspension (Jurkat) cancer cell lines. Analysis of the effect of ion channel inhibitors suggests the effects of pharmaceutical agents (TEA on HeLa; DMSO and neuraminidase on red blood cells) can also be measured. Comparison with published values of membrane potential suggest that the differences between our estimates and values recorded by patch clamp are accurate to within published margins of error. The method is low-cost, non-destructive, operator-independent and label-free, and has previously been shown to allow cells to be recovered after measurement.

Demand for low-quality offsets by major companies undermines climate integrity of the voluntary carbon market.

Most companies include carbon offsets in their net-zero strategy. However, many offset projects are poor quality and fail to reduce emissions as claimed. Here we focus on the twenty companies retiring the most offsets from the voluntary carbon market over 2020-2023. We examine if their offsets could be considered high quality and likely to benefit the climate. We curate an original company-level dataset to examine quality and climate benefits across four dimensions: (1) use of offsets from low/high-risk project types; (2) age of projects and credits; (3) price of credits; and (4) country of implementation. We find that companies have predominantly sourced low-quality, cheap offsets: 87% carry a high risk of not providing real and additional emissions reductions, with most offsets originating from forest conservation and renewable energy projects. Further, most offsets do not meet industry standards regarding age and country of implementation. These findings provide further evidence that the voluntary carbon market is not supporting effective climate mitigation. Particularly, we show that its persisting quality issues are exacerbated by the demand for low-quality offsets by individual companies.

Neural pathways associated with reduced rigidity during pallidal deep brain stimulation for Parkinson's disease.

Deep brain stimulation (DBS) of the internal segment of the globus pallidus (GPi) can markedly reduce muscle rigidity in people with Parkinson's disease (PD); however, the mechanisms mediating this effect are poorly understood. Computational modeling of DBS provides a method to estimate the relative contributions of neural pathway activations to changes in outcomes. In this study, we generated patient-specific biophysical models of GPi DBS (derived from individual 7T MRI) - including pallidal efferent, putamenal efferent and internal capsule pathways - to investigate how activation of neural pathways contributed to changes in forearm rigidity in PD. Ten individuals (17 arms) were tested off medication under four conditions: off stimulation, on clinically optimized stimulation, and on stimulation specifically targeting the dorsal GPi or ventral GPi. Quantitative measures of forearm rigidity, with and without a contralateral activation maneuver, were obtained using a robotic manipulandum. Clinically optimized GPi DBS settings significantly reduced forearm rigidity (p < 0.001), which aligned with GPi efferent fiber activation. The model demonstrated that GPi efferent axons could be activated at any location along the GPi dorsal-ventral axis. These results provide evidence that rigidity reduction produced by GPi DBS is mediated by preferential activation of GPi efferents to the thalamus, likely leading to a reduction in excitability of the muscle stretch reflex via overdriving pallidofugal output.

A detox dilemma beyond benzodiazepines; clonidine's quandary in alcohol withdrawal management.

BACKGROUND AND OBJECTIVES: Benzodiazepines are the primary method of treatment of alcohol withdrawal, though the American Society of Addiction Medicine guidelines also include alternative agents for consideration. Observations in a Department of Veterans Affairs (VA) psychiatric emergency room noted consistent benzodiazepine use with an overall lack of use of alternative agents, even with low Clinical Institute Withdrawal Assessment for Alcohol (CIWA) scores and in the absence of other concerning symptoms. Due to concerns of potential more-than-necessary benzodiazepine use, we analyzed adjunctive clonidine use for elevated blood pressure/pulse in alcohol withdrawal among this Veteran population. METHODS: This is a single-site VA retrospective chart review of the psychiatric emergency room from July 1, 2022, to June 30, 2023, focused on patients with alcohol withdrawal managed on a CIWA protocol. Excluding concurrent opioid withdrawal and clonidine as home medication, 167 patient charts were analyzed for this study. RESULTS: Among 167 patients, 99 (59.3%) had comorbid hypertension. A total of 614 medication doses were given for elevated CIWA (373, 60.8%) and elevated blood pressure/pulse (241, 39.2%). Of the 241 doses for elevated blood pressure/pulse, only 2.5% were clonidine. Among all benzodiazepine doses, 75.3% were given to patients with comorbid hypertension. Clonidine was administered to 3.0% of patients, making up 2.5% of total dosing. DISCUSSION AND CONCLUSIONS: Alcohol withdrawal management lacks optimization. Integrating adjunctive medications could reduce potential benzodiazepine overuse effectively addressing elevated blood pressure/pulse. SCIENTIFIC SIGNIFICANCE: This study sheds light on the potential underutilization of clonidine and its potential role in improving alcohol withdrawal syndrome management. By addressing elevated blood pressure/pulse and curbing potential overuse of benzodiazepines, it may contribute to further optimizing patient care.

Spanish-Language Measures of Intimate Partner Violence: A Systematic Review of Psychometric Evidence and Translation Methodology.

Intimate partner violence (IPV) is prevalent worldwide, including in Latinx populations. Reported rates of IPV in Latinx populations vary widely, indicating that measurement errors may be impeding researchers' and clinicians' understanding of IPV in these populations. We conducted a systematic review across a range of social science databases to evaluate psychometric properties and translation methodologies of Spanish-language IPV measures. Records were included if they included Spanish measures assessing IPV victimization. We identified 91 records with a total of 70 measures and evaluated the measures' extant psychometric evidence using the COnsensus-based Standards for the selection of health Measurement Instruments. For the measures translated from English to Spanish, we evaluated the translation methodology based on best-practice recommendations for achieving translations that are psychometrically equivalent to their original versions. We found that validation information about measures was sparse and that few translations adhered to best-practice recommendations. Based on our a priori criteria we recommend the Plazaola-Castaño translation of the Index of Spouse Abuse. In closing, we discuss the validity evidence of translated measures independent of the original language version and best-practice recommendations in translating psychological measures.

Prospective Health Impacts of a Universal Basic Income: Evidence from Community Engagement in South Tyneside, United Kingdom.

Studies have suggested that universal basic income (UBI) has the capacity to have substantial health benefits across the population at national level. Multiple impact pathways have recently been theorized and there are calls for trials to explore these pathways empirically. However, very limited research has taken place at local levels to explore potential context-specific effects, or how these effects could play out in economic, social, and behavioral changes. In order to examine these effects and to think through potential issues and unintended consequences, we brought together citizen engagement groups in Jarrow, South Tyneside, in the northeast of England to explore local people's expectations and positions on the development of UBI policies and pilots prior to their implementation. We found that people's expectations regarding the potential beneficial health impacts of UBI on their communities mapped strongly onto academically theorized impact pathways. They also extended understanding of these pathways in meaningful ways. Our findings add to the literature about UBI and health and provide important insights for the future development of empirical, health focused, UBI research.

Genomic incongruence accompanies the evolution of flower symmetry in Eudicots: a case study in the poppy family (Papaveraceae, Ranunculales).

Reconstructing evolutionary trajectories and transitions that have shaped floral diversity relies heavily on the phylogenetic framework on which traits are modelled. In this study, we focus on the angiosperm order Ranunculales, sister to all other eudicots, to unravel higher-level relationships, especially those tied to evolutionary transitions in flower symmetry within the family Papaveraceae. This family presents an astonishing array of floral diversity, with actinomorphic, disymmetric (two perpendicular symmetry axes), and zygomorphic flowers. We generated nuclear and plastid datasets using the Angiosperms353 universal probe set for target capture sequencing (of 353 single-copy nuclear ortholog genes), together with publicly available transcriptome and plastome data mined from open-access online repositories. We relied on the fossil record of the order Ranunculales to date our phylogenies and to establish a timeline of events. Our phylogenomic workflow shows that nuclear-plastid incongruence accompanies topological uncertainties in Ranunculales. A cocktail of incomplete lineage sorting, post-hybridization introgression, and extinction following rapid speciation most likely explain the observed knots in the topology. These knots coincide with major floral symmetry transitions and thus obscure the order of evolutionary events.

The DNA Replication Checkpoint Targets the Kinetochore for Relocation of Collapsed Forks to the Nuclear Periphery.

Hairpin forming expanded CAG/CTG repeats pose significant challenges to DNA replication which can lead to replication fork collapse. Long CAG/CTG repeat tracts relocate to the nuclear pore complex to maintain their integrity. Forks impeded by DNA structures are known to activate the DNA damage checkpoint, thus we asked whether checkpoint proteins play a role in relocation of collapsed forks to the nuclear periphery in S. cerevisiae . We show that relocation of a (CAG/CTG) 130 tract is dependent on activation of the Mrc1/Rad53 replication checkpoint. Further, checkpoint-mediated phosphorylation of the kinetochore protein Cep3 is required for relocation, implicating detachment of the centromere from the spindle pole body. Activation of this pathway leads to DNA damage-induced microtubule recruitment to the repeat. These data suggest a role for the DNA replication checkpoint in facilitating movement of collapsed replication forks to the nuclear periphery by centromere release and microtubule-directed motion. Highlights: The DNA replication checkpoint initiates relocation of a structure-forming CAG repeat tract to the nuclear pore complex (NPC)The importance of Mrc1 (hClaspin) implicates fork uncoupling as the initial checkpoint signalPhosphorylation of the Cep3 kinetochore protein by Dun1 kinase allows for centromere release, which is critical for collapsed fork repositioningDamage-inducible nuclear microtubules (DIMs) colocalize with the repeat locus and are required for relocation to the NPCEstablishes a new role for the DNA replication and DNA damage checkpoint response to trigger repositioning of collapsed forks within the nucleus.

Genome-Wide Profiling of Cis-regulatory Elements in Mammalian Skin.

The modulation of cis-regulatory elements (e.g., enhancers and promoters) is a major mechanism by which gene expression can be controlled in a temporal and spatially restricted manner. However, methods for both identifying these elements and inferring their activity are limited and often require a substantial investment of time, money, and resources. Here, using mammalian skin as a model, we demonstrate a streamlined protocol by which these hurdles can be overcome using a novel chromatin profiling technique (CUT&RUN) to map histone modifications genome-wide. This protocol can be used to map the location and activity of putative cis-regulatory elements, providing mechanistic insight into how differential gene expression is controlled in mammalian tissues.

A reproducible pipeline for parcellation of the anterior limb of the internal capsule.

BACKGROUND: The anterior limb of the internal capsule (ALIC) is a white matter structure connecting the prefrontal cortex (PFC) to the brainstem, thalamus, and subthalamic nucleus. It is a target for deep brain stimulation (DBS) for obsessive-compulsive disorder. There is strong interest in improving DBS targeting by using diffusion tractography to reconstruct and target specific ALIC fiber pathways, but this methodology is susceptible to errors and lacks validation. To address these limitations, we developed a novel diffusion tractography pipeline that generates reliable and biologically validated ALIC white matter reconstructions. METHODS: Following algorithm development and refinement, we analyzed 43 control subjects each with 2 sets of 3T MRI data and a subset of 5 controls with 7T data from the Human Connectome Project. We generated 22 segmented ALIC fiber bundles (11 per hemisphere) based on prefrontal PFC regions of interest, and we analyzed the relationships among bundles. RESULTS: We successfully reproduced the topographies established by prior anatomical work using images acquired at both 3T and 7T. Quantitative assessment demonstrated significantly smaller intra-subject variability relative to inter-subject variability for both test and retest groups across all but one PFC region. We examined the overlap between fibers from different PFC regions and a response tract for obsessive-compulsive disorder deep brain stimulation, and we reconstructed the PFC hyperdirect pathway using a modified version of our pipeline. DISCUSSION: Our dMRI algorithm reliably generates biologically validated ALIC white matter reconstructions, allowing for more precise modelling of fibers for neuromodulation therapies.

Single-Molecule Detection of the Encounter and Productive Electron Transfer Complexes of a Photosynthetic Reaction Center.

Small, diffusible redox proteins play an essential role in electron transfer (ET) in respiration and photosynthesis, sustaining life on Earth by shuttling electrons between membrane-bound complexes via finely tuned and reversible interactions. Ensemble kinetic studies show transient ET complexes form in two distinct stages: an "encounter" complex largely mediated by electrostatic interactions, which subsequently, through subtle reorganization of the binding interface, forms a "productive" ET complex stabilized by additional hydrophobic interactions around the redox-active cofactors. Here, using single-molecule force spectroscopy (SMFS) we dissected the transient ET complexes formed between the photosynthetic reaction center-light harvesting complex 1 (RC-LH1) of Rhodobacter sphaeroides and its native electron donor cytochrome c2 (cyt c2). Importantly, SMFS resolves the distribution of interaction forces into low (∼150 pN) and high (∼330 pN) components, with the former more susceptible to salt concentration and to alteration of key charged residues on the RC. Thus, the low force component is suggested to reflect the contribution of electrostatic interactions in forming the initial encounter complex, whereas the high force component reflects the additional stabilization provided by hydrophobic interactions to the productive ET complex. Employing molecular dynamics simulations, we resolve five intermediate states that comprise the encounter, productive ET and leaving complexes, predicting a weak interaction between cyt c2 and the LH1 ring near the RC-L subunit that could lie along the exit path for oxidized cyt c2. The multimodal nature of the interactions of ET complexes captured here may have wider implications for ET in all domains of life.

Strand asymmetry in the repair of replication dependent double-strand breaks.

Single-strand breaks (SSBs) are one of the most common endogenous lesions and have the potential to give rise to cytotoxic double-strand breaks (DSBs) during DNA replication. To investigate the mechanism of replication fork collapse at SSBs and subsequent repair, we employed Cas9 nickase (nCas9) to generate site and strand-specific nicks in the budding yeast genome. We show that nCas9-induced nicks are converted to mostly double-ended DSBs during S-phase. We find that repair of replication-dependent DSBs requires homologous recombination (HR) and is independent of canonical non-homologous end joining. Consistent with a strong bias to repair these lesions using a sister chromatid template, we observe minimal induction of inter-chromosomal HR by nCas9. Using nCas9 and a gRNA to nick either the leading or lagging strand template, we carried out a genome-wide screen to identify factors necessary for the repair of replication-dependent DSBs. All the core HR genes were recovered in the screen with both gRNAs, but we recovered components of the replication-coupled nucleosome assembly (RCNA) pathway with only the gRNA targeting the leading strand template. By use of additional gRNAs, we find that the RCNA pathway is especially important to repair a leading strand fork collapse.

Congenital hyperinsulinism and novel KDM6A duplications -resolving pathogenicity with genome and epigenetic analyses.

CONTEXT: Hyperinsulinemic hypoglycemia (HI) can be the presenting feature of Kabuki syndrome (KS), which is caused by loss-of-function variants in KMT2D or KDM6A. As these genes play a critical role in maintaining methylation status in chromatin, individuals with pathogenic variants have a disease-specific epigenomic profile -an episignature. OBJECTIVE: We evaluated the pathogenicity of three novel partial KDM6A duplications identified in three individuals presenting with neonatal-onset HI without typical features of KS at the time of genetic testing. METHODS: Three different partial KDM6A duplications were identified by routine targeted next generation sequencing for HI and initially classified as variants of uncertain significance (VUS) as their location, and hence their impact on the gene, was not known. Whole genome sequencing (WGS) was undertaken to map the breakpoints of the duplications with DNA methylation profiling performed in two individuals to investigate the presence of a KS-specific episignature. RESULTS: WGS confirmed the duplication in proband 1 as pathogenic as it caused a frameshift in the normal copy of the gene leading to a premature termination codon. The duplications identified in probands 2 and 3 did not alter the reading frame and therefore their significance remained uncertain after WGS. Subsequent DNA methylation profiling identified a KS-specific episignature in proband 2 but not in proband 3. CONCLUSIONS: Our findings confirm a role for KDM6A partial gene duplications in the etiology of KS and highlight the importance of performing in-depth molecular genetic analysis to properly assess the clinical significance of VUS's in the KDM6A gene.

Tournament Recovery Profiles and Physical Demands in a Collegiate Women's Tennis Team.

ABSTRACT: Tendero-Ortiz, E, Johnson, MJ, Horsfall, CM, Vondrasek, JD, Grosicki, GJ, Riemann, BL, and Flatt, AA. Tournament recovery profiles and physical demands in a collegiate women's tennis team. J Strength Cond Res XX(X): 000-000, 2024-We aimed to characterize recovery profiles and tournament physical demands in women's collegiate tennis players. A Division 1 team (n = 9) participated in the study. Markers of cardiac autonomic (resting heart rate [HR], HR variability), neuromuscular (isometric handgrip strength, seated single-arm shot-put test [SSAPT], hexagon agility, countermovement jump characteristics), and perceptual recovery were obtained before the tournament (baseline) and again 1 and 2 days posttournament. Cardiorespiratory (HR) and movement characteristics from matches were quantified with wearable devices. p values < 0.05 were statistically significant. No recovery markers differed from baseline (ps > 0.05), although small effect size reductions 1 day posttournament were noted for SSAPT, hexagon agility, and select countermovement jump characteristics. In addition, hexagon agility times and SSAPT were slower (p < 0.01) and shorter (p < 0.05), respectively, at 1 versus 2 days posttournament. Similarly, relative to 1 day posttournament, perceptual makers were improved 2 days posttournament (ps < 0.05). Mean and peak HR were higher for singles versus doubles matches  (ps < 0.05). Except for average speed, movement parameters were greater during singles versus doubles matches (ps < 0.05). Markers of recovery were minimally affected 1 day posttournament relative to baseline, but perceptual and select neuromuscular markers were most improved 2 days posttournament. Thus, passive rest or limited intensity training 1 day posttournament seems advisable. Competition HR and movement profiles inform practitioners of the cardiorespiratory and locomotor demands of women's collegiate tennis, which may be useful in designing preparatory conditioning programs to ensure that players attain match-specific physical capacities in training before competition.

Species-specific bioassays reveal spatial variation in chemical contamination of green sea turtles.

The rapid increase of anthropogenic activity at shipping ports and surrounding coastal areas has been correlated with higher chemical contamination entering the surrounding marine environment. Chemical contaminants in marine environments can lead to significant health problems for green turtles (Chelonia mydas), especially when these contaminants accumulate in their foraging grounds. This study examined the exposure and toxicological effects of chemical contaminants on green turtle cells using a species-specific cell viability assay. Using the QuEChERs extraction, organic contaminants were extracted from 60 blood samples collected from green turtles in three foraging locations: Port Curtis, and two reefs (Heron Reef and Hoskyn-Fairfax Reefs) within the Capricorn Bunker Group of the outer Great Barrier Reef. Blood extracts were tested for cytotoxicity against primary green turtle fibroblast cells using an in vitro resazurin bioassay to assess cell viability. Extracts from Gladstone and Heron Reef indicated significant chemical contamination, at levels high enough to cause adverse health effects of green turtles. Very low toxicity values at the Hoskyn-Fairfax Reefs location indicate its potential to be established as a reference site for the southern Great Barrier Reef.

Trace metal accumulation through the environment and wildlife at two derelict lead mines in Wales.

Trace metal pollution is globally widespread, largely resulting from human activities. Due to the persistence and high toxicity of trace metals, these pollutants can have serious effects across ecosystems. However, few studies have directly assessed the presence and impact of trace metal pollution across ecosystems, specifically across multiple environmental sources and animal taxa. This study was designed to assess the environmental health impacts of trace metal pollution by assessing its extent and possible transfer into wildlife in the areas surrounding two abandoned metalliferous mine complexes in Wales in the UK. Water, sediment, and soil at the mine sites and in areas downstream had notably elevated concentrations of Pb, Zn, and, to a lesser extent, Cd and Cu, when compared to nearby control sites. These high trace metal concentrations were mirrored in the body burdens of aquatic invertebrates collected in the contaminated streams both at, and downstream of, the mines. Wood mice collected in contaminated areas appeared to be able to regulate their Zn and Cu tissue concentrations, but, when compared to wood mice from a nearby control site, they had significantly elevated concentrations of Cd and, particularly, Pb, detected in their kidney, liver, and bone samples. The Pb concentrations found in these tissues correlated strongly with local soil concentrations (kidney: ρ = 0.690; liver: ρ = 0.668, bone: ρ = 0.649), and were potentially indicative of Pb toxicity in between 10 % and 82 % of the rodents sampled at the mine sites and in areas downstream. The high trace metal concentrations found in the environment and in common prey species (invertebrates and rodents) indicates that trace metal pollution can have far-reaching, ecosystem-wide health impacts long after the polluting activity has ceased, and far beyond the originating site of the pollution.

The reduced net carbon uptake over Northern Hemisphere land causes the close-to-normal CO2 growth rate in 2021 La Niña.

La Niña climate anomalies have historically been associated with substantial reductions in the atmospheric CO2 growth rate. However, the 2021 La Niña exhibited a unique near-neutral impact on the CO2 growth rate. In this study, we investigate the underlying mechanisms by using an ensemble of net CO2 fluxes constrained by CO2 observations from the Orbiting Carbon Observatory-2 in conjunction with estimates of gross primary production and fire carbon emissions. Our analysis reveals that the close-to-normal atmospheric CO2 growth rate in 2021 was the result of the compensation between increased net carbon uptake over the tropics and reduced net carbon uptake over the Northern Hemisphere mid-latitudes. Specifically, we identify that the extreme drought and warm anomalies in Europe and Asia reduced the net carbon uptake and offset 72% of the increased net carbon uptake over the tropics in 2021. This study contributes to our broader understanding of how regional processes can shape the trajectory of atmospheric CO2 concentration under climate change.

Potent activity of polymyxin B is associated with long-lived super-stoichiometric accumulation mediated by weak-affinity binding to lipid A.

Polymyxins are gram-negative antibiotics that target lipid A, the conserved membrane anchor of lipopolysaccharide in the outer membrane. Despite their clinical importance, the molecular mechanisms underpinning polymyxin activity remain unresolved. Here, we use surface plasmon resonance to kinetically interrogate interactions between polymyxins and lipid A and derive a phenomenological model. Our analyses suggest a lipid A-catalyzed, three-state mechanism for polymyxins: transient binding, membrane insertion, and super-stoichiometric cluster accumulation with a long residence time. Accumulation also occurs for brevicidine, another lipid A-targeting antibacterial molecule. Lipid A modifications that impart polymyxin resistance and a non-bactericidal polymyxin derivative exhibit binding that does not evolve into long-lived species. We propose that transient binding to lipid A permeabilizes the outer membrane and cluster accumulation enables the bactericidal activity of polymyxins. These findings could establish a blueprint for discovery of lipid A-targeting antibiotics and provide a generalizable approach to study interactions with the gram-negative outer membrane.