Biology subjects

Brown, K.

Publications and source records attributed to Brown, K..

At least 37 records · Page 2Linked to original sources

bioRxiv2025

HIV inhibits Warburg metabolism in human macrophages infected with Mycobacterium tuberculosis.

Tuberculosis (TB)-associated mortality remains disproportionately high among people living with HIV (PLWH), with macrophage dysfunction representing a key mechanism of impaired host defence against Mycobacterium tuberculosis (Mtb) infection. Using the U1 chronically HIV-infected macrophage cell line model coupled with primary human monocyte-derived macrophages (MDMs) exposed to HIV-1 gp120, we systematically characterized immunometabolic perturbations during Mtb infection. Nanostring RNA analysis revealed that Mtb monoinfection upregulated glycolytic genes while suppressing oxidative phosphorylation (OXPHOS) transcripts, consistent with a Warburg-type metabolic shift. Conversely, HIV infection downregulated glycolytic enzymes and enhanced mitochondrial respiratory chain components. Coinfection studies demonstrated HIV-mediated suppression of Mtb-induced glycolytic reprogramming. Extracellular flux analysis demonstrated that gp120 exposure increased basal oxygen consumption rate while impairing spare respiratory capacity in Mtb-infected MDMs, effectively blocking the Warburg metabolic transition. Notably, gp120 concentrations equivalent to those observed in antiretroviral therapy (ART)-treated PLWH significantly disrupted metabolic plasticity and high-dose gp120 attenuated Mtb-induced TNF- secretion. ImportanceThis study provides mechanistic insight into HIV-associated susceptibility to TB by demonstrating that HIV-1 infection fundamentally alters macrophage immunometabolic responses to Mtb. We establish that HIV-1, through gp120-mediated signaling, subverts the critical glycolytic induction required for effective antimicrobial responses against Mtb. The persistence of this metabolic dysregulation at clinically relevant gp120 concentrations, comparable to those observed in virologically suppressed PLWH, suggests ongoing immunological vulnerability despite ART. These findings identify HIV-induced metabolic reprogramming as a potential contributor to the persistently elevated TB risk in ART-treated individuals and highlight macrophage immunometabolism as a promising therapeutic target for host-directed therapies in HIV/TB coinfection. The dissociation between metabolic and cytokine responses suggests complex, multifactorial mechanisms underlying HIV-associated impairment of anti-mycobacterial immunity, warranting further investigation into the molecular pathways connecting cellular metabolism and immune effector functions.

immunology↗

bioRxiv2025

Distinct impacts of sodium channel blockers on the strength-duration properties of human motor cortex neurones

Voltage-gated sodium channels (VGSCs) are essential for regulating axonal excitability in the human brain. While sodium channel blockers are known to modulate neuronal excitability, their in vivo effects on the human cortex remain poorly understood. Here, we employed novel transcranial magnetic stimulation (TMS) measures to investigate the effects of sodium channel blockers, carbamazepine and lacosamide, on the strength-duration behaviour of human cortical neurones, serving as an index of sodium channel function. Our data showed that single doses of both medications elevated resting motor thresholds compared to placebo, indicating reduced excitability; however, their impacts varied according to TMS pulse width. Carbamazepine raised thresholds proportionally across all pulse widths, whereas lacosamide disproportionately influenced thresholds for long-duration pulses. Crucially, lacosamide reduced the strength-duration time constant and increased rheobase, while carbamazepine had minimal effects on both. These results reveal subtle and unexpected differences in cortical neurone behaviour following VGSC-blocking medication administration. Lacosamides response aligns with the proposed mechanism of sodium conductance blockade, while carbamazepines effects suggest distinct VGSC interactions or potential off-target effects. Our findings advance the understanding of VGSC-blocking medication interactions in the human cortex and underscore the importance of employing specific TMS measures to gain deeper insights into medication mechanisms of action in vivo. Such measures could serve as valuable adjuncts in medication development and patient monitoring, enhancing understanding of medication action in clinical settings.

neuroscience↗

bioRxiv2024

Peatland restoration can provide climate change mitigation over all time-scales: A UK case-study

Peatlands provide one of the largest terrestrial carbon stocks in the UK. However, a large proportion of peatlands are drained for peat extraction, agriculture and other uses, turning them into a major source of the UKs land use greenhouse gas (GHG) emissions. Successful restoration can ultimately return peatlands into carbon sinks. However, rewetting - the primary step in peatland restoration - can reduce CO2 emissions while increasing CH4 emissions. This may result in little overall climate benefit, or even increased warming for several years post peatland restoration, as CH4 is a short-lived but strong GHG, and may overpower the reduction in CO2. Such consequences are rarely explored in detail, since most studies are based on comparing total CO2-equivalent emissions pre- and post-restoration using the 100-year Global Warming Potential (GWP100), which can fail to reveal the full dynamics. We evaluated the emissions and resultant climate impacts from peatland restoration using data from The Wildlife Trusts, a federation of UK-based conservation charities, as a case-study. The total emissions of each restoration stage were estimated by multiplying peatland areas under restoration with up-to-date UK emission factors (EF), then compared under multiple pulse emission metrics (GWP100, GWP20, GTP100) to indicate the impacts over a range of time-horizons, and GWP* to reveal the varying warming impacts over time. We also used Monte-Carlo Simulation to investigate the uncertainties in total emissions drawing from EF ranges. We found that the restoration so far has provided large emission reductions under all metrics, even considering the uncertainties. Increased CH4 is unlikely to cause extra warming in the extremely near-term (<20 years), and if the peatlands are maintained in their rewetted states, they can contribute to net-cooling in the long term. There is less certainty over the climate benefits of further restoration, from rewetted to "near-natural" states, especially in the shorter term, but we argue that any risks are low, while this continued restoration will provide further ecological benefits and support biodiversity. Our study lends further support for peatland restoration in the UK and other regions with similar habitats, and provides insight into the climate roles of peatlands more broadly.

ecology↗

bioRxiv2024

Uncovering hundreds of exogenous and endogenous RNA viral RdRp sequences amongst uncharacterised sequences in public protein databases

Public databases of protein sequences, such as the National Center for Biotechnology Information (NCBI) Protein repository and UniProt, contain millions of proteins identified in samples from specific species but named as uncharacterised, hypothetical or unclassified due to a lack of information about their function. It has been demonstrated previously that many such sequences show high similarity to genes from RNA viruses, either due to viral infection of the original sample, contamination or endogenous viral elements (EVEs) integrated into the genome of the sample species. Many proteins from RNA virus discovery research are also deposited into these repositories but, for various reasons, can only be labelled as uncharacterised and classified taxonomically at a superkingdom or realm level. Sequences from protein repositories not labelled specifically as being derived from the RNA viral RNA dependent RNA polymerase (RdRp) protein are often used as negative controls when looking to identify viral RdRp sequences, so the presence of unlabelled viruses amongst these datasets is problematic. In this study, we screened uncharacterised proteins from two large public protein repositories - NCBI Protein and UniProt - to identify sequences likely to be derived from RNA viral RdRp. 3,560 such sequences were identified, many derived from EVEs. Many previously unknown EVEs were identified and led to characterisation of additional, related sequences. For example, a group of orbivirus-like viruses infecting nematodes was uncovered which appears to have both ancient endogenous and circulating exogenous members. Many recent integrations of mito-like viruses into plant genomes were identified, indicative of current or recent RNA viral activity. In several taxonomic groups, the first example of an EVE, and in some cases the first example of any RNA virus, was uncovered. The large number of EVEs uncovered by this relatively small-scale search suggests that only a fraction of the true diversity of EVEs is currently known. We also explore uncharacterised proteins further by providing provisional taxonomic annotations for RdRps which are currently only listed as members of the Riboviria realm. A number of sequences are identified which are indistinguishable from known, pathogenic viruses but are labelled as bacteria, seemingly as a result of mislabelling or contamination. Sequences which are not RNA viral but show some similarity to RdRp are also analysed, as a potential source of false positives in virus discovery research. Finally, recommendations are made for generating useful negative controls.

microbiology↗

bioRxiv2024

Responses of root architectural and anatomical traits to low nitrogen stress in rice

Improving nitrogen use efficiency in rice would provide economic and environmental benefits, but little is known about root morphological and anatomical responses to low nitrogen. In this study, two sets of rice genotypes, one set from the RDP1 panel, and one set of recombinant inbred lines, were used to characterize responses to gradual nitrogen depletion by plant uptake and movement of nitrogen to deeper soil strata as a result of leaching, so that more nitrogen was available at depth in aerobic soil mesocosms in a greenhouse. There was significant genetic variation in shoot biomass reductions in response to low nitrogen. The root to shoot biomass ratio was increased by low nitrogen in both sets of genotypes. Relative investment in nodal root number was accentuated with low nitrogen, and shoot biomass was correlated with numbers and lengths of nodal and large lateral roots. There was genetic variation for nodal root number and length in both sets of genotypes. Anatomical responses to low nitrogen were assessed in nodal roots of the RILs, where root cross-sectional area, stele area, and metaxylem vessel number were reduced by low nitrogen, and root diameter was reduced in the RDP1 genotypes. There were significant interactions of nitrogen with genotype for stele area and percent aerenchyma in the RILs. Genetic variation for low nitrogen responses may be useful for selection of rice lines with greater nitrogen acquisition under nitrogen-leaching conditions.

plant biology↗

bioRxiv2024

Quantitative and Kinetic Proteomics Reveal ApoE Isoform-dependent Proteostasis Adaptations in Mouse Brain

Apolipoprotein E (ApoE) polymorphisms modify the risk of neurodegenerative disease with the ApoE4 isoform increasing and ApoE2 isoform decreasing risk relative to the wild-type control ApoE3 isoform. To elucidate how ApoE isoforms alter the proteome, we measured relative protein abundance and turnover in transgenic mice expressing a human ApoE gene (isoform 2, 3, or 4). This data provides insight into how ApoE isoforms affect the in vivo synthesis and degradation of a wide variety of proteins. We identified 4849 proteins and tested for ApoE isoform-dependent changes in the homeostatic regulation of [~]2700 ontologies. In the brain, we found that ApoE4 and ApoE2 both lead to modified regulation of mitochondrial membrane proteins relative to the wild-type control ApoE3. In ApoE4 mice, this regulation is not cohesive suggesting that aerobic respiration is impacted by proteasomal and autophagic dysregulation. ApoE2 mice exhibited a matching change in mitochondrial matrix proteins and the membrane which suggests coordinated maintenance of the entire organelle. In the liver, we did not observe these changes suggesting that the ApoE-effect on proteostasis is amplified in the brain relative to other tissues. Our findings underscore the utility of combining protein abundance and turnover rates to decipher proteome regulatory mechanisms and their potential role in biology.

biochemistry↗

bioRxiv2024

IL-12/IL23 blockade reveals patterns of asynchronous inflammation in pyoderma gangrenosum

Pyoderma gangrenosum (PG) is a rare neutrophilic dermatosis causing chronic and recalcitrant painful ulcerations. Pathogenic mechanisms are yet poorly understood limiting therapeutic options, however, IL-12/IL-23 inhibition via ustekinumab has previously been associated with positive outcomes. We aimed to elucidate the dysregulated immune landscape of PG and lesional skin changes associated with IL-12/IL-23 blockade. We applied spatial transcriptomics and comparative computation analysis on lesional biopsies from two patients obtained before and after IL-12/IL-23 blockade with ustekinumab. Our data indicate lesional PG skin exhibits complex patterns of inflammation, including a not previously described major infiltration of B cells and establishment of tertiary lymphoid structures. In both patients, IL-12/IL-23 blockade led to marked clinical improvement but was associated with amelioration of contrasting inflammatory pathways. Notably, plasma cell markers and tertiary structures were recalcitrant to the treatment regime suggesting that B cells might play a role in the refractory nature of PG.

immunology↗

bioRxiv2024

PBK/TOPK mediates Ikaros, Aiolos and CTCF displacement from mitotic chromosomes and alters chromatin accessibility at selected C2H2-zinc finger protein binding sites

PBK/TOPK is a mitotic kinase implicated in haematological and non-haematological cancers. Here we show that the key haemopoietic regulators Ikaros and Aiolos require PBK-mediated phosphorylation to dissociate from chromosomes in mitosis. Eviction of Ikaros is rapidly reversed by addition of the PBK-inhibitor OTS514, revealing dynamic regulation by kinase and phosphatase activities. To identify more PBK targets, we analysed loss of mitotic phosphorylation events in Pbk-/-preB cells and performed proteomic comparisons on isolated mitotic chromosomes. Among a large pool of C2H2-zinc finger targets, PBK is essential for evicting the CCCTC-binding protein CTCF and zinc finger proteins encoded by Ikzf1, Ikzf3, Znf131 and Zbtb11. PBK-deficient cells were able to divide but showed altered chromatin accessibility and nucleosome positioning consistent with CTCF retention. Our studies reveal that PBK controls the dissociation of selected factors from condensing mitotic chromosomes and contributes to their compaction.

molecular biology↗

bioRxiv2024

Global variation in prior exposure shapes antibody neutralization profiles of SARS-CoV-2 variants up to BA.2.86

The highly mutated SARS-CoV-2 variant, BA.2.86, and its descendants are now the most frequently sequenced variants of SARS-CoV-2. We analyze antibody neutralization data from eight laboratories from the UK, USA, Denmark, and China, including two datasets assessing the effect of XBB.1.5 vaccines, to determine the effect of infection and vaccination history on neutralization of variants up to and including BA.2.86, and produce antibody landscapes to describe these neutralization profiles. We find evidence for lower levels of immune imprinting on pre-Omicron variants in sera collected from Denmark and China, which may be explained by lower levels of circulation of the ancestral variant in these countries, and the use of an inactivated virus vaccine in China.

immunology↗

bioRxiv2024

TSC22D, WNK and NRBP gene families exhibit functional buffering and evolved with Metazoa for macromolecular crowd sensing

The ability to sense and respond to osmotic fluctuations is critical for the maintenance of cellular integrity. Myriad redundancies have evolved across all facets of osmosensing in metazoans, including among water and ion transporters, regulators of cellular morphology, and macromolecular crowding sensors, hampering efforts to gain a clear understanding of how cells respond to rapid water loss. In this study, we harness the power of gene co-essentiality analysis and genome-scale CRISPR-Cas9 screening to identify an unappreciated relationship between TSC22D2, WNK1 and NRBP1 in regulating cell volume homeostasis. Each of these genes have paralogs and are functionally buffered for macromolecular crowd sensing and cell volume control. Within seconds of hyperosmotic stress, TSC22D, WNK and NRBP family members physically associate into cytoplasmic biocondensates, a process that is dependent on intrinsically disordered regions (IDRs). A close examination of these protein families across metazoans reveals that TSC22D genes evolved alongside a domain in NRBPs that specifically binds to TSC22D proteins, which we have termed NbrT (NRBP binding region with TSC22D), and this co-evolution is concomitant with rapid IDR length expansion in WNK family kinases. Our study identifies functions for unrecognized components of the cell volume sensing machinery and reveals that TSC22D, WNK and NRBP genes evolved as cytoplasmic crowding sensors in metazoans to co-regulate rapid cell volume changes in response to osmolarity.

cell biology↗

bioRxiv2024

A novel ilarvirus protein is expressed via stop codon readthrough and suppresses RDR6-dependent RNA silencing

Ilarviruses are a relatively understudied but important group of plant RNA viruses that includes a number of crop pathogens. Their genomes comprise three RNA segments encoding two replicase subunits, movement protein, coat protein (CP), and (in some ilarvirus subgroups) a protein that suppresses RNA silencing. Here we report that, in many ilarviruses, RNA3 encodes an additional protein (termed CP-RT) as a result of ribosomal readthrough of the CP stop codon into a short downstream readthrough (RT) ORF. Using asparagus virus 2 as a model, we find that CP-RT is expressed in planta where it functions as a weak suppressor of RNA silencing. CP-RT expression is essential for persistent systemic infection in leaves and shoot apical meristem. CP-RT function is dependent on a putative zinc-finger motif within RT. Replacing the asparagus virus 2 RT with the RT of an ilarvirus from a different subgroup restored the ability to establish persistent infection. These findings open up a new avenue for research on ilarvirus silencing suppression, persistent meristem invasion and vertical transmission.

plant biology↗

bioRxiv2024

Oncogenic KRASG12D extrinsically induces an immunosuppressive microenvironment in lung adenocarcinoma

Withdrawal StatementThis manuscript has been withdrawn by the authors due to a dispute over co-first authorship that is currently being arbitrated by the medical school at our institution. Therefore, the authors do not wish this work to be cited as reference for the project. Upon completion of the arbitration process, we will take steps to revert the current withdrawn status. If you have any questions, please contact the corresponding author.

cancer biology↗

bioRxiv2023

Genome-wide CRISPR/Cas9 screen identifies MAT2A as a critical host factor for BK Polyomavirus

BK polyomavirus (BKPyV) is a ubiquitous human pathogen that causes major complications for renal transplant patients (polyomavirus-associated nephropathy) and hematopoietic stem cell transplant patients (haemorrhagic cystitis). There are currently no effective antivirals available against BKPyV. As polyomaviruses are small DNA viruses that express very few proteins and utilise host DNA polymerases for their replication, there is limited possibility of targeting viral proteins for therapeutic intervention. As such, there is increasing interest in targeting host pathways to inhibit these viruses. To identify host genes required for BKPyV infection we have conducted the first genome-wide CRISPR/Cas9 screen in BKPyV infected cells. This led to the identification of methionine adenosyltransferase 2A (MAT2A), which we have validated as a host dependency factor for BKPyV infection. MAT2A is a druggable host enzyme that synthesises S-adenosylmethionine, the principal co-factor and methyl donor within cells. We have found that a small molecule inhibitor of MAT2A is a potent antiviral drug inhibiting BKPyV replication, offering a new therapeutic option for treatment of BKPyV diseases.

microbiology↗

bioRxiv2023

A transmission chain linking Mycobacterium ulcerans with Aedes notoscriptus mosquitoes, possums and human Buruli ulcer cases in southeastern Australia

In temperate southeastern Australia over the past two decades there has been a marked progressive increase in human cases of Buruli ulcer, an infection of subcutaneous tissue caused by Mycobacterium ulcerans. Native possums are the major local environmental reservoir of M. ulcerans as they not only develop Buruli lesions but they also shed M. ulcerans in their excreta. However the way humans acquire M. ulcerans from possums has not been determined. Previous case-control studies, insect field surveys and vector competence studies have suggested a role for mosquitoes in M. ulcerans transmission between possums and humans. To explore these links we conducted an extensive, 4-month structured mosquito field survey and four ad hoc field surveys across an area of 350km2 on the Mornington Peninsula, an area endemic for Buruli ulcer to the south of the major metropolitan city of Melbourne. We then compared spatial and temporal patterns of M. ulcerans-positive mosquito occurrence with M. ulcerans-positive possums (established by previous possum excreta surveys) and human Buruli ulcer cases across the region. We used metabarcoding to assess mosquito blood-feeding host preference and to reconstruct M. ulcerans genomes from positive mosquitoes to test epidemiological inferences. We collected 66,325 mosquitoes spanning 26 different species from 180 repeatedly sampled traps over a 4-month period. Culex molestus and Aedes notoscriptus were the dominant species (42% and 35% of trapped mosquitoes, respectively). PCR screening 25% of trapped mosquitoes revealed a significant association between M. ulcerans and Ae. notoscriptus (p<0.0001) with a maximum likelihood estimate (MLE) of 5.88 M. ulcerans positive mosquitoes per 1,000 tested. Using spatial scanning statistics, we also observed significant overlap between clusters of M. ulcerans-positive Ae. notoscriptus, M. ulcerans-positive possum excreta and human Buruli ulcer cases. Metabarcoding analyses of blood-fed Ae. notoscriptus showed individual mosquitoes had fed both on humans and native possums. Enrichment genome sequencing from PCR-positive mosquitoes confirmed shared M. ulcerans genome single-nucleotide polymorphism (SNP) profiles between mosquitoes, possum excreta and clinical human isolates within the same regions. These findings indicate that Ae. notoscriptus likely transmit M. ulcerans in southeastern Australia and highlight mosquito control as a plausible means to control the Buruli ulcer epidemic in our region.

microbiology↗

bioRxiv2023

Genomic regions and candidate genes affect root anatomical traits in diverse rice accessions

Root anatomical traits show significant variation among rice, Oryza sativa L., genotypes and are of interest for improving adaptation to a variety of edaphic, hydrological and nutritional environments in which rice is grown. However, they are difficult to measure and the genetic controls of these traits are not well understood in rice. We conducted genome-wide association (GWA) analyses using moderate- and high-density SNP panels on a diverse rice population to identify genomic regions and candidate genes that control root anatomical traits. We identified 28 genomic regions for metaxylem vessel area and number, root cross-sectional area, stele area, and aerenchyma area. One genomic region associated with metaxylem vessel number and two regions associated with three root thickness-related traits, stele area, root cross-sectional area and metaxylem vessel area, were supported by chromosome-specific GWA using a high-density SNP panel and are regarded as highly significant regions controlling trait variation. Candidate genes in these regions were related to cell differentiation, elongation and division, and secondary cell wall formation. For genomic regions identified in the indica subpopulation, haplotype variation and root anatomical phenotypes were associated with geographic distributions of the accessions, notably the presence of alternate alleles conferring larger diameter roots, stele, and metaxylem vessels in accessions from the indica 2 and indica 3 subgroups originating largely in south and southeast Asia. The identification of genomic regions and candidate genes related to root anatomical traits in a diverse panel of rice varieties deepens our understanding of trait variation and genetic architecture and facilitates the incorporation of favorable alleles into breeding populations. Key message Genomic regions and candidate genes associated with root anatomical traits were identified in Oryza sativa using genome-wide association analyses.

plant biology↗

bioRxiv2023

Loss of MC1R signaling implicates TBX3 in pheomelanogenesis and melanoma predisposition

The human Red Hair Color (RHC) trait is caused by increased pheomelanin (red-yellow) and reduced eumelanin (black-brown) pigment in skin and hair due to diminished melanocortin 1 receptor (MC1R) function. In addition, individuals harboring the RHC trait are predisposed to melanoma development. While MC1R variants have been established as causative of RHC and are a well-defined risk factor for melanoma, it remains unclear mechanistically why decreased MC1R signaling alters pigmentation and increases melanoma susceptibility. Here, we use single-cell RNA-sequencing (scRNA-seq) of melanocytes isolated from RHC mouse models to reveal a Pheomelanin Gene Signature (PGS) comprising genes implicated in melanogenesis and oncogenic transformation. We show that TBX3, a well-known anti-senescence transcription factor implicated in melanoma progression, is part of the PGS and binds both E-box and T-box elements to regulate genes associated with melanogenesis and senescence bypass. Our results provide key insights into mechanisms by which MC1R signaling regulates pigmentation and how individuals with the RHC phenotype are predisposed to melanoma.

genetics↗

bioRxiv2023

Influence of root cortical aerenchyma on the rhizosphere microbiome of field-grown maize

The root anatomical phenotype root cortical aerenchyma (RCA) decreases the metabolic cost of soil exploration and improves plant growth under drought and low soil fertility. RCA may also change the microenvironment of rhizosphere microorganisms by increasing oxygen availability or by reducing carbon rhizodeposition. We tested the hypothesis that plants with contrasting expression of RCA have different rhizosphere prokaryotic communities. Maize inbreds were grown in two field sites, Limpopo Province, South Africa and Pennsylvania, USA, and their rhizosphere soil sampled at flowering. High- and low-nitrogen fertilization was imposed as separate treatments in the experiment in South Africa. The rhizosphere microbial composition of plants with contrasting RCA was characterized by metabarcoding of the 16S rRNA genes. Geographic location was the most important factor related to the composition of rhizosphere microbial communities. In the site in South Africa, RCA explained greater percent of variance (9%) in the composition of microbial communities than genotype (7%). Although other root anatomical and architectural phenotypes were studied as possible cofactors affecting the microbial composition, RCA was among the best significant explanatory variables for the South African site although it was neutral in the Pennsylvania site. High-RCA rhizospheres significantly enriched OTUs of the families Burkholderiaceae (in South Africa) and Bacillaceae (in USA), compared to low-RCA plants, and OTUs of the families Beijerinckiaceae and Sphingomonadaceae were enriched at the two nitrogen levels in high RCA plants in South Africa. Our results are consistent with the hypothesis that RCA is an important factor for rhizosphere microbial communities, especially under suboptimal nitrogen conditions.

plant biology↗

bioRxiv2023

Bacterial mechanosensing of surface stiffness promotes signaling and growth leading to biofilm formation by Pseudomonas aeruginosa

The attachment of bacteria onto a surface, consequent signaling, and the accumulation and growth of the surface-bound bacterial population are key initial steps in the formation of pathogenic biofilms. While recent reports have hinted that the stiffness of a surface may affect the accumulation of bacteria on that surface, the processes that underlie bacterial perception of and response to surface stiffness are unknown. Furthermore, whether, and how, the surface stiffness impacts biofilm development, after initial accumulation, is not known. We use thin and thick hydrogels to create stiff and soft composite materials, respectively, with the same surface chemistry. Using quantitative microscopy, we find that the accumulation, motility, and growth of the opportunistic human pathogen Pseudomonas aeruginosa respond to surface stiffness, and that these are linked through cyclic-di-GMP signaling that depends on surface stiffness. The mechanical cue stemming from surface stiffness is elucidated using finite-element modeling combined with experiments - adhesion to stiffer surfaces results in greater changes in mechanical stress and strain in the bacterial envelope than does adhesion to softer surfaces with identical surface chemistry. The cell-surface-exposed protein PilY1 acts as a mechanosensor, that upon surface engagement, results in higher cyclic-di-GMP levels, lower motility, and greater accumulation on stiffer surfaces. PilY1 impacts the biofilm lag phase, which is extended for bacteria attaching to stiffer surfaces. This study shows clear evidence that bacteria actively respond to different stiffness of surfaces where they adhere via perceiving varied mechanical stress and strain upon surface engagement. ImportanceBacteria colonize many types of biological and medical surfaces with a large range of stiffnesses. Colonization leads to the formation of biofilms, which cause costly and life-impairing chronic infections. However, whether and how bacteria can sense and respond to the mechanical cue provided by surface stiffness has remained unknown. We find that bacteria do indeed respond to surface stiffness in a way that is both consistent with expectations based on equilibrium continuum mechanics and that quantitatively impacts multiple aspects of early biofilm formation. This is a new understanding for the nascent field of bacterial mechanobiology. Furthermore, this finding suggests the possibility of a new category of approaches to hindering biofilm development by tuning the mechanical properties of biomedical surfaces.

microbiology↗