Biology subjects

Singh, P. K.

Publications and source records attributed to Singh, P. K..

At least 55 records · Page 3Linked to original sources

bioRxiv2022

A pandemic clonal lineage of the wheat blast fungus

Wheat, the most important food crop, is threatened by a blast disease pandemic. Here, we show that a clonal lineage of the wheat blast fungus recently spread to Asia and Africa following two independent introductions from South America. Through a combination of genome analyses and laboratory experiments, we show that the decade-old blast pandemic lineage can be controlled by the Rmg8 disease resistance gene and is sensitive to strobilurin fungicides. However, we also highlight the potential of the pandemic clone to evolve fungicide-insensitive variants and sexually recombine with African lineages. This underscores the urgent need for genomic surveillance to track and mitigate the spread of wheat blast outside of South America, and to guide pre-emptive wheat breeding for blast resistance.

evolutionary biology↗

bioRxiv2022

Multivalent interactions essential for lentiviral integrase function

A multimer of retroviral integrase (IN) synapses viral DNA ends within a stable intasome nucleoprotein complex for integration into a host cell genome. Reconstitution of the intasome from the maedi-visna virus (MVV), an ovine lentivirus, revealed a large assembly containing sixteen IN subunits (1). Herein, we report cryo-EM structures of the lentiviral intasome prior to engagement of target DNA and following strand transfer, refined at 3.4 and 3.5 [A] resolution, respectively. The structures elucidate details of the protein-protein and protein-DNA interfaces involved in lentiviral intasome formation. We show that the homomeric interfaces involved in IN hexadecamer formation and the -helical configuration of the linker connecting the C-terminal and catalytic core domains are critical for MVV IN strand transfer activity in vitro and for virus infectivity. Single-molecule microscopy in conjunction with photobleaching revealed that the MVV intasome can bind a variable number, up to sixteen molecules, of the lentivirus-specific host factor LEDGF/p75. Concordantly, ablation of endogenous LEDGF/p75 resulted in gross redistribution of MVV integration sites in human and ovine cells. Our data confirm the importance of the expanded architecture observed in cryo-EM studies of lentiviral intasomes and suggest that this organization underlies multivalent interactions with chromatin for integration targeting to active genes.

biochemistry↗

bioRxiv2021

Are members of the Anopheles fluviatilis complex conspecific?

Anopheles fluviatilis sensu lato, a primary malaria vector in India, was identified to be comprised of four cryptic species, provisionally designated as species S, T, U and V. However, Kumar et al. (Mol Ecol Resour, 2013;13:354-61) considered all of the then known three members of this species complex (S, T and U) conspecific. The specific status of species S and T was refuted based on the lack of sufficient barcode gap in mitochondrial-CO1 and the perceived presence of heterozygotes in populations as detected through one of the two species-specific PCR assays employed for the cryptic species identification. The existence of species U was refuted claiming that earlier investigations have already refuted their existence. This conclusion is concerning because of the differential public health implications of members of the Fluviatilis Complex. Here we discuss problems associated with the CO1-based barcode approach for delimitation of cryptic species, the perceived heterozygosity between species S and T based on a species-specific PCR assay, and interpretation of published reports. We demonstrated that fixed differences do exist in the ITS2-rDNA sequence of species S and T with no evidence of heterozygotes in sympatric populations and, that the observed heterozygosity by Kumar et al. in the ITS2-based species diagnostic PCR is due to the high mispriming tendency of the T-specific primer with species S. We infer that mitochondrial DNA-based barcoding gap, an arbitrary threshold recommended for species delimitation, alone, is inadequate to delimit the members of An. fluviatilis complex.

molecular biology↗

bioRxiv2021

Exploring the metabolic landscape of pancreatic ductal adenocarcinoma cells using genome-scale metabolic modeling

Pancreatic ductal adenocarcinoma (PDAC) is a major research focus due to its poor therapy response and dismal prognosis. PDAC cells adapt their metabolism efficiently to the environment to which they are exposed, often relying on diverse fuel sources depending on availability. Since traditional experimental techniques appear exhaustive in the search for a viable therapeutic strategy against PDAC, in this study, a highly curated and omics-informed genome-scale metabolic model of PDAC was reconstructed using patient-specific transcriptomic data. From the analysis of the model-predicted metabolic changes, several new metabolic functions were explored as potential therapeutic targets against PDAC in addition to the already known metabolic hallmarks of pancreatic cancer. Significant downregulation in the peroxisomal fatty acid beta oxidation pathway reactions, flux modulation in the carnitine shuttle system, and upregulation in the reactive oxygen species detoxification pathway reactions were observed. These unique metabolic traits of PDAC were then correlated with potential drug combinations that can be repurposed for targeting genes with poor prognosis in PDAC. Overall, these studies provide a better understanding of the metabolic vulnerabilities in PDAC and will lead to novel effective therapeutic strategies. Author summaryPancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer, with late diagnosis, early metastasis, insufficient therapy response, and very low survival rates. Due to these challenges associated with the diagnosis and treatment of PDAC, it has been a research area of interest. With the goal of understanding the metabolic reprogramming in proliferating PDAC cells, we reconstructed healthy and PDAC models by incorporating patient transcriptomic data into a genome-scale global human metabolic model. Comparing the metabolic flux space for the reactions in the two context-specific models, we identified significantly divergent pathways in PDAC. These results allowed us to further investigate growth-limiting genes in PDAC and identify potential drug combinations that can be repositioned for treatment of PDAC.

systems biology↗

bioRxiv2021

A Population-level Strain Genotyping Method to Study Pathogen Strain Dynamics in Human Infections

A hallmark of chronic bacterial infections is the long-term persistence of one or more pathogen species at the compromised site. Repeated detection of the same bacterial species can suggest that a single strain or lineage is continually present. However, infection with multiple strains of a given species, strain acquisition and loss, and changes in strain relative abundance can occur. Detecting strain-level changes and their effects on disease is challenging as most methods require labor intensive isolate-by-isolate analyses, thus, only a few cells from large infecting populations can be examined. Here we present a population-level method for enumerating and measuring the relative abundance of strains called "PopMLST". The method exploits PCR amplification of strain-identifying polymorphic loci, next-generation sequencing to measure allelic variants, and informatic methods to determine whether variants arise from sequencing errors or low abundance strains. These features enable PopMLST to simultaneously interrogate hundreds of bacterial cells that are either cultured en masse from patient samples, or are present in DNA directly extracted from clinical specimens without ex vivo culture. This method could be used to detect epidemic or super-infecting strains, facilitate understanding of strain dynamics during chronic infections, and enable studies that link strain changes to clinical outcomes.

microbiology↗

bioRxiv2021

The depletion mechanism can actuate bacterial aggregation by self-produced exopolysaccharides and determine species distribution and composition in bacterial aggregates

Bacteria causing chronic infections are often found in cell aggregates suspended in polymer secretions, and aggregation may be a factor in infection persistence. One aggregation mechanism, called depletion aggregation, is driven by physical forces between bacteria and polymers. Here we investigated whether the depletion mechanism can actuate the aggregating effects of P. aeruginosa exopolysaccharides for suspended (i.e. not surface attached) bacteria, and how depletion affects bacterial inter-species interactions. We found cells overexpressing the exopolysaccharides Pel and Psl, but not alginate remained aggregated after depletion-mediating conditions were reversed. In co-culture, depletion aggregation had contrasting effects on P. aeruginosas interactions with coccus- and rod-shaped bacteria. Depletion caused S. aureus (cocci) and P. aeruginosa (rods) to segregate from each other, S. aureus to resist secreted P. aeruginosa antimicrobial factors, and the species to co-exist. In contrast, depletion aggregation caused P. aeruginosa and Burkholderia sp. to intermix, enhancing type VI secretion inhibition of Burkholderia by P. aeruginosa, leading to P. aeruginosa dominance. These results show that in addition to being a primary cause of aggregation in polymer-rich suspensions, physical forces inherent to the depletion mechanism can actuate the aggregating effects of self-produced exopolysaccharides and determine species distribution and composition of bacterial communities.

microbiology↗

bioRxiv2021

Vibrio cholerae biofilm dispersal regulator causes cell release from matrix through type IV pilus retraction

The extracellular matrix is a defining feature of bacterial biofilms and provides structural stability to the community by binding cells to the surface and to each other. Transitions between bacterial biofilm initiation, growth, and dispersion require different regulatory programs, all of which result in modifications to the extracellular matrix composition, abundance, or functionality. However, the mechanisms by which individual cells in biofilms disengage from the matrix to enable their departure during biofilm dispersal are unclear. Here, we investigated active biofilm dispersal of Vibrio cholerae during nutrient starvation, resulting in the discovery of the conserved Vibrio biofilm dispersal regulator VbdR. We show that VbdR triggers biofilm dispersal by controlling cellular release from the biofilm matrix, which is achieved by inducing the retraction of the mannose-sensitive hemagglutinin (MSHA) type IV pili and the expression of a matrix protease IvaP. We further show that MSHA pili have numerous binding partners in the matrix and that the joint effect of MSHA pilus retraction and IvaP activity is necessary and sufficient for causing biofilm dispersal. These results highlight the crucial role of type IV pilus dynamics during biofilm dispersal and provide a new target for controlling V. cholerae biofilm abundance through the induction and manipulation of biofilm dispersal.

microbiology↗

bioRxiv2021

Contrasting processing tomato cultivars unlink yield and pollen viability under heat stress

The occurring climate change is causing temperature increment in crop production areas worldwide, generating conditions of heat stress that negatively affect crop productivity. Tomato (Solanum lycopersicum), a major vegetable crop, is highly susceptible to conditions of heat stress. When tomato plants are exposed to ambient day/night temperatures that exceed 32{degrees}C/20{degrees}C respectively during the reproductive phase, fruit set and fruit weight are reduced, leading to a significant decrease in yield. Processing tomato cultivars are cultivated in open fields, where environmental conditions are not controlled, therefore plants are exposed to multiple abiotic stresses, including heat stress. Understanding the physiological response of modern processing tomato cultivars to heat stress may facilitate the development of thermotolerant cultivars. Here, we compared two tomato processing cultivars, H4107 and H9780, that we found to be constantly differing in yield performance. Using field and temperature-controlled greenhouse experiments, we show that the observed difference in yield is attributed to the occurrence of heat stress conditions. In addition, fruit-set and seed production were significantly improved in the thermotolerant cultivar H4107, compared with H9780. Despite the general acceptance of pollen viability as a measure of thermotolerance, there was no difference in the percentage of viable pollen between H4107 and H9780 under either of the conditions tested. Therefore, processing tomato cultivars may present a particular case, in which other factors are central for heat stress tolerance. Our results also demonstrate the value of combining controlled with uncontrolled experimental settings, in order to identify heat stress related responses and facilitate the development of thermotolerant processing tomato cultivars.

plant biology↗

bioRxiv2021

The Actin Bundling Protein Fascin Promotes Lung Cancer Growth and Metastasis by Enhancing Glycolysis and PFKFB3 Expression

Fascin is a pro-metastasis actin bundling protein upregulated in essentially all the metastatic carcinoma. It is believed that fascin promotes cancer cell migration and invasion by facilitating membrane protrusions such as filopodia and invadopodia. Aerobic glycolysis is a key feature of cancer metabolism that provides critical intermediate metabolites for tumor growth and cell proliferation. Here we report that fascin increase glycolysis in lung cancer to promote tumor growth and metastasis. Fascin promotes glycolytic flux by increasing the expression and activities of phosphofructose kinase 1 and 2 (PFK1 and 2). The glycolytic function of fascin depends on activation of YAP1 through its canonical actin bundling activity. Fascin promotes the binding of YAP1 to a TEAD1/4 binding motif located 30 bp upstream of the PFKFB3 transcription start site to activate its transcription. Our interrogation of the TCGA database suggest that the fascin-YAP1-PFKFB3 circuit is likely conserved across different types of cancer. We further showed that the glycolytic function of fascin is essential for promotion of lung cancer growth and metastasis. Importantly, pharmacological inhibitors of fascin could be used to suppress the YAP1-PFKFB3 signaling and inhibit glycolysis in cancer cell lines, organoid cultures and xenograft metastasis models. Taken together, our data reveal an important glycolytic role of fascin in lung cancer metabolism, and suggest that pharmacological inhibitors of fascin could be used to reprogram cancer metabolism in lung cancer and potentially other cancer with fascin upregulation.

cancer biology↗

bioRxiv2021

Indoleamine 2,3-dioxygenase upregulates PD-1 expression on ovarian tumor infiltrating CD8+ T cells via kynurenine activation of the aryl hydrocarbon receptor

The immunoregulatory enzyme, indoleamine 2,3-dioxygenase (IDO1) and the PD-1/PD-L1 axis are potent mechanisms that impede effective anti-tumor immunity in ovarian cancer. However, whether the IDO pathway regulates PD-1 expression in T cells is currently unknown. Here we show that tumoral IDO1 expression led to profound changes in tryptophan, nicotinate/nicotinamide, and purine metabolic pathways in the ovarian tumor microenvironment, and to an increased frequency of PD-1+CD8+ tumor infiltrating T cells. We determined that activation of the aryl hydrocarbon receptor (AHR) by kynurenine induced PD-1 expression, and this effect was significantly abrogated by the AHR antagonist CH223191. Mechanistically, kynurenine alters chromatin accessibility in regulatory regions of T cell inhibitory receptors, allowing AHR to bind to consensus XRE motifs in the promoter region of PD-1. These results enable the design of strategies to target the IDO1 and AHR pathways for enhancing anti-tumor immunity in ovarian cancer.

immunology↗

bioRxiv2020

Matrix-trapped viruses can protect bacterial biofilms from invasion by colonizing cells

Bacteria often live in the context of spatially restricted groups held together by a self-secreted, adhesive extracellular matrix. These groups, termed biofilms, are likely where many phage-bacteria encounters occur. A number of recent studies have documented that phages can be trapped in the outer matrix layers of biofilms, such that the bacteria inside are protected from exposure. It is not known, however, what might happen after this: are the trapped phages still viable on the biofilm exterior? If so, do they pose a threat to newly arriving cells that might otherwise colonize the existing biofilm? Here we set out to address these questions using a biofilm-producing strain of Escherichia coli and its lytic phage T7. Prior work has demonstrated that T7 phages are trapped in the outermost layers of curli polymers within the E. coli matrix. We show that these phages do remain viable and kill incoming colonizing cells so long as they are T7-susceptible. If colonizing cells arrive to the outside of a resident biofilm before phages do, they can still be killed by phage exposure if it occurs soon thereafter. However, if colonizing cells are present on the biofilm long enough before phage exposure, they gain phage protection via envelopment within curli-producing clusters of the resident biofilm cells. This work establishes that phages trapped in the outer matrix layers of a resident biofilm can be incidentally weaponized as a mode of protection from competition by newly arriving cells that might otherwise colonize the biofilm exterior.

microbiology↗

bioRxiv2020

Impact of clade specific mutations on structural fidelity of SARS-CoV-2 proteins

The SARS-CoV-2 is a positive stranded RNA virus with a genome size of ~29.9 kilobase pairs which spans 29 open reading frames. Studies have revealed that the genome encodes about 16 non-structural proteins (nsp), four structural proteins, and six or seven accessory proteins. Based on prevalent knowledge on SARS-CoV and other coronaviruses, functions have been assigned for majority of the proteins. While, researchers across the globe are engrossed in identifying a potential pharmacological intervention to control the viral outbreak, none of the work has come up with new antiviral drugs or vaccines yet. One possible approach that has shown some positive results is by treating infected patients with the plasma collected from convalescent COVID-19 patients. Several vaccines around the world have entered their final trial phase in humans and we expect that these will in time be available for application to worldwide population to combat the disease. In this work we analyse the effect of prevalent mutations in the major pathogenesis related proteins of SARS-COV2 and attempt to pinpoint the effects of those mutations on the structural stability of the proteins. Our observations and analysis direct us to identify that all the major mutations have a negative impact in context of stability of the viral proteins under study and the mutant proteins suffer both structural and functional alterations as a result of the mutations. Our binary scoring scheme identifies L84S mutation in ORF8 as the most disruptive of the mutations under study. We believe that, the virus is under the influence of an evolutionary phenomenon similar to Mullers ratchet where the continuous accumulation of these mutations is making the virus less virulent which may also explain the reduction in fatality rates worldwide.

bioinformatics↗

bioRxiv2020

Reduced NCOR2 expression accelerates androgen deprivation therapy failure in prostate cancer

NCOR2 is frequently and significantly mutated in late stage androgen deprivation therapy resistant prostate cancer (ADT-RPCa). NCOR2 has been characterized as a transcriptional corepressor and has mechanistic links to DNA methylation, but its global functions and overall contributions to PCa progression remain enigmatic. In the current study, we utilize immunohistochemical staining of samples from over 700 PCa patients and reveal associations of reduced NCOR2 expression with correlates of aggressive primary PCa and recurrence in patients who received adjuvant androgen deprivation therapy. We mapped the dihydrotestosterone (DHT) dependent and independent effects of NCOR2 on the transcriptome, cistrome and DNA methylome in androgen sensitive (AS) and ADT-RPCa cells using the isogenic LNCaP and LNCaP-C4-2 (C4-2) cell models. Transcriptional profiling identified androgen dependent and independent regulatory roles of NCOR2, the latter of which was enhanced in the ADT-RPCa state and included neuronal differentiation. Interestingly, reduced expression of NCOR2 resulted in a striking global DNA hypermethylation pattern that significantly enriched at enhancer regions. ChIP-seq revealed that NCOR2 was more clearly associated with promoters in AS LNCaP cells, which was modestly enhanced by DHT treatment. However, in ADT-RPCa C4-2 cells, the NCOR2 cistrome was larger and more distal. Motif analyses and integration of large-scale public cistrome data revealed strong enrichment for FOXA1 in mediating NCOR2 binding, and included additional factors such as AR, E2F, TET2, MED1 and MBD2. Utilizing the CWR22 xenograft model, we demonstrate a direct role for NCOR2 in PCa progression as reduced NCOR2 expression attenuated the impact of ADT, and significantly accelerated recurrence of disease. Transcriptomic analyses in recurrent CWR22 tumors indicated NCOR2-dependent gene expression profiles during ADT that were enriched for neuroendocrine associated genes and also associated with worse survival in human patients with ADT-RPCa. DNA methylation profiles in CWR22 tumors with reduced NCOR2 expression recapitulated the hypermethylation observed in vitro, and further revealed that hypermethylation patterns are commonly associated with ADT-RPCa disease, which was also confirmed in human samples. These studies reveal robust roles for NCOR2 in regulating the PCa transcriptome and epigenome and underscore recent mutational studies linking NCOR2 loss of function to PCa disease progression.Competing Interest StatementThe authors have declared no competing interest.View Full Text

cancer biology↗

bioRxiv2020

Hypoxia driven oncometabolite L-2HG maintains "stemness"-differentiation balance and facilitates immune suppression in pancreatic cancer

2-hydroxyglutarate (2-HG) has gained considerable importance in glioma and blood cancers that have mutations in the IDH1/2 gene. In the current study we show for the first time that pancreatic tumors produce 2HG in the absence of IDH1/2 mutation. Our study shows that hypoxic pancreatic tumors that have activated lactate dehydrogenase (LDH) activity, produce the L-isoform of 2HG. Metabolic mass spectrometric analysis along with chiral derivatization showed that pancreatic cancer cells as well as stromal cells secrete the L-isomeric form of 2-hydroxyglutarate (L-2HG) when exposed to hypoxic environment. Serum analysis of human pancreatic cancer patients also showed similar accumulation of L-2HG. Our results showed that this abnormally accumulated L-2HG regulates self-renewal by increasing expression of genes associated with stemness (Sox-2, CD133) and by decreasing expression of differentiation genes (Pdx-1, HB9, NKX6.1). Further analysis showed that secreted L-2HG mediates cross talk with immune T-cells and hampers their proliferation and migration thereby suppressing the anti-tumor immunity. In vivo targeting of LDH enzyme with inhibitor (GSK2837808A) showed decrease in L-2HG as well as subsequent tumor regression and sensitization to immune-checkpoint therapy. Present study shows for the first time that hypoxia mediated accumulation of L-2HG drives self-renewal in pancreatic cancer by shifting critical balance of gene expression towards stemness and promotes immune suppression by impairing T cell activation in this disease. Additionally, it indicates that targeting LDH can sensitize pancreatic tumors to anti-PD1 therapy by decreasing L-2HG and reverting their immune evasive function.

cancer biology↗

bioRxiv2019

Tuft cells restrain pancreatic tumorigenesis through paracrine eicosanoid signaling

Despite numerous advances in our understanding of pancreatic ductal adenocarcinoma (PDA) genetics and biology, this disease is expected to become the second leading cause of cancer-related U.S. deaths within the next few years. Incomplete understanding of how it arises precludes development of early detection and interception strategies to improve therapeutic outcomes. Acinar to ductal metaplasia involving genesis of tuft cells is one early step in PDA formation, but their functional significance has remained obscure due to their rarity and a lack of methods and relevant animal models for their molecular and functional analysis. Here, we show that deletion of tuft cell master regulator Pou2f3 eliminates pancreatic tuft cells and increases fibrosis, alters immune cell activation, and accelerates disease progression. We demonstrate that tuft cell expression of the prostaglandin D2 synthase Hpgds restrains pancreatic disease progression in early stages by inhibiting stromal activation. Analyses of human data sets are consistent with mouse studies. We propose that tuft cells and, by inference, the associated metaplastic lesions, play a protective role early in pancreatic tumorigenesis. SignificanceWe find that tuft cell formation in response to oncogenic Kras is protective and restrains tumorigenesis through local production of anti-inflammatory substances, including paracrine prostaglandin D2 signaling to the stroma. Our findings establish tuft cells as a metaplasia-induced tumor suppressive cell type.

cancer biology↗

bioRxiv2019

Paradoxical role of AT-rich interactive domain 1A in restraining pancreatic carcinogenesis

Background & AimsARID1A is postulated to be a tumor suppressor gene owing to loss-of-function mutations in human pancreatic ductal adenocarcinomas (PDAC). However, its role in pancreatic pathogenesis is not clear despite recent studies using genetically engineered mouse (GEM) models. We aimed at further understanding of its direct functional role in PDAC, using a combination of GEM model, PDAC cell lines. MethodsPancreas-specific mutant Arid1a-driven GEM model (Ptf1a-Cre;KrasG12D;Arid1af/f or "KAC") was generated by crossing Ptf1a-Cre;KrasG12D ("KC") mice with Arid1af/f mice and characterized histologically with timed necropsies. Arid1a was also deleted using CRISPR-Cas9 system in established PDAC cell lines to study the immediate effects of Arid1a loss in isogenic models. Cells lines with or without Arid1a expression were developed from respective autochthonous PDAC GEM models, compared functionally using various culture assays, and subjected to RNA-sequencing for comparative gene expression analysis. DNA damage repair was analyzed in cultured cells using immunofluorescence and COMET assay. ResultsArid1a is critical for early progression of mutant Kras-driven pre-malignant lesions into PDAC, as evident by lower Ki-67 and higher apoptosis staining in "KAC" as compared to "KC" mice. Enforced deletion of Arid1a in established PDAC cell lines caused suppression of cellular growth and migration, accompanied by compromised DNA damage repair. Despite early development of relatively indolent cystic precursor lesions called intraductal papillary mucinous neoplasms (IPMNs), a subset of "KAC" mice developed aggressive PDAC in later ages. PDAC cells obtained from older autochthonous "KAC" mice revealed epigenetic changes underlying the various compensatory mechanisms to overcome the growth suppressive effects of Arid1a loss. ConclusionsArid1a is an essential survival gene whose loss impairs cellular growth, and thus, its expression is critical during early stages of pancreatic tumorigenesis in mouse models.

cancer biology↗

bioRxiv2019

BiofilmQ, a software tool for quantitative image analysis of microbial biofilm communities

Biofilms are now considered to be the most abundant form of microbial life on Earth, playing critical roles in biogeochemical cycles, agriculture, and health care. Phenotypic and genotypic variations in biofilms generally occur in three-dimensional space and time, and biofilms are therefore often investigated using microscopy. However, the quantitative analysis of microscopy images presents a key obstacle in phenotyping biofilm communities and single-cell heterogeneity inside biofilms. Here, we present BiofilmQ, a comprehensive image cytometry software tool for the automated high-throughput quantification and visualization of 3D and 2D community properties in space and time. Using BiofilmQ does not require prior knowledge of programming or image processing and provides a user-friendly graphical user interface, resulting in editable publication-quality figures. BiofilmQ is designed for handling fluorescence images of any spatially structured microbial community and growth geometry, including microscopic, mesoscopic, macroscopic colonies and aggregates, as well as bacterial biofilms in the context of eukaryotic hosts.

microbiology↗

bioRxiv2019

Flow-induced symmetry breaking in growing bacterial biofilms

Bacterial biofilms represent a major form of microbial life on Earth and serve as a model active nematic system, in which activity results from growth of the rod-shaped bacterial cells. In their natural environments, ranging from human organs to industrial pipelines, biofilms have evolved to grow robustly under significant fluid shear. Despite intense practical and theoretical interest, it is unclear how strong fluid flow alters the local and global architectures of biofilms. Here, we combine highly time-resolved single-cell live imaging with 3D multi-scale modeling to investigate the mechanisms by which flow affects the dynamics of all individual cells in growing biofilms. Our experiments and cell-based simulations reveal three quantitatively different growth phases in strong external flow, and the transitions between them. In the initial stages of biofilm development, flow induces a downstream gradient in cell orientation, causing asymmetrical droplet-like biofilm shapes. In the later developmental stages, when the majority of cells are sheltered from the flow by the surrounding extracellular matrix, buckling-induced cell verticalization in the biofilm core restores radially symmetric biofilm growth, in agreement with predictions of a 3D continuum model.

biophysics↗