RpoS activates Salmonella Typhi biofilms and drives persistence in a Zebrafish model.

The development of strategies for targeting the asymptomatic carriage of Salmonella Typhi in chronic typhoid patients has suffered owing to our basic lack of understanding of the molecular mechanisms that enable the formation of S. Typhi biofilms. Traditionally, studies have relied on cholesterol-attached biofilms formed by a closely related serovar, Typhimurium, to mimic multicellular Typhi communities formed on human gallstones. In long-term infections, S. Typhi adopts the biofilm lifestyle to persist in vivo and survive in the carrier state, ultimately leading to the spread of infections via the fecal-oral route of transmission. In the present work, we studied S. Typhi biofilms directly, applied targeted as well as genome-wide genetic approaches to uncover unique biofilm components that do not conform to the CsgD-dependent pathway as established in S. Typhimurium. We adopted a genome-wide Tn5 mutation screen in S. Typhi in gallstone-mimicking conditions and generated New Generation Sequencing libraries based on the ClickSeq technology to identify the key regulators, IraP and RpoS, and the matrix components as Sth fimbriae, Vi capsule and lipopolysaccharide. We discovered that the starvation sigma factor, RpoS, was required for the transcriptional activation of matrix-encoding genes in vitro, and for S. Typhi colonization in persistent infections in vivo, using a heterologous fish larval model. Overall, our work established a novel RpoS-driven paradigm for the formation of cholesterol-attached Typhi biofilms and emphasized the role(s) of stress signaling pathways for adaptation in chronic infections.

Dehydration induced AePer50 regulates midgut infection in Ae. aegypti.

In the face of climate change, mosquitoes will experience evolving climates including longer periods of drought. An important physiological response to dry environments is the protection against water loss or dehydration, here defined as desiccation tolerance. Various environmental factors including temperature are known to alter interactions between the mosquito, Aedes aegypti , and the arboviruses it transmits, but little is known about how low humidity impacts arboviral infection. Here, we report that a gene upregulated in response to desiccation is important for controlling midgut infection. We have identified two genetically diverse lines of Ae. aegypti with marked differences in desiccation tolerance. To understand if the genetic basis underlying desiccation tolerance is the same between the contrasting lines, we compared gene expression profiles between desiccant treated and non-desiccant treated individuals in both the desiccation tolerant and susceptible lines by RNAseq. Gene expression analysis demonstrates that different genes are differentially expressed in response to desiccation stress between desiccation tolerant and susceptible lines. The most highly expressed transcript under desiccation stress in the desiccation susceptible line encodes a peritrophin protein, Ae Per50. Peritrophins play a crucial role in peritrophic matrix formation after a bloodmeal. Gene silencing of Ae Per50 by RNAi demonstrates that expression of Ae Per50 is required for survival of the desiccation susceptible line under desiccation stress, but not for the desiccation tolerant line. Moreover, the knockdown of Ae Per50 results in higher infection rates and viral replication rates of ZIKV and higher infection rates of CHIKV. Finally, following a bloodmeal, the desiccation susceptible line develops a thicker peritrophic matrix than the desiccation tolerant line. Together these results provide a functional link between the protection against desiccation and midgut infection which has important implications in predicting how climate change will impact mosquito-borne viruses.

Necrotizing plasma cell-rich aortitis and sudden cardiac death: Late sequelae of COVID-19?

The ongoing epidemic caused by the coronavirus SARS-CoV-2 is characterized by a variety of pathologic processes within the syndrome of COVID-19. Usually beginning as an upper respiratory infection with potential progression to a pneumonitis, many cases of COVID-19 that show minimal signs or symptoms initially may develop adverse systemic sequelae later, such as widespread thrombo-embolic phenomena, systemic inflammatory disorders (especially in children), or vasculitis. Here, we present a patient who suffered a sudden cardiac death following persistent SARS-CoV-2 viral positivity for four-and-one-half months after a mild clinical viral course. At routine autopsy, a remarkable plasma cell-rich necrotizing aortitis was uncovered. The aortic intima displayed diffuse, circumferential ongoing chronic intimal edema, inflammation, and neo-vascularization. The plasma cell-rich inflammatory process also involved the origin of the left main coronary artery (LM) causing a coronary arteritis accompanied by subacute, stenosing intimal vascular smooth muscle cell (VSMC) proliferation resulting in acute myocardial necrosis as a cause of death. A similar vasculitis and plaque were noted during the routine autopsy at the ostium of the celiac artery; vasculitis was not found systemically or in smaller caliber vessels. Through a variety of techniques including extensive histopathologic and immunohistochemical characterization, immunostaining localization of viral antigen, and transmission electron microscopy we present highly suggestive evidence that this unique necrotizing, plasma cell-rich aortitis is a rare sequela of COVID-19.

Dysregulated pancreatic lipid phenotype, inflammation and cellular injury in a chronic ethanol feeding model of hepatic alcohol dehydrogenase-deficient deer mice.

AIMS: Dysregulation of pancreatic fat and lipotoxic inflammation are common clinical findings in alcoholic chronic pancreatitis (ACP). In this study, we investigated a relationship between dysregulated pancreatic lipid metabolism and the development of injury in a chronic ethanol (EtOH) feeding model of hepatic alcohol dehydrogenase 1- deficient (ADH-) deer mice. METHODS: ADH- and hepatic ADH normal (ADH+) deer mice were fed a liquid diet containing 3 % EtOH for three months and received a single gavage of binge EtOH with/without fatty acid ethyl esters (FAEEs) one week before the euthanasia. Plasma and pancreatic tissue were analyzed for lipids including FAEEs, inflammatory markers and adipokines using GC-MS, bioassays/kits, and immunostaining, respectively. Pancreatic morphology and proteins involved in lipogenesis were determined by the H & E staining, electron microscopy and Western blot analysis. KEY FINDINGS: Chronic EtOH feeding in ADH- vs. ADH+ deer mice resulted in a significant increase in the levels of pancreatic lipids including FAEEs, adipokines (leptin and resistin), fat infiltration with inflammatory cells and lipid droplet deposition along with the proteins involved in lipogenesis. The changes exacerbated by an administration of binge EtOH with/without FAEEs in the pancreas of ADH- vs. ADH+ deer mice fed chronic EtOH suggest a metabolic basis for ACP. SIGNIFICANCE: These findings suggest that the liver-pancreatic axis plays a crucial role in etiopathogenesis of ACP, as the increased body burden of EtOH due to hepatic ADH deficiency exacerbates pancreatic injury.

Characterization of an air-liquid interface primary human vaginal epithelium to study Ebola virus infection and testing of antivirals.

Ebola virus (EBOV) is the causative agent of the often-fatal Ebola virus disease (EVD) characterized by hemorrhagic fever in humans and non-human primates. Sexual transmission from male survivors has been at the origin of multiple outbreak flare-ups between 2015 and 2021. However, this route is still poorly understood and the resulting EVD from it is also understudied. To support epidemiological studies documenting sexual transmission to women, and as a transition from previously using monolayer vaginal epithelial cells (VK2/E6E7), we first determined the biological relevance of two similar air-liquid interface models of the human vaginal epithelium (VEC and VLC Epivaginal™) and then characterized their susceptibility to EBOV and virus-induced inflammation. Finally, we evaluated toxicity of Polyphenylene Carboxymethylene (PPCM) microbicide in VLC and reassessed its antiviral effect. As expected, the VEC, but also VLC model showed stratified layers including a lamina propria under an epithelial structure similar to the full thickness of the human vaginal epithelium. However, we could not detect the immune cells featured in the most relevant model (VLC) of the vaginal epithelium using the dendritic cell CD1a and CD11c markers. Consistent with our previous work using the VK2/E6E7 cell line, infectious virus was detected from the apical side of both primary human cell systems, but only when using a high infective dose, with titers remaining at a constant level of 103-4 pfu/ml over 7 days suggesting lasting infectious virus shedding. In addition, infection caused disruption of the epithelium of both models and virus antigen was found from the apical superficial layers down to the lamina propria suggesting full virus penetration and overall confirming the susceptibility of the human vaginal tissue for EBOV. Just like previously seen in VK2/E6E7 cells, VLC infection also caused significant increase in inflammatory markers including IL-6, IL-8, and IP-10 suggesting vaginitis which is again consistent with tissue lesions seen in non-human primates. Finally, both virus infection and virus-induced inflammatory response in VLC could be prevented by a single 5-min PPCM microbicide treatment prior infection.

Morphologic and Genetic Characterization of Ilheus Virus, a Potential Emergent Flavivirus in the Americas.

Ilheus virus (ILHV) is a mosquito-borne flavivirus circulating throughout Central and South America and the Caribbean. It has been detected in several mosquito genera including Aedes and Culex, and birds are thought to be its primary amplifying and reservoir host. Here, we describe the genomic and morphologic characterization of ten ILHV strains. Our analyses revealed a high conservation of both the 5'- and 3'-untranslated regions but considerable divergence within the open reading frame. We also showed that ILHV displays a typical flavivirus structural and genomic organization. Our work lays the foundation for subsequent ILHV studies to better understand its transmission cycles, pathogenicity, and emergence potential.

Characterization of an alloherpesvirus from wild lake sturgeon Acipenser fulvescens in Wisconsin (USA).

In the spring of 2017, 2 adult lake sturgeon (LS) Acipenser fulvescens captured from the Wolf River, Wisconsin (USA), presented with multiple cutaneous plaques that, upon microscopic examination, indicated proliferative epidermitis. Ultrastructural examination of affected keratinocytes revealed particles in the nucleus having a morphology typical of herpesviruses. A degenerate PCR assay targeting the DNA polymerase catalytic subunit (pol) gene of large double-stranded DNA viruses generated amplicons of the anticipated size from skin samples, and sequences of amplicons confirmed the presence of a novel alloherpesvirus (lake sturgeon herpesvirus, LSHV) related to acipenserid herpesvirus 1 (AciHV1). The complete genome (202660 bp) of this virus was sequenced using a MiSeq System, and phylogenetic analyses substantiated the close relationship to AciHV1. A PCR assay targeting the LSHV DNA packaging terminase subunit 1 (ter1) gene demonstrated the presence of the virus in 39/42 skin lesion samples collected from wild LS captured in 2017-2019 and 2021 in 4/4 rivers in Wisconsin. Future efforts to isolate LSHV in cell culture would facilitate challenge studies to determine the disease potential of the virus.

A novel group of negative-sense RNA viruses associated with epizootics in managed and free-ranging freshwater turtles in Florida, USA.

Few aquatic animal negative-sense RNA viruses have been characterized, and their role in disease is poorly understood. Here, we describe a virus isolated from diseased freshwater turtles from a Florida farm in 2007 and from an ongoing epizootic among free-ranging populations of Florida softshell turtles (Apalone ferox), Florida red-bellied cooters (Pseudemys nelsoni), and peninsula cooters (Pseudemys peninsularis). Affected turtles presented with similar neurological signs, oral and genital ulceration, and secondary microbial infections. Microscopic lesions were most severe in the softshell turtles and included heterophilic/histiocytic meningoencephalitis, multi-organ vasculitis, and cytologic observation of leukocytic intracytoplasmic inclusions. The virus was isolated using Terrapene heart (TH-1) cells. Ultrastructurally, viral particles were round to pleomorphic and acquired an envelope with prominent surface projections by budding from the cell membrane. Viral genomes were sequenced from cDNA libraries of two nearly identical isolates and determined to be bi-segmented, with an ambisense coding arrangement. The larger segment encodes a predicted RNA-directed RNA polymerase (RdRP) and a putative zinc-binding matrix protein. The smaller segment encodes a putative nucleoprotein and an envelope glycoprotein precursor (GPC). Thus, the genome organization of this turtle virus resembles that of arenaviruses. Phylogenetic analysis shows that the RdRP of the turtle virus is highly diverged from the RdRPs of all known negative-sense RNA viruses and forms a deep branch within the phylum Negarnaviricota, that is not affiliated with any known group of viruses, even at the class level. In contrast, the GPC protein of the turtle virus is confidently affiliated with homologs from a distinct group of fish hantaviruses. Thus, the turtle virus is expected to become the founder of a new taxon of negative-sense RNA viruses, at least with a family rank, but likely, an order or even a class. These viruses probably evolved either by reassortment or by intrasegment recombination between a virus from a distinct branch of negarnaviruses distant from all known groups and a hanta-like aquatic virus. We suggest the provisional name Tosoviridae for the putative new family, with Turtle fraservirus 1 (TFV1) as the type species within the genus Fraservirus. A conventional RT-PCR assay, targeting the TFV1 RdRP, confirmed the presence of viral RNA in multiple tissues and exudates from diseased turtles. The systemic nature of the TFV1 infection was further supported by labeling of cells within lesions using in situ hybridization targeting the RNA of the TFV1 RdRP.

Y-Box Binding Protein 1 Interacts with Dengue Virus Nucleocapsid and Mediates Viral Assembly.

Infection with dengue virus (DENV) induces vast rearrangements of the endoplasmic reticulum, which allows the compartmentalization of viral RNA replication and particle assembly. Both processes occur in concert with viral and cellular proteins. Prior studies from our group suggest that the host RNA-binding protein (RBP) Y-box binding protein 1 (YBX1) is required for a late step in the DENV replication cycle. Here we report that YBX1 interacts with the viral nucleocapsid, distributes to DENV assembly sites and is required for efficient assembly of intracellular infectious virions and their secretion. Genetic ablation of YBX1 decreased the spatial proximity between capsid and envelope, increased the susceptibility of envelope to proteinase K mediated degradation, resulted in the formation of rough empty-looking particles, and decreased the secretion of viral particles. We propose a model wherein YBX1 enables the interaction between the viral nucleocapsid with the structural protein E, which is required for proper assembly of intracellular virus particles and their secretion. IMPORTANCE The global incidence of dengue virus (DENV) infections has steadily increased over the past decades representing an enormous challenge for public health. During infection, DENV viral RNA interacts with numerous host RNA binding proteins (RBPs) that aid viral replication and thus constitute potential molecular targets to curb infection. We recently reported that Y-box-binding protein 1 (YBX1) interacts with DENV RNA and is required at a late step of the replication cycle. Here we describe the molecular mechanism by which YBX1 mediates DENV infection. We show that YBX1 interacts with the viral nucleocapsid, distributes to DENV assembly sites and is required for efficient assembly of intracellular infectious virions. These results provide important insights into DENV assembly, revealing novel functions of host RBPs during viral infection and opening new avenues for antiviral intervention.

Exposure to binge ethanol and fatty acid ethyl esters exacerbates chronic ethanol-induced pancreatic injury in hepatic alcohol dehydrogenase-deficient deer mice.

Alcoholic chronic pancreatitis (ACP) is a fibroinflammatory disease of the pancreas. However, metabolic basis of ACP is not clearly understood. In this study, we evaluated differential pancreatic injury in hepatic alcohol dehydrogenase-deficient (ADH-) deer mice fed chronic ethanol (EtOH), chronic plus binge EtOH, and chronic plus binge EtOH and fatty acid ethyl esters (FAEEs, nonoxidative metabolites of EtOH) to understand the metabolic basis of ACP. Hepatic ADH- and ADH normal (ADH+) deer mice were fed Lieber-DeCarli liquid diet containing 3% (wt/vol) EtOH for 3 mo. One week before the euthanization, chronic EtOH-fed mice were further administered with an oral gavage of binge EtOH with/without FAEEs. Blood alcohol concentration (BAC), pancreatic injury, and inflammatory markers were measured. Pancreatic morphology, ultrastructural changes, and endoplasmic reticulum (ER)/oxidative stress were examined using H&E staining, electron microscopy, immunostaining, and/or Western blot, respectively. Overall, BAC was substantially increased in chronic EtOH-fed groups of ADH- versus ADH+ deer mice. A significant change in pancreatic acinar cell morphology, with mild to moderate fibrosis and ultrastructural changes evident by dilatations and disruption of ER cisternae, ER/oxidative stress along with increased levels of inflammatory markers were observed in the pancreas of chronic EtOH-fed groups of ADH- versus ADH+ deer mice. Furthermore, chronic plus binge EtOH and FAEEs exposure elevated BAC, enhanced ER/oxidative stress, and exacerbated chronic EtOH-induced pancreatic injury in ADH- deer mice suggesting a role of increased body burden of EtOH and its metabolism under reduced hepatic ADH in initiation and progression of ACP.NEW & NOTEWORTHY We established a chronic EtOH feeding model of hepatic alcohol dehydrogenase-deficient (ADH-) deer mice, which mimics several fibroinflammatory features of human alcoholic chronic pancreatitis (ACP). The fibroinflammatory and morphological features exacerbated by chronic plus binge EtOH and FAEEs exposure provide a strong case for metabolic basis of ACP. Most importantly, several pathological and molecular targets identified in this study provide a much broader understanding of the mechanism and avenues to develop therapeutics for ACP.

RBFOX2 is critical for maintaining alternative polyadenylation patterns and mitochondrial health in rat myoblasts.

RBFOX2, which has a well-established role in alternative splicing, is linked to heart diseases. However, it is unclear whether RBFOX2 has other roles in RNA processing that can influence gene expression in muscle cells, contributing to heart disease. Here, we employ both 3'-end and nanopore cDNA sequencing to reveal a previously unrecognized role for RBFOX2 in maintaining alternative polyadenylation (APA) signatures in myoblasts. RBFOX2-mediated APA modulates mRNA levels and/or isoform expression of a collection of genes, including contractile and mitochondrial genes. Depletion of RBFOX2 adversely affects mitochondrial health in myoblasts, correlating with disrupted APA of mitochondrial gene Slc25a4. Mechanistically, RBFOX2 regulation of Slc25a4 APA is mediated through consensus RBFOX2 binding motifs near the distal polyadenylation site, enforcing the use of the proximal polyadenylation site. In sum, our results unveil a role for RBFOX2 in fine-tuning expression of mitochondrial and contractile genes via APA in myoblasts relevant to heart diseases.

Novel cetacean morbillivirus in a rare Fraser's dolphin (Lagenodelphis hosei) stranding from Maui, Hawai'i.

Cetacean morbillivirus (CeMV) is a global threat to cetaceans. We report a novel morbillivirus from a Fraser's dolphin (Lagenodelphis hosei) that stranded in Maui, Hawaii in 2018 that is dissimilar to the beaked whale morbillivirus previously identified from Hawaii and to other CeMV strains. Histopathological findings included intranuclear inclusions in bile duct epithelium, lymphoid depletion, rare syncytial cells and non-suppurative meningitis. Cerebellum and lung tissue homogenates were inoculated onto Vero.DogSLAMtag cells for virus isolation and cytopathic effects were observed, resulting in the formation of multinucleated giant cells (i.e., syncytia). Transmission electron microscopy of infected cell cultures also revealed syncytial cells with intracytoplasmic and intranuclear inclusions of viral nucleocapsids, consistent with the ultrastructure of a morbillivirus. Samples of the cerebellum, lung, liver, spleen and lymph nodes were positive for morbillivirus using a reverse transcription-polymerase chain reaction. The resulting 559 bp L gene sequence had the highest nucleotide identity (77.3%) to porpoise morbillivirus from Northern Ireland and the Netherlands. The resulting 248 bp P gene had the highest nucleotide identity to porpoise morbillivirus in Northern Ireland and the Netherlands and to a stranded Guiana dolphin (Sotalia guianensis) in Brazil (66.9%). As Fraser's dolphins are a pelagic species that infrequently strand, a novel strain of CeMV may be circulating in the central Pacific that could have additional population impacts through transmission to other small island-associated cetacean species.

Complete genome sequences of infectious spleen and kidney necrosis virus isolated from farmed albino rainbow sharks Epalzeorhynchos frenatum in the United States.

The genus Megalocytivirus includes viruses known to cause significant disease in aquacultured fish stocks. Herein, we report the complete genome sequences of two megalocytiviruses (MCVs) isolated from diseased albino rainbow sharks Epalzeorhynchos frenatum reared on farms in the United States in 2018 and 2019. Histopathological examination revealed typical megalocytivirus microscopic lesions (i.e., basophilic cytoplasmic inclusions) that were most commonly observed in the spleen and kidney. Transmission electron microscopic examination of spleen and kidney tissues from specimens of the 2018 case revealed hexagonally shaped virus particles with a mean diameter of 153 ± 6 nm (n = 20) from opposite vertices and 131 ± 5 nm (n = 20) from opposite faces. Two MCV-specific conventional PCR assays confirmed the presence of MCV DNA in the collected samples. Full genome sequencing of both 2018 and 2019 Epalzeorhynchos frenatus iridoviruses (EFIV) was accomplished using a next-generation sequencing approach. Phylogenomic analyses revealed that both EFIV isolates belong to the infectious spleen and kidney necrosis virus (ISKNV) genotype within the genus Megalocytivirus. This study is the first report of ISKNV in albino rainbow sharks.

Isolation of a novel insect-specific flavivirus with immunomodulatory effects in vertebrate systems.

We describe the isolation and characterization of a novel insect-specific flavivirus (ISFV), tentatively named Aripo virus (ARPV), that was isolated from Psorophora albipes mosquitoes collected in Trinidad. The ARPV genome was determined and phylogenetic analyses showed that it is a dual host associated ISFV, and clusters with the main mosquito-borne flaviviruses. ARPV antigen was significantly cross-reactive with Japanese encephalitis virus serogroup antisera, with significant cross-reactivity to Ilheus and West Nile virus (WNV). Results suggest that ARPV replication is limited to mosquitoes, as it did not replicate in the sandfly, culicoides or vertebrate cell lines tested. We also demonstrated that ARPV is endocytosed into vertebrate cells and is highly immunomodulatory, producing a robust innate immune response despite its inability to replicate in vertebrate systems. We show that prior infection or coinfection with ARPV limits WNV-induced disease in mouse models, likely the result of a robust ARPV-induced type I interferon response.

High molecular weight sodium hyaluronate improves survival of syndecan-1-deficient septic mice by inhibiting neutrophil migration.

METHODS: Sepsis was induced by cotton smoke inhalation followed by intranasal administration of Pseudomonas aeruginosa in female (> 6 months) Balb/c and syndecan-1 knockout mice. Survival of mice, lung capillary endothelial glycocalyx integrity, lung water content, and vascular hyper-permeability were determined with or without HMW-SH treatment in these mice. Effects of HMW-SH on endothelial permeability and neutrophil migration were tested in in vitro setting. RESULTS: In septic wildtype mice, we found a severely damaged pulmonary microvascular endothelial glycocalyx and elevated levels of shed syndecan-1 in the circulation. These changes were associated with significantly increased pulmonary vascular permeability. In septic syndecan-1 knockout mice, extravascular lung water content was higher, and early death was observed. The administration of HMW-SH significantly reduced mortality and lung water content in septic syndecan-1 knockout mice, but not in septic wildtype mice. In in vitro setting, HMW-SH inhibited neutrophil migration and reduced cultured endothelial cell permeability increases. However, these effects were reversed by the addition of recombinant syndecan-1 ectodomain. CONCLUSIONS: HMW-SH reduced lung tissue damage and mortality in the absence of syndecan-1 protein, possibly by reducing vascular hyper-permeability and neutrophil migration. Our results further suggest that increased shed syndecan-1 protein levels are linked with the inefficiency of HMW-SH in septic wildtype mice.

Endoderm and Hepatic Progenitor Cells Engraft in the Quiescent Liver Concurrent with Intrinsically Activated Epithelial-to-Mesenchymal Transition.

Stem cell transplantation to the liver is a promising therapeutic strategy for a variety of disorders. Hepatocyte transplantation has short-term efficacy but can be problematic due to portal hypertension, inflammation, and sinusoidal thrombosis. We have previously transplanted small mouse endoderm progenitor (EP) cells to successfully reverse a murine model of hemophilia B, and labeling these cells with iron nanoparticles renders them responsive to magnetic fields, which can be used to enhance engraftment. The mechanisms mediating progenitor cell migration from the sinusoidal space to the hepatocyte compartment are unknown. Here we find human EP and hepatic progenitor (HP) cells can be produced from human embryonic stem cells with high efficiency, and they also readily uptake iron nanoparticles. This provides a simple manner through which one can readily identify transplanted cells in vivo using electron microscopy, shortly after delivery. High resolution imaging shows progenitor cell morphologies consistent with epithelial-to-mesenchymal transition (EMT) mediating invasion into the hepatic parenchyma. This occurs in as little as 3 h, which is considerably faster than observed when hepatocytes are transplanted. We confirmed activated EMT in transplanted cells in vitro, as well as in vivo 24 h after transplantation. We conclude that EMT naturally occurs concurrent with EP and HP cell engraftment, which may mediate the rate, safety, and efficacy of early cell engraftment in the undamaged quiescent liver.

Loss of furin cleavage site attenuates SARS-CoV-2 pathogenesis.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-a new coronavirus that has led to a worldwide pandemic1-has a furin cleavage site (PRRAR) in its spike protein that is absent in other group-2B coronaviruses2. To explore whether the furin cleavage site contributes to infection and pathogenesis in this virus, we generated a mutant SARS-CoV-2 that lacks the furin cleavage site (ΔPRRA). Here we report that replicates of ΔPRRA SARS-CoV-2 had faster kinetics, improved fitness in Vero E6 cells and reduced spike protein processing, as compared to parental SARS-CoV-2. However, the ΔPRRA mutant had reduced replication in a human respiratory cell line and was attenuated in both hamster and K18-hACE2 transgenic mouse models of SARS-CoV-2 pathogenesis. Despite reduced disease, the ΔPRRA mutant conferred protection against rechallenge with the parental SARS-CoV-2. Importantly, the neutralization values of sera from patients with coronavirus disease 2019 (COVID-19) and monoclonal antibodies against the receptor-binding domain of SARS-CoV-2 were lower against the ΔPRRA mutant than against parental SARS-CoV-2, probably owing to an increased ratio of particles to plaque-forming units in infections with the former. Together, our results demonstrate a critical role for the furin cleavage site in infection with SARS-CoV-2 and highlight the importance of this site for evaluating the neutralization activities of antibodies.

Microbial interactions in the mosquito gut determine Serratia colonization and blood-feeding propensity.

How microbe-microbe interactions dictate microbial complexity in the mosquito gut is unclear. Previously we found that, Serratia, a gut symbiont that alters vector competence and is being considered for vector control, poorly colonized Aedes aegypti yet was abundant in Culex quinquefasciatus reared under identical conditions. To investigate the incompatibility between Serratia and Ae. aegypti, we characterized two distinct strains of Serratia marcescens from Cx. quinquefasciatus and examined their ability to infect Ae. aegypti. Both Serratia strains poorly infected Ae. aegypti, but when microbiome homeostasis was disrupted, the prevalence and titers of Serratia were similar to the infection in its native host. Examination of multiple genetically diverse Ae. aegypti lines found microbial interference to S. marcescens was commonplace, however, one line of Ae. aegypti was susceptible to infection. Microbiome analysis of resistant and susceptible lines indicated an inverse correlation between Enterobacteriaceae bacteria and Serratia, and experimental co-infections in a gnotobiotic system recapitulated the interference phenotype. Furthermore, we observed an effect on host behavior; Serratia exposure to Ae. aegypti disrupted their feeding behavior, and this phenotype was also reliant on interactions with their native microbiota. Our work highlights the complexity of host-microbe interactions and provides evidence that microbial interactions influence mosquito behavior.