mBio最新文献

{"title":"Calprotectin-mediated survival of <i>Staphylococcus aureus</i> in coculture with <i>Pseudomonas aeruginosa</i> occurs without nutrient metal sequestration.","authors":"Wei H Lee, Emily M Zygiel, Celis H Lee, Amanda G Oglesby, Elizabeth M Nolan","doi":"10.1128/mbio.03846-24","DOIUrl":"https://doi.org/10.1128/mbio.03846-24","url":null,"abstract":"<p><p><i>Pseudomonas aeruginosa</i> and <i>Staphylococcus aureus</i> are bacterial pathogens of major clinical concern that cause polymicrobial infections in diverse patient populations. Human calprotectin (CP; S100A8/S100A9 heterooligomer, MRP8/MRP14 heterooligomer) is a host-defense protein that contributes to nutritional immunity by sequestering multiple nutrient metal ions including Mn(II), Fe(II), and Zn(II). Here, we examine the consequences of metal availability and CP treatment on cocultures of <i>P. aeruginosa</i> and <i>S. aureus</i>. We report that CP elicits Fe-starvation responses in both <i>P. aeruginosa</i> and <i>S. aureus</i> in coculture, including the upregulation of genes involved in Fe uptake by both organisms. Moreover, analyses of pseudomonal metabolites in coculture supernatants further demonstrate Fe-starvation responses, showing that CP treatment leads to increased siderophore levels and reduced phenazine levels. Consistent with prior studies, growth under conditions of Fe depletion accelerated <i>P. aeruginosa</i> killing of <i>S. aureus</i> in coculture, but treatment with CP promoted <i>S. aureus</i> survival. Treatment with CP site variants lacking functional transition-metal-binding sites and metalated CP also enhanced <i>S. aureus</i> survival in coculture with <i>P. aeruginosa</i>, revealing that this consequence of CP treatment is independent of its canonical metal-sequestering function. Thus, the protective effects of CP treatment during coculture appear to override the observed Fe-starvation effects that make <i>P. aeruginosa</i> more virulent toward <i>S. aureus</i>. This work highlights an unappreciated facet of how CP contributes to host-pathogen and pathogen-pathogen interactions that are relevant to human infectious disease.</p><p><strong>Importance: </strong>The current working model that describes how the innate immune protein calprotectin (CP) protects the host against bacterial pathogens focuses on its capacity to sequester multiple essential metal nutrients in a process called nutritional immunity. Our study further explores this function by focusing on the effects of metal availability and CP treatment on the dynamics of <i>Pseudomonas aeruginosa</i> and <i>Staphylococcus aureus</i> grown in coculture. These two bacterial pathogens are of significant clinical concern and colocalize with CP at infection sites. This work reveals that CP modulates <i>P. aeruginosa/S. aureus</i> coculture dynamics in a manner that is independent of its ability to sequester nutrient metal ions. This surprising result is important because it demonstrates that CP has metal-independent function and thus contributes to the host-pathogen and pathogen-pathogen interactions in ways that are not accounted for in the current working model focused on metal sequestration.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":" ","pages":"e0384624"},"PeriodicalIF":5.1,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143730611","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Functional characterization of a novel protein-coding circular RNA, circRNA_1193, from the <i>mAAP</i> gene in silkworm and its role in antiviral defense against BmCPV.","authors":"Song Li, Zeen Shen, Hongchuan Zhao, Xialing Chen, Qunnan Qiu, Xinyu Tong, Min Zhu, Xing Zhang, Chengliang Gong, Xiaolong Hu","doi":"10.1128/mbio.00125-25","DOIUrl":"https://doi.org/10.1128/mbio.00125-25","url":null,"abstract":"<p><p>A novel circular RNA, circRNA_1193, which originates from the <i>membrane alanyl aminopeptidase-like</i> gene in silkworms, was explored for its potential function and regulatory mechanism. We validated the presence of circRNA_1193 in <i>Bombyx mori</i> cytoplasmic polyhedrosis virus (BmCPV)-infected silkworm ovary cell line (BmN) cells through a combination of reverse transcription polymerase chain reaction, Northern blotting, and <i>in situ</i> hybridization. CircRNA_1193 exhibited tissue-specific expression, being highly enriched in the midgut and Malpighian tubules, and displayed a specific response to BmCPV infection, but not to <i>Bombyx mori</i> nucleopolyhedrovirus or lipopolysaccharide. Functional analyses revealed that the overexpression of circRNA_1193 suppressed BmCPV replication, whereas its knockdown increased viral replication. Bioinformatic analyses revealed potential internal ribosome entry sites, m6A methylation sites, and open reading frames (ORFs) within circRNA_1193, suggesting its potential coding capacity. We confirmed the translation of the ORF by constructing a DsRed reporter vector and demonstrating DsRed expression in transfected cells. Furthermore, a mutation of the start codon within circRNA_1193 abolished its antiviral activity, highlighting the crucial role of the translated protein, which is 35 kDa and is designated as VSP35. Furthermore, our data suggest that the formation of circRNA_1193 relies on reverse complementary flanking sequences. These findings unveil a novel protein-coding circular RNA in silkworms that plays a critical role in antiviral defense.</p><p><strong>Importance: </strong>This study identified a novel circular RNA, circRNA_1193, in the silkworm <i>Bombyx mori</i>, and revealed its critical role in antiviral defense against <i>Bombyx mori</i> cytoplasmic polyhedrosis virus (BmCPV). We demonstrated that circRNA_1193 exhibits tissue-specific expression, is upregulated in response to BmCPV infection, and possesses antiviral activity. Importantly, we show that circRNA_1193 encodes the viral protein VSP35, which is essential for its antiviral function. These findings provide new insights into the complex regulatory mechanisms of circular RNAs in antiviral immunity and underscore the potential of circular RNAs as therapeutic targets in viral diseases. The identification of a protein-coding circular RNA with antiviral activity in <i>B. mori</i> has broader implications for understanding the evolution and diversity of host defense mechanisms against viruses.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":" ","pages":"e0012525"},"PeriodicalIF":5.1,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143730733","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Differential crosstalk between toxin-immunity protein homologs divides <i>Myxococcus</i> nonself siblings into close and distant social relatives.","authors":"Feng Wang, Jing Luo, Zheng Zhang, Ya Liu, Duo Hong Sheng, Li Zhuo, Yue-Zhong Li","doi":"10.1128/mbio.03902-24","DOIUrl":"https://doi.org/10.1128/mbio.03902-24","url":null,"abstract":"<p><p>Many bacteria discriminate self and nonself using toxins and their corresponding immunity proteins. The toxin-immunity systems often include homologs, potentially creating crosstalk with unknown influences on kin discrimination. In this study, we investigated the kinship controlled by four homologous toxin-immunity systems in the social bacterium <i>Myxococcus xanthus</i>. We determined that the four homologous systems each play an independent role in the discrimination of self and nonself. However, the immunity proteins inactivate not only the corresponding nuclease toxin proteins but also some non-corresponding toxin proteins, depending on their sequence and structural similarities. The nonself relatives controlled by toxin-immunity proteins with or without crosstalk exhibit differential co-growth and collaborative behaviors. We concluded that differential crosstalk between toxin-immunity protein homologs can divide bacterial nonself lineages into close and distant relatives displaying differential collaboration and antagonistic behaviors.IMPORTANCEThis study significantly contributes to our knowledge of kin selection and social behavior in bacteria. The interactions between four homologous toxin-immunity protein systems of <i>Myxococcus xanthus</i> were investigated, and evidence was obtained that these systems can distinguish between self and nonself cells within a species. Importantly, this study revealed that nonself lineages, which display varying degrees of genetic relatedness, can co-grow and collaborate in distinct patterns. This discovery implies that the differential crosstalk between homologous toxin-immunity proteins can mimic the degree of kinship; through this activity, bacteria can differentiate close and distant relatives. This novel insight into bacterial social dynamics and kin discrimination supports kin selection theory and enriches our knowledge on microbial interactions and evolutionary strategies. These findings have broad implications for microbial ecology, evolution, and the development of cooperation strategies.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":" ","pages":"e0390224"},"PeriodicalIF":5.1,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143730618","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Herpes simplex virus type 1 impairs mucosal-associated invariant T cells.","authors":"Lauren Stern, Zoe Emanuel, Renee Traves, Katherine Willis, Shivam K Purohit, Carolyn Samer, Jeffrey Y W Mak, David P Fairlie, David C Tscharke, Alexandra J Corbett, Allison Abendroth, Barry Slobedman","doi":"10.1128/mbio.03887-24","DOIUrl":"https://doi.org/10.1128/mbio.03887-24","url":null,"abstract":"<p><p>Herpes simplex virus type 1 (HSV-1) is a highly successful pathogen that infects mucosal sites and adopts an arsenal of strategies to manipulate host immunity. Mucosal-associated invariant T (MAIT) cells are abundant innate-like T lymphocytes that recognize bacterial and fungal-derived vitamin B-related metabolites presented by major histocompatibility complex class I-related protein 1 (MR1). MAIT cells can also be activated in an MR1-independent manner via cytokine stimulation, predominantly by IL-12 and IL-18. MAIT cell alterations have been identified as being associated with a number of viral infections, but direct interactions between viruses and MAIT cells are poorly understood. It is unknown whether HSV-1 can infect MAIT cells and modulate their functions. Here, we show that HSV-1 can infect primary human MAIT cells, including CD4^±/CD8^± and CD56^± MAIT cell subpopulations. Furthermore, HSV-1 infection profoundly inhibits the functional capacity of MAIT cells to respond to T cell receptor (TCR)-dependent stimulation by the MAIT cell activating ligand 5-(2-oxopropylideneamino)-6-D-ribitylaminouracil (5-OP-RU) and to cytokine stimulation by IL-12/IL-18. HSV-1-infected MAIT cells display reduced cytotoxic potential, diminished synthesis of effector cytokines, and decreased expression of key cytokine receptors including IL-18R. In addition, MAIT cells exposed to HSV-1-infected fibroblasts but which remained uninfected (viral GFP-negative) also exhibit a suppressed effector response to TCR-dependent stimulation. The functional suppression of HSV-1-exposed MAIT cells was not mediated by a soluble factor within the supernatant, suggesting direct contact of MAIT cells with HSV-1-infected fibroblasts is required. Overall, this study reveals that HSV-1 can infect MAIT cells and substantially impair MAIT cell effector functions.</p><p><strong>Importance: </strong>Mucosal-associated invariant T cells (MAIT cells) are \"unconventional\" immune cells that are becoming increasingly appreciated to play important roles in a variety of viral infections. Herpes simplex virus (HSV) causes significant human disease and is a master manipulator of multiple immune functions, but how this virus may control MAIT cells is poorly understood. We discovered that HSV can infect human MAIT cells and impair their functional capacity and also show that MAIT cells exposed to HSV, but which do not show evidence of infection, are similarly impaired. This study therefore identifies an additional immunomodulatory function of HSV.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":" ","pages":"e0388724"},"PeriodicalIF":5.1,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143710606","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Discovery of novel antifungal drugs via screening repurposing libraries against <i>Coccidioides posadasii</i> spherule initials.","authors":"Sarah Saeger, Kathryn West-Jeppson, Yu-Rou Liao, Althea Campuzano, Jieh-Juen Yu, Jose Lopez-Ribot, Chiung-Yu Hung","doi":"10.1128/mbio.00205-25","DOIUrl":"https://doi.org/10.1128/mbio.00205-25","url":null,"abstract":"<p><p>Coccidioidomycosis or valley fever is a treatment-limited fungal infection endemic to the alkaline deserts of North and South America for which two classes of antifungals are typically used: the polyenes and the triazoles. In light of the limited usefulness of the echinocandins and a growing trend of azole resistance, it is essential that we identify novel antifungals. In this study, we have developed and optimized a screening methodology for identifying potential antifungals effective against <i>Coccidioides</i> spherule initials using a metabolic assay, used it to screen four diverse drug libraries with limited drug overlap, and established safety and efficacy data for a majority of the compounds, including the Broad Repurposing Hub, Prestwick Chemicals 1520, Selleck L8200 Anti-parasitic, and MedChemExpress CNS Penetrants libraries. Hits were defined as compounds with strong metabolic inhibition (≥70%), which were significantly different compared to the median plate readout (B-scores ≤ -3). We identified 30 promising hits and found 12 compounds exhibiting half-maximal inhibitory concentrations below 6 µM. Among these, oxethazaine, niclosamide ethanolamine, 10058-F4, niclosamide (NIC), and pentamidine isethionate showed synergy with amphotericin B, suggesting their potential use in combination therapy. Further assessment of lead compounds' effects on spherules was conducted by image flow cytometry. Additionally, we explored the potential to use an attenuated, Biosafety Level 2 containment mutant, <i>C. posadasii</i> ∆<i>cts2</i>/∆<i>ard1</i>/∆<i>cts3</i> (∆T), as a surrogate model for drug screening. Overall, our findings provide a foundation for future research focused on screening and developing novel coccidioidomycosis treatments.IMPORTANCEThe antifungal treatment arsenal is especially limited against <i>Coccidioides</i>. Due to toxicity concerns, amphotericin B is generally reserved for triazole-recalcitrant infections. Recent laboratory susceptibility tests show an increase in fluconazole resistance, highlighting a need for new treatments. We have developed a large-scale metabolic screening assay under Biosafety Level 3 containment to identify existing drugs with novel activity against <i>Coccidioides</i> spherules. This drug-repurposing approach represents a convenient and cost-effective strategy to increase the available antifungals effective against these infections.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":" ","pages":"e0020525"},"PeriodicalIF":5.1,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143710596","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Neutralization and spike stability of JN.1-derived LB.1, KP.2.3, KP.3, and KP.3.1.1 subvariants.","authors":"Pei Li, Julia N Faraone, Cheng Chih Hsu, Michelle Chamblee, Yajie Liu, Yi-Min Zheng, Yan Xu, Claire Carlin, Jeffrey C Horowitz, Rama K Mallampalli, Linda J Saif, Eugene M Oltz, Daniel Jones, Jianrong Li, Richard J Gumina, Joseph S Bednash, Kai Xu, Shan-Lu Liu","doi":"10.1128/mbio.00464-25","DOIUrl":"10.1128/mbio.00464-25","url":null,"abstract":"<p><p>During the summer of 2024, coronavirus disease 2019 (COVID-19) cases surged globally, driven by variants derived from JN.1 subvariants of severe acute respiratory syndrome coronavirus 2 that feature new mutations, particularly in the N-terminal domain (NTD) of the spike protein. In this study, we report on the neutralizing antibody (nAb) escape, infectivity, fusion, and spike stability of these subvariants-LB.1, KP.2.3, KP.3, and KP.3.1.1. Our findings demonstrate that all of these subvariants are highly evasive of nAbs elicited by the bivalent mRNA vaccine, the XBB.1.5 monovalent mumps virus-based vaccine, or from infections during the BA.2.86/JN.1 wave. This reduction in nAb titers is primarily driven by a single serine deletion (DelS31) in the NTD of the spike, leading to a distinct antigenic profile compared to the parental JN.1 and other variants. We also found that the DelS31 mutation decreases pseudovirus infectivity in CaLu-3 cells, which correlates with impaired cell-cell fusion. Additionally, the spike protein of DelS31 variants appears more conformationally stable, as indicated by reduced S1 shedding both with and without stimulation by soluble ACE2 and increased resistance to elevated temperatures. Molecular modeling suggests that DelS31 enhances the NTD-receptor-binding domain (RBD) interaction, favoring the RBD down conformation and reducing accessibility to ACE2 and specific nAbs. Moreover, DelS31 introduces an N-linked glycan at N30, shielding the NTD from antibody recognition. These findings underscore the role of NTD mutations in immune evasion, spike stability, and viral infectivity, highlighting the need to consider DelS31-containing antigens in updated COVID-19 vaccines.IMPORTANCEThe emergence of novel severe acute respiratory syndrome coronavirus 2 variants continues to pose challenges for global public health, particularly in the context of immune evasion and viral stability. This study identifies a key N-terminal domain (NTD) mutation, DelS31, in JN.1-derived subvariants that enhances neutralizing antibody escape while reducing infectivity and cell-cell fusion. The DelS31 mutation stabilizes the spike protein conformation, limits S1 shedding, and increases thermal resistance, which possibly contribute to prolonged viral persistence. Structural analyses reveal that DelS31 enhances NTD-receptor-binding domain interactions by introducing glycan shielding, thus decreasing antibody and ACE2 accessibility. These findings emphasize the critical role of NTD mutations in shaping viral evolution and immune evasion, underscoring the urgent need for updated coronavirus disease 2019 vaccines that account for these adaptive changes.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":" ","pages":"e0046425"},"PeriodicalIF":5.1,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143710607","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"RIG-I and cGAS mediate antimicrobial and inflammatory responses of primary osteoblasts and osteoclasts to <i>Staphylococcus aureus</i>.","authors":"Erin L Mills, Samantha R Suptela, Mary-Kate Key, Ian Marriott, M Brittany Johnson","doi":"10.1128/mbio.03971-24","DOIUrl":"https://doi.org/10.1128/mbio.03971-24","url":null,"abstract":"<p><p><i>Staphylococcus aureus</i> is the primary causative agent of osteomyelitis, and it is now apparent that osteoblasts and osteoclasts play a significant role in the pathogenesis of such infections. Their responses can either be protective or exacerbate inflammatory bone loss and are mediated by the recognition of microbial motifs by various pattern recognition receptors. We have recently reported that osteoblasts can respond to <i>S. aureus</i> challenge with the production of the type I interferon, interferon-beta, which can reduce the number of viable bacteria harbored within infected cells. In the present study, we demonstrate that <i>S. aureus</i> viability and internalization are necessary for maximal inflammatory cytokine and type I interferon responses of primary bone cells to this pathogen. Importantly, we show that primary murine and human bone cells constitutively express the cytosolic nucleic acid sensors, retinoic acid inducible gene I (RIG-I) and cyclic GMP-AMP synthase (cGAS), and demonstrate that such expression is markedly upregulated following <i>S. aureus</i> infection. The functional status of RIG-I and cGAS in osteoblasts and osteoclasts was confirmed by showing that specific ligands for each can also elevate their expression and induce cytokine responses. We have verified the specificity of such responses using siRNA knockdown or pharmacological inhibition and used these approaches to demonstrate that both sensors play a pivotal role in bone cell responses to infection with clinically relevant strains of <i>S. aureus</i>. Finally, we have begun to establish the biological significance of RIG-I- and cGAS-mediated bone cell responses with the demonstration that their attenuation increases <i>S. aureus</i> burden in infected cells, suggesting a potentially protective role for these sensors in osteomyelitis.IMPORTANCEStaphylococcal osteomyelitis is a severe infection that is often recalcitrant to current treatment strategies. We and others have demonstrated that resident bone cells are not merely passive victims but can respond to bacteria with the production of an array of immune mediators, including type I interferons, that could serve to limit such infections. Here, we demonstrate the functional expression of two cytosolic nucleic acid sensors, retinoic acid inducible gene I and cyclic GMP-AMP synthase, in primary murine and human osteoblasts and murine osteoclasts. We show that these pattern recognition receptors mediate potentially protective bone cell type I interferon responses to <i>Staphylococcus aureus</i> infection.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":" ","pages":"e0397124"},"PeriodicalIF":5.1,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143710608","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evidence of a role for the F1 capsule of <i>Yersinia pestis</i> in enhancing transmission from mammals to fleas in a mouse model of bubonic plague.","authors":"Christopher F Bosio, Clayton O Jarrett, B Joseph Hinnebusch","doi":"10.1128/mbio.00301-25","DOIUrl":"10.1128/mbio.00301-25","url":null,"abstract":"<p><p>The F1 protein capsule of <i>Yersinia pestis</i> is encoded by the <i>caf</i> operon on the 100 kb plasmid pFra and is produced at high levels in the mammalian host. Although the F1 capsule is not an essential virulence factor in many mammals, <i>Y. pestis</i> isolates lacking the <i>caf</i> operon are very rare in nature, indicating an essential biological role. Here, we show that F1-negative Δ<i>caf</i> mutants of <i>Y. pestis</i> are virulent in a mouse model but with a longer time to terminal disease. Bacterial loads in the spleen at the terminal stage of plague were not significantly different from the wild type. However, the level of bacteremia reached by the Δ<i>caf</i> mutants was often significantly lower than the wild type. Fleas that fed on moribund mice infected with the Δ<i>caf</i> mutants ingested the expected number of bacteria, but most mice had levels of bacteremia too low to support the development of a transmissible infection in the flea. A complemented Δ<i>caf</i> mutant restored wildtype levels of bacteremia and median time to death. F1-negative <i>Y. pestis</i> have a more pronounced autoaggregative phenotype, both <i>in vitro</i> and <i>in vivo</i>, which likely leads to a higher degree of sequestration in the spleen and other tissues. Therefore, an important biological role of the F1 capsule may be to enable <i>Y. pestis</i> to achieve bacteremia levels high enough to efficiently infect fleas, thereby enhancing stable flea-borne transmission cycles of <i>Y. pestis</i>.IMPORTANCEArthropod-borne pathogens face two fundamental challenges in completing their life cycle-they must produce a transmissible infection in both their mammalian and arthropod hosts. In order to effectively infect its flea vector, <i>Yersinia pestis</i>, the bacterial agent of plague, must generate a high-density bacteremia in the mammalian hosts that the fleas feed upon. In this study, we found that the F1 protein capsule of <i>Y. pestis</i> enhances the production of high bacteremia at the terminal stage of plague in a mouse model, thereby promoting successful mammal-to-flea transmission. Acquisition of the plasmid that encodes the F1 capsule occurred early in the evolutionary divergence of <i>Y. pestis</i> from <i>Yersinia pseudotuberculosis</i> and was likely to have been a key step in the transition to a flea-borne lifestyle.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":" ","pages":"e0030125"},"PeriodicalIF":5.1,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143710597","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Complex roles for proliferating cell nuclear antigen in restricting human cytomegalovirus replication.","authors":"Pierce Longmire, Olivia Daigle, Sebastian Zeltzer, Matias Lee, Marek Svoboda, Marco Padilla-Rodriguez, Carly Bobak, Giovanni Bosco, Felicia Goodrum","doi":"10.1128/mbio.00450-25","DOIUrl":"10.1128/mbio.00450-25","url":null,"abstract":"<p><p>DNA viruses at once elicit and commandeer host pathways, including DNA repair pathways, for virus replication. Despite encoding its own DNA polymerase and processivity factor, human cytomegalovirus (HCMV) recruits the cellular processivity factor, proliferating cell nuclear antigen (PCNA) and specialized host DNA polymerases involved in translesion synthesis (TLS) to replication compartments (RCs) where viral DNA (vDNA) is synthesized. While the recruitment of TLS polymerases is important for viral genome stability, the role of PCNA is poorly understood. PCNA function in DNA repair is regulated by monoubiquitination (mUb) or SUMOylation of PCNA at lysine 164 (K164). We find that mUb-PCNA increases over the course of infection, and modification of K164 is required for PCNA-mediated restriction of virus replication. mUb-PCNA plays important known roles in recruiting TLS polymerases to DNA, which we have shown are important for viral genome integrity and diversity, represented by structural variants and single nucleotide variants (SNVs), respectively. We find that PCNA drives SNVs on vDNA similar to Y-family TLS polymerases, but this did not require modification at K164. Unlike TLS polymerases, depeletion of PCNA did not result in large-scale rearrangements on vDNA. These striking results suggest separable PCNA-dependent and -independent functions of TLS polymerases on vDNA. By extension, these results imply roles for TLS polymerase beyond their canonical function in TLS in host biology. These findings highlight PCNA as a complex restriction factor for HCMV infection, likely with multiple distinct roles, and provide new insights into the PCNA-mediated regulation of DNA synthesis and repair in viral infection.IMPORTANCEGenome synthesis is a critical step of virus life cycles and a major target of antiviral drugs. Human cytomegalovirus (HCMV), like other herpesviruses, encodes machinery sufficient for viral DNA synthesis and relies on host factors for efficient replication. We have shown that host DNA repair factors play important roles in HCMV replication, but our understanding of this is incomplete. Building on previous findings that specialized host DNA polymerases contribute to HCMV genome integrity and diversity, we sought to determine the importance of proliferating cell nuclear antigen (PCNA), the central polymerase regulator. PCNA is associated with nascent viral DNA and restricts HCMV replication. While PCNA is dispensable for genome integrity, it contributes to genome diversity. Our findings suggest that host polymerases function on viral genomes by separable PCNA-dependent and -independent mechanisms. Through revealing complex roles for PCNA in HCMV replication, this study expands the repertoire of host DNA synthesis and repair proteins hijacked by this ubiquitous herpesvirus.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":" ","pages":"e0045025"},"PeriodicalIF":5.1,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143699566","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cellular SLC35B4 promotes internalization during influenza A virus entry.","authors":"Guangwen Wang, Li Jiang, Ya Yan, Fandi Kong, Qibing Li, Jie Zhang, Shuangshuang Hou, Bo Wang, Xiurong Wang, Huihui Kong, Guohua Deng, Jianzhong Shi, Guobin Tian, Xianying Zeng, Hualan Chen, Chengjun Li","doi":"10.1128/mbio.00194-25","DOIUrl":"https://doi.org/10.1128/mbio.00194-25","url":null,"abstract":"<p><p>SLC35B4, a nucleotide sugar transporter that mediates the transport of UDP-GlcNAc and UDP-xylose, was found to be required for the replication of influenza A virus (IAV) of the H5N1 subtype in our genome-wide siRNA library screen. We found that defective IAV replication in SLC35B4-deficient A549 cells was independent of virus strain specificity, and the virulence of IAV in Slc35b4 knockdown mice was also decreased. By examining the individual stages of the IAV replication cycle, we discovered that the amount of internalized IAV was significantly reduced in SLC35B4-knockout A549 cells. Mechanistically, SLC35B4 facilitated IAV replication by transporting UDP-xylose, which attaches to the serine residue of heparan sulfate proteoglycans (HSPGs) in the heparan sulfate (HS) biosynthesis pathway. Knockdown of associated host factors (i.e., XYLT2, B4GALT7, EXT1, and EXT2) in the HS biosynthesis pathway also impaired IAV replication. Furthermore, we revealed that AGRN, a unique HSPG family member, was important for the endocytosis of IAV in A549 cells. Moreover, we found that the homeostasis of the AGRN protein was regulated by HS modification mediated by the initial UDP-xylose transporter SLC35B4, thereby affecting the expression level of endocytic adapter AP2B1 to influence IAV internalization. Collectively, these findings establish that SLC35B4 is an important regulator of IAV replication and uncover the underlying mechanisms by which SLC35B4 employs UDP-xylose transport activity to promote IAV internalization.IMPORTANCEThe entry process of IAV represents a favorable target for drug development. In this study, we identified SLC35B4 as an important host factor for the efficient replication of different subtypes of IAV <i>in vitro</i> and for the virulence of IAV in mice. We revealed that SLC35B4 employed its UDP-xylose transport activity to promote the HS biosynthesis pathway, thereby assisting IAV internalization into target cells in the early stage of viral infection. Consistently, several downstream factors in the HS biosynthesis pathway, i.e., XYLT2, B4GALT7, EXT1, and EXT2, as well as a specific HSPG member AGRN were also important for the replication of IAV. Furthermore, the UDP-xylose-transporting activity of SLC35B4 was involved in the regulation of the homeostasis of the AGRN protein by HS modification, which influenced virus internalization by affecting the expression levels of AP2B1. Together, the identification of the SLC35B4-XYLT2-B4GALT7-EXT1-EXT2-AGRN-AP2B1 axis may shed light on the development of potential anti-IAV therapeutics.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":" ","pages":"e0019425"},"PeriodicalIF":5.1,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143700965","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}