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Biology subjects

Gopal, P.

Publications and source records attributed to Gopal, P..

16 recordsLinked to original sources

Nucleoporin 50a interacts with geminivirus C4 proteins and contributes to infection

Geminiviruses are plant DNA viruses that replicate in the nucleus of the host cell and rely on the host nucleocytoplasmic transport machinery to complete their infection cycle. While various geminiviral proteins have been reported to interact with plant transport factors, the contribution of nuclear pore complex components to geminivirus infection remains largely unexplored. Here, we identify nucleoporin 50a (NUP50a) as a previously unreported host factor that contributes to bhendi yellow vein mosaic virus (BYVMV) infection. Affinity purification coupled with mass spectrometry isolated NUP50a as a potential interactor of the BYVMV pathogenicity determinant C4, which was further validated by pull-down and co-immunoprecipitation assays. Yeast two-hybrid assays, bimolecular fluorescence complementation, and colocalization analysis demonstrated that BYVMV C4 directly associates with NUP50a predominantly in the nucleus. Virus-induced gene silencing of NbNUP50a significantly delayed symptom development and reduced viral DNA accumulation, suggesting that NUP50a is required for efficient BYVMV infection. Silencing NbNUP50a did not influence the subcellular localization of BYVMV C4, indicating that the role of NUP50a extends beyond determining C4 steady-state localization. Notably, NUP50a was found to associate with C4 proteins from three additional geminiviruses, supporting the possibility that targeting NUP50a represents a characteristic strategy among geminiviruses. Together, our findings provide evidence of a nuclear pore complex member involved in geminivirus pathogenesis. These results establish a framework for further study of the potential transport-dependent and/or transport-independent functions of NUP50a during viral infection.

plant biology↗

Decoding Spatial Programs in Human Glioblastoma Through Surprisal Information-Theoretical Analysis

Glioblastoma (GBM) is a highly heterogeneous and invasive brain tumor in which complex interactions among tumor cells, immune cells, and neurons shape disease progression and therapeutic resistance. Resolving spatial patterns programs in glioblastoma (GBM) requires analytical approaches that go beyond variance-driven embeddings. Here, we applied thermodynamic surprisal analysis, an information-theoretic decomposition framework, to spatial transcriptomic sequencing from human GBM specimens to identify orthogonal constraint modes that capture dominant and previously hidden spatial programs. Surprisal analysis revealed structured patterns in the data that are not highlighted by standard approaches such as PCA or cell type deconvolution, including immune-activation-associated signatures as well as spatial programs consistent with synapse remodeling. Coupling surprisal decomposition with spatial ligand-receptor interaction analysis, NICHES, along with multiplexed protein imaging connected these spatial hidden modes to reveal potential communication networks. Together, these results position surprisal analysis as a powerful, complementary strategy for interrogating spatial tumor architecture, enabling discovery of non-obvious spatial programs and interactions that are obscured by variance-based methods.

systems biology↗

Resolving phenotyping discordance with SPACEMAP, an integrated machine learning framework

Multiplex imaging technologies have revolutionized our ability to study cellular behavior within the tissue microenvironment. Translating this complex data into meaningful biological insights requires a unified analytical framework. To address this, we developed SPACEMAP (Spatial Phenotyping And Classification with Enhanced Multiplex Analysis Pipeline), a comprehensive Python and Qupath-based platform for multiplex imaging analysis. SPACEMAP integrates image registration, segmentation, artifact removal, tissue and zone classification, spatial feature extraction, and a consolidated phenotyping approach into a single system. A core feature of SPACEMAP is its high-fidelity phenotyping. To evaluate classification performance, we benchmarked our method RESOLVE, against three established approaches, Leiden clustering, Self-Organizing Maps, and SCIMAP revealing substantial disagreement among them. SPACEMAP overcomes this through two complementary workflows: a machine learning model trained on expert-labeled cells, and a consensus classifier that integrates high-confidence cells across methods. Here, we validated SPACEMAP on in-house colorectal cancer samples and a public dataset, demonstrating its robustness.

bioinformatics↗

Distinct Filament Conformation for Receptor-Bound Amyloid-β from Alzheimers Disease Brain

Alzheimers disease is triggered by amyloid-{beta}, with symptoms linked to synapse loss. Oligomeric amyloid-{beta}, rather than monomeric or fibrillar amyloid-{beta}, has been proposed to be the proximate mechanistic cause, but the relevant molecular characteristics have remained unclear. Here, we define a distinct receptor-bound amyloid-{beta} pool in Alzheimers brain by release with a receptor antagonist and purification to homogeneity. Receptor-bound amyloid-{beta} is ten times more abundant than free unbound amyloid-{beta}. The amyloid-{beta} associated with receptor is composed of 65 nm long filaments with prion protein binding at its tips. There is no evidence for an oligomeric A{beta} state interacting with human brain receptors. Cryo-electron microscopy shows two symmetric S-shaped monomers per filament rung. The tilt between rung monomers, twist along the filament axis, amino terminal conformation and amyloid seeding properties distinguish this structure from plaque-associated amyloid-{beta} filaments of the same brain. High tip:length ratio is critical for prion protein receptor interaction and synaptic damage. Characterizing receptor-bound amyloid-{beta} filament provides insight into neuronal dysfunction separate from plaque aggregation.

neuroscience↗

Bacteria-induced colitis in naked mole rats is alleviated by probiotic treatment: a new mammalian model for acute inflammatory disease

Enteropathogenic bacteria are a major cause of morbidity and mortality globally. Mouse models have been indispensable in advancing our understanding of infectious diseases caused by intestinal pathogens and in identifying physical, chemical and immunological barriers that limit these infections. However, there are significant differences between laboratory mice and human intestinal microbiota and immunobiology that underscore the need to develop other models that recapitulate the disease pathology and mucosal immune responses of human enteric diseases. Here we report how the pathogenic expansion of Citrobacter braakii in naked mole rats (NMRs) leads to colonic inflammation and epithelial injury that mimics pathological features of human hemorrhagic colitis. We observe mucosal erosions, ulcerations, depletion of goblet cells, extension of proliferative compartments to the surface of the glands, and active inflammation in the colonic lamina propria of infected NMRs. Without intervention, systemic inflammation associated with sepsis ensues in infected NMRs and results in high mortality. Interestingly, we demonstrate a strong therapeutic effect of probiotics comprising Lactobacillus, Bifidobacterium, Streptococcus salvarius subsp. thermophilus and Enterococcus faecium strains. Treatment with probiotics induces mucosal healing and restores intestinal homeostasis, including suppression of excessive proliferation of epithelial cells, replenishment of goblet cells and also has an anti-inflammatory effect. Taken together, we demonstrate that NMRs, beyond their use as an anti-ageing and disease-resistance model, can also be used to address disease mechanisms underlying infectious colitis, including disruptions in the mucosal barrier permeability, gut microbial ecology and in local and systemic immune regulation; and in testing functional probiotics strains as potential therapeutics.

pathology↗

Mechanistic basis for protection against fatty liver disease by CIDEB loss-of-function mutations

Background & AimsSomatic and germline CIDEB mutations are associated with protection from chronic liver diseases. The mechanistic basis and whether CIDEB suppression would be an effective therapy against fatty liver disease remain unclear. Methods21 CIDEB somatic mutations were introduced into cells to assess functionality. In vivo screening was used to trace Cideb mutant clones in mice fed normal chow, western (WD), and choline-deficient, L-amino acid-defined, high-fat (CDA-HFD) diets. Constitutive and conditional Cideb knockout mice were generated to study Cideb in liver disease. Isotope tracing was used to evaluate fatty acid oxidation and de novo lipogenesis. Transcriptomics, lipidomics, and metabolic analyses were utilized to explore molecular mechanisms. Double knockout models (Cideb/Atgl and Cideb/Ppara) tested mechanisms underlying Cideb loss. ResultsMost CIDEB mutations showed that they impair function, and lineage-tracing showed that loss-of-function clones were positively selected with some, but not all fatty liver inducing diets. Cideb KO mice were protected from WD, CDA-HFD, and alcohol diets, but had the greatest impact on CDA-HFD induced liver disease. Hepatocyte-specific Cideb deletion could ameliorate disease after MASLD establishment, modeling the impact of therapeutic siRNAs. Cideb loss protected livers via increased {beta}-oxidation, specifically through ATGL and PPARa activation. ConclusionsCideb deletion is more protective in some types of fatty liver disease. {beta}-oxidation is an important component of the Cideb protective mechanism. CIDEB inhibition represents a promising approach, and somatic mutations in CIDEB might predict the patient populations that might benefit the most.

physiology↗

Liver cancer initiation is dependent on metabolic zonation but decoupled from premalignant clonal expansion

The origin of cancer is poorly understood because cells that obtain truncal mutations are rarely fate mapped in their native environments. A defining feature of the liver is zonation, or the compartmentalization of metabolic functions in hepatocytes located in distinct regions of the lobule 1. However, it is unknown if cancers develop in some zones but not others, and if there are metabolic determinants of cancer risk that track with cellular position. To study cancer initiation, we examined the effect of activating mutations in Ctnnb1 and loss of function mutations in Arid2, two of the most commonly co-mutated genes in hepatocellular carcinoma (HCC) 2. We exploited glutamine synthetase (GS) as a faithful fate mapping marker of Ctnnb1 mutant hepatocytes. By introducing mutations in distinct zones in a mosaic fashion, we showed that position and metabolic context regulate clone expansion. Mutant clones were maintained in zone 1 but largely outcompeted in zone 3. Paradoxically, clonal maintenance was anti-correlated with cancer initiation, as zone 3 mutant livers showed increased tumorigenesis. To define mechanisms, we individually deleted eleven zone specific genes in HCC mouse models, revealing that Gstm2 and Gstm3 were required for efficient HCC initiation in zone 3. These data indicate that liver cancer initiation is dependent on zonation but independent of clonal expansion.

cancer biology↗

Positive selection of somatically mutated clones identifies adaptive pathways in metabolic liver disease

Somatic mutations in non-malignant tissues accumulate with age and insult, but whether these mutations are adaptive on the cellular or organismal levels is unclear. To interrogate mutations found in human metabolic disease, we performed lineage tracing in mice harboring somatic mosaicism subjected to non-alcoholic steatohepatitis (NASH). Proof-of-concept studies with mosaic loss of Mboat7, a membrane lipid acyltransferase, showed that increased steatosis accelerated clonal disappearance. Next, we induced pooled mosaicism in 63 known NASH genes, allowing us to trace mutant clones side-by-side. This in vivo tracing platform, which we coined MOSAICS, selected for mutations that ameliorate lipotoxicity, including mutant genes identified in human NASH. To prioritize new genes, additional screening of 472 candidates identified 23 somatic perturbations that promoted clonal expansion. In validation studies, liver-wide deletion of Bcl6, Tbx3, or Smyd2 resulted in protection against NASH. Selection for clonal fitness in mouse and human livers identifies pathways that regulate metabolic disease. HighlightsO_LIMosaic Mboat7 mutations that increase lipotoxicity lead to clonal disappearance in NASH. C_LIO_LIIn vivo screening can identify genes that alter hepatocyte fitness in NASH. C_LIO_LIMosaic Gpam mutations are positively selected due to reduced lipogenesis. C_LIO_LIIn vivo screening of transcription factors and epifactors identified new therapeutic targets in NASH. C_LI

cell biology↗

mRNAid, an Open-Source Platform for Therapeutic mRNA Design and Optimization Strategies

Recent COVID-19 vaccines unleashed the potential of mRNA-based therapeutics. mRNA optimization is indispensable for reducing immunogenicity, ensuring stability, and maximizing protein output. We present mRNAid, an experimentally validated software for mRNA optimization and visualization that generates mRNA sequences with comparable if not superior characteristics to commercially optimized sequences. To encompass all aspects of mRNA design, we also interrogated the impact of uridine content, nucleoside analogs and UTRs on expression and immunogenicity.

bioinformatics↗

Targeted degradation of PCNA outperforms stoichiometric inhibition to result in programed cell death

Targeted protein degradation has emerged as a powerful technology - both as a biological tool and for broadening the therapeutic proteome. As tools to probe this approach on historically intractable targets, we have previously advanced biodegraders -- targeted degradation fusion constructs composed of mini-proteins/peptides linked to modified E3 ligase receptors. Herein, we gain deeper insights into the utility and potential of biodegraders, through a detailed study on Con1-SPOP, a biodegrader which rapidly degrades the potential cancer target, proliferating cell nuclear antigen (PCNA). In a variety of settings, the active biodegrader (Con1-SPOP) proved pharmacologically superior to its stoichiometric (non-degrading) inhibitor equivalent (Con1-SPOPmut). Specifically, in addition to more potent anti-proliferative effects in both 2D cell culture and 3D spheroids, PCNA degradation uniquely induced DNA damage, cell apoptosis and necrosis. Global proteomic profiling of a stable cell-line expressing Con1-SPOP under doxycycline (Dox) induction revealed that impaired mitotic division and mitochondria dysfunction is a direct consequence of PCNA degradation, effects not seen with the stoichiometric inhibitor protein. To evaluate the therapeutic potential of biodegraders, we showed that Dox-induced Con1-SPOP achieved complete tumor-growth inhibition in a xenograft model. To explore application of biodegraders as a novel therapeutic modality, modified mRNA encoding Con1-SPOP was synthesized and encapsulated into lipid nanoparticles (LNPs). The approach successfully delivered mRNA in vitro to deplete endogenous PCNA within hours of application and with nanomolar potency. Overall, our results demonstrate the utility of biodegraders as biological tools and highlight target-degradation as a more efficacious approach versus stoichiometric inhibition. Finally, once in vivo delivery and expression are optimized, biodegraders may be leveraged as an exciting therapeutic modality.

cell biology↗

Discovery of cell active macrocyclic peptides with on-target inhibition of KRAS signaling

RAS is the most commonly mutated oncogene in human cancers and RAS-driven tumors are amongst the most difficult to treat. Historically, discovery of therapeutics targeting this protein has proven challenging due to a lack of deep hydrophobic pockets to which a small molecule might bind. The single such pocket available is normally occupied by GDP or GTP which have millimolar cellular concentrations and picomolar affinities for KRAS and hence is challenging to target. The recent FDA approval of sotorasib, a covalent modifier of the KRASG12C mutant protein, has clinically validated KRAS as an oncology target. However, traditional challenges remain for targeting the more common KRAS mutations such as G12D and G12V. As an alternative approach, we investigated the superior binding capacity of macrocyclic peptides to identify KRAS inhibitory molecules. We focused on the recently reported disulfide-cyclized arginine-rich peptide KRpep-2d, discovered through phage display and previously independently confirmed by us as a bona fide KRAS binder. To mitigate intracellular disulfide reduction and loss of binding, we identified an alternate cyclization motif by inverting the configuration of Cys5 and linking it to Cys15 through a thioacetal bridge. The corresponding peptide bound KRAS through cis isomerization of the peptide bond between D-Cys5 and Pro6 as observed through x-ray crystallography. Prototypic molecules displayed measurable cellular inhibition of RAS signaling without membrane lysis and counter-screen off-target activity. An analogue containing azido-lysine confirmed the cell penetrant nature of this molecule using our recently reported NanoClick assay. To improve cellular activity, we sought to improve proteolytic stability. Structure-activity relationship studies identified key scaffold residues critical for binding and revealed that replacement of N- and C-terminal arginine residues with D-arginines and introduction of an -methyl moiety at Ser10 resulted in a molecule with improved proteolytic stability as indicated by its persistence in whole cell homogenate. The resulting peptide MP-3995 had improved and sustained cell-based efficacy. On-target activity was validated through confirmation of target engagement, lack of signaling in irrelevant pathways, and use of non-binding control peptides. Mechanism of action studies suggested that peptide binding to both GDP- and GTP-states of KRAS may contribute to cellular activity. Although validated as bona fide and on-target inhibitors of cell based KRAS signaling, this series is unlikely to advance to the clinic in its current form due to its arginine-dependent cell entry mechanism. Indeed, we showed a strong correlation between net positive charge and histamine release in an ex vivo assay making this series challenging to study in vivo. Nonetheless, these molecules provide valuable templates for further medicinal chemistry efforts aimed at leveraging this unique inhibitory binding site on KRAS. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=118 SRC="FIGDIR/small/459913v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@17f4764org.highwire.dtl.DTLVardef@12818daorg.highwire.dtl.DTLVardef@177bdf0org.highwire.dtl.DTLVardef@57046c_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

Ablating Ku70 phosphorylation results in defective DNA damage repair and spontaneous induction of hepatocellular carcinoma

Multiple pathways mediate the repair of DNA double-strand break (DSB), with numerous mechanisms responsible for driving choice between the pathways. Previously, we reported that phosphorylation of the non-homologous end joining (NHEJ) factor, Ku70, is required for the dissociation of the Ku heterodimer from DNA ends to allow DSB repair via homologous recombination (HR). A knock-in mouse, in which phosphorylation is ablated in the three conserved sites of Ku70 (Ku703A/3A), was generated in order to test the hypothesis that Ku70 phosphorylation is required for initiation of HR and that blocking this process results in enhanced genomic instability and tumorigenesis. Here, we show that Ku703A/3A mice develop spontaneous and have accelerated chemical-induced hepatocellular carcinoma (HCC) compared to wild-type (Ku70+/+) littermates. The HCC tumors from the Ku703A/3A mice have increased {gamma}H2AX and 8-oxo-G staining, suggesting DNA repair is decreased in these mice. Spontaneous transformed cell lines from Ku703A/3A mice are more radiosensitive, have a significant decrease in DNA end resection, and are more sensitive to the DNA cross-linking agent mitomycin C compared to cells from Ku70+/+ littermates. Collectively, these findings demonstrate that phosphorylation-mediated dissociation of Ku heterodimer from DNA ends is required for efficient DNA damage repair and disruption of this process results in genomic instability and accelerated development of HCC.

cancer biology↗

STUB1 is an intracellular checkpoint for interferon gamma sensing

Immune checkpoint blockade (ICB) leads to durable and complete tumour regression in some patients but in others gives temporary, partial or no response. Accordingly, significant efforts are underway to identify tumour-intrinsic mechanisms underlying ICB resistance. Results from a published CRISPR screen in a mouse model suggested that targeting STUB1, an E3 ligase involved in protein homeostasis, may overcome ICB resistance but the molecular basis of this effect remains unclear. Herein, we report an under-appreciated role of STUB1 to dampen the interferon gamma (IFN{gamma}) response. Genetic deletion of STUB1 increased IFNGR1 abundance on the cell surface and thus enhanced the downstream IFN{gamma} response as showed by multiple approaches including Western blotting, flow cytometry, qPCR, phospho-STAT1 assay, immunopeptidomics, proteomics, and gene expression profiling. Human prostate and breast cancer cells with STUB1 deletion were also susceptible to cytokine-induced growth inhibition. Furthermore, blockade of STUB1 protein function recapitulated the STUB1-null phenotypes. Despite these encouraging in vitro data and positive implications from clinical datasets, we did not observe in vivo benefits of inactivating Stub1 in mouse syngeneic tumour models - with or without combination with anti-PD-1 therapy. However, our findings elucidate STUB1 as a barrier to IFN{gamma} sensing, prompting further investigations to assess if broader inactivation of human STUB1 in both tumors and immune cells could overcome ICB resistance.

cancer biology↗

bioPROTACs establish RAS as a degradable target and provide novel RAS biology insights

ABSTRACTMutations to RAS proteins (H-, N-, and K-RAS) are amongst the most common oncogenic drivers and tumors harboring these lesions are some of the most difficult to treat. Although the recently discovered covalent small molecules against the KRASG12C mutant have shown promising efficacy against lung cancers, traditional barriers remain for drugging the more prevalent KRASG12D and KRASG12V mutants. Targeted degradation has emerged as an attractive alternative approach but for KRAS, identification of the required high-affinity ligands continues to be a challenge. Another significant hurdle is the discovery of a hybrid molecule that appends an E3 ligase-recruiting moiety in a manner that satisfies the precise geometries required for productive polyubiquitin transfer while maintaining favorable drug-like properties. As a tool to gain insights into the advantages and feasibility of KRAS targeted-degradation, we applied the bioPROTAC approach. This workflow centers on the intracellular expression of a chimeric protein consisting of a high-affinity target-binding domain fused to an engineered E3 ligase adapter. We generated a series of anti-RAS bioPROTACs that span different RAS isoform/nucleotide-state specificities and leverage different E3 ligases. Overall, our results provide definitive evidence for the degradability of RAS proteins. We further elucidate the functional consequences of RAS degradation, the susceptibility and degradation kinetics of various mutant KRAS, and the prevalence of different nucleotide-states in WT and mutant KRAS. Finally, if delivery challenges can be addressed, anti-RAS bioPROTACs will be exciting candidates for clinical development.Competing Interest StatementThe authors have declared no competing interest.View Full Text

cancer biology↗

Phase variation in Mycobacterium tuberculosis glpK produces transiently heritable drug tolerance

The length and complexity of tuberculosis (TB) therapy, as well as the propensity of Mycobacterium tuberculosis to develop drug resistance, are major barriers to global TB control efforts. M. tuberculosis is known to have the ability to enter into a drug-tolerant state, which may explain many of these impediments to TB treatment. We have identified a novel mechanism of genetically encoded but rapidly reversible drug-tolerance in M. tuberculosis caused by transient frameshift mutations in a homopolymeric tract (HT) of seven cytosines (7C) in the glpK gene. Inactivating frameshift mutations associated with the 7C HT in glpK produce small colonies that exhibit heritable multi-drug increases in minimal inhibitory concentrations and decreases in drug-dependent killing; however, reversion back to a fully drug-susceptible large-colony phenotype occurs rapidly through the introduction of additional insertions or deletions in the same glpK HT region. These reversible frameshift mutations in the 7C HT of M. tuberculosis glpK occur in clinical isolates, accumulate in M. tuberculosis infected mice with further accumulation during drug treatment, and exhibit a reversible transcriptional profile including induction of dosR and sigH and repression of kstR regulons, similar to that observed in other in vitro models of M. tuberculosis tolerance. These results suggest that GlpK phase variation may contribute to drug-tolerance, treatment failure and relapse in human TB. Drugs effective against phase-variant M. tuberculosis may hasten TB treatment and improve cure rates.\n\nSIGNIFICANCEThe ability of M. tuberculosis to survive during prolonged treatment has been attributed to either transient stress responses or fixed heritable drug-resistance producing mutations. We show that phase-variation in the M. tuberculosis glpK gene represents a third type of resistance mechanism. The ability of these glpK mutants to grow slowly and then rapidly revert suggests that these transiently-heritable changes may also explain how a hidden population of drug-tolerant bacteria develops during TB treatment. As a genetically trackable cause of drug-tolerance, M. tuberculosis glpK mutants provides a unique opportunity to study these phenomena at a cellular and mechanistic level. These mutants could also be used for developing drugs that target tolerant populations, leading to more rapid and effective TB treatments.

microbiology↗

Pyrazinamide triggers degradation of its target aspartate decarboxylase

The introduction of pyrazinamide (PZA) in the tuberculosis drug regimen shortened treatment from 12 to 6 months 1. PZA is a prodrug that is activated by a Mycobacterium tuberculosis (Mtb) amidase to release its bioactive component pyrazinoic acid (POA) 2. Aspartate decarboxylase PanD, a proenzyme activated by autocatalytic cleavage (Supplementary Fig. 1A, 3) and required for Coenzyme A (CoA) biosynthesis, emerged as a target of POA 4-7. In vitro and in vivo screening to isolate spontaneous POA-resistant Mtb mutants identified missense mutations in either panD or the unfoldase clpC1, encoding a component of the caseinolytic protease ClpC1-ClpP 4,6-9. Overexpression and binding studies of PanD or ClpC1 pointed to PanD as the direct target of POA whereas clpC1 mutations appeared to indirectly cause resistance 4,5,7,9,10. Indeed, supplementing growth media with CoA precursors downstream of the PanD catalyzed step conferred POA resistance 4,7,11. Metabolomic analyses and biophysical studies using recombinant proteins confirmed targeting of PanD by POA 5. However, the exact molecular mechanism of PanD inhibition by POA remained unknown. While most drugs act by inhibiting protein function upon target binding, we show here that POA is not a bona fide enzyme inhibitor. Rather, POA binding to PanD triggers degradation of the protein by ClpC1-ClpP. Thus, the old tuberculosis drug PZA promotes degradation of its target. While novel for an antibacterial, drug-induced target degradation has recently emerged as a strategy in drug discovery across disease indications. Our findings provide the basis for the rational discovery of next generation PZA.

microbiology↗